Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Mar. 01, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	AKBA
Entity Registrant Name	Akebia Therapeutics, Inc.
Entity Central Index Key	0001517022
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		48,346,171
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 576,393,274

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 70,156	$ 187,335
Available for sale securities	247,636	73,008
Accounts receivable	34,216	33,823
Prepaid expenses and other current assets	6,348	2,155
Total current assets	358,356	296,321
Property and equipment, net	3,617	2,612
Other assets	2,274	1,283
Total assets	364,247	300,216
Current liabilities:
Accounts payable	6,998	2,039
Accrued expenses	52,441	30,261
Short-term deferred revenue	84,910	81,968
Total current liabilities	144,349	114,268
Deferred rent, net of current portion	2,588	2,480
Deferred revenue, net of current portion	97,957	115,321
Other non-current liabilities	22	27
Total liabilities	244,916	232,096
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized at December 31, 2017 and 2016; 0 shares issued and outstanding at December 31, 2017 and 2016
Common stock: $0.00001 par value; 175,000,000 shares authorized at December 31, 2017 and 2016; 47,612,619 and 38,615,709 shares issued and outstanding at December 31, 2017 and 2016, respectively	0	0
Additional paid-in capital	493,823	365,298
Accumulated other comprehensive income (loss)	(442)	(42)
Accumulated deficit	(374,050)	(297,136)
Total stockholders' equity	119,331	68,120
Total liabilities and stockholders' equity	$ 364,247	$ 300,216

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	47,612,619	38,615,709
Common stock, shares outstanding	47,612,619	38,615,709

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Collaboration revenue	$ 177,984	$ 1,535
Operating expenses:
Research and development	230,893	115,785	$ 43,016
General and administrative	27,008	22,210	18,497
Total operating expenses	257,901	137,995	61,513
Operating loss	(79,917)	(136,460)	(61,513)
Other income (expense):
Interest income	2,799	901	510
Other income/(expense)	204	(188)	287
Net loss	$ (76,914)	$ (135,747)	$ (60,716)
Net loss per share - basic and diluted	$ (1.77)	$ (3.60)	$ (2.29)
Weighted-average number of common shares - basic and diluted	43,500,795	37,716,949	26,469,170
Comprehensive loss:
Net loss	$ (76,914)	$ (135,747)	$ (60,716)
Other comprehensive loss - unrealized loss on securities	(400)	(42)	(234)
Total comprehensive loss	$ (77,314)	$ (135,789)	$ (60,950)

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Unrealized Gain/Loss	Accumulated Deficit
Balance at Dec. 31, 2014	$ 104,078		$ 204,969	$ (162)	$ (56)	$ (100,673)
Balance, shares at Dec. 31, 2014		20,370,624
Issuance of common stock, net of issuance costs	82,750		82,750
Issuance of common stock, net of issuance costs, shares		10,083,070
Proceeds from sale of stock under employee stock purchase plan	220		220
Proceeds from sale of stock under employee stock purchase plan, shares		25,903
Forfeitures of restricted common stock, shares		(36,053)
Exercise of options	130		130
Exercise of options, shares		218,674
Share-based compensation expense	4,714		4,714
Unrealized gain/loss	(178)				(178)
Net loss	(60,716)					(60,716)
Balance at Dec. 31, 2015	130,998		292,783	(162)	(234)	(161,389)
Balance, shares at Dec. 31, 2015		30,662,218
Issuance of common stock, net of issuance costs	66,623		66,623
Issuance of common stock, net of issuance costs, shares		7,865,293
Proceeds from sale of stock under employee stock purchase plan	105		105
Proceeds from sale of stock under employee stock purchase plan, shares		16,629
Forfeitures of restricted common stock, shares		(15,056)
Exercise of options	124		124
Exercise of options, shares		86,625
Share-based compensation expense	5,825		5,825
Unrealized gain/loss	192				192
Treasury shares retired (8,643)			(162)	$ 162
Net loss	(135,747)					(135,747)
Balance at Dec. 31, 2016	$ 68,120		365,298		(42)	(297,136)
Balance, shares at Dec. 31, 2016	38,615,709	38,615,709
Issuance of common stock, net of issuance costs	$ 114,580		114,580
Issuance of common stock, net of issuance costs, shares		8,672,270
Proceeds from sale of stock under employee stock purchase plan	353		353
Proceeds from sale of stock under employee stock purchase plan, shares		44,833
Forfeitures of restricted common stock, shares		(2,406)
Exercise of options	$ 1,312		1,312
Exercise of options, shares	291,439	256,213
Share-based compensation expense	$ 8,867		8,867
Restricted stock unit vesting, shares		26,000
Issuance of common stock warrants	3,413		3,413
Unrealized gain/loss	(400)				(400)
Net loss	(76,914)					(76,914)
Balance at Dec. 31, 2017	$ 119,331		$ 493,823		$ (442)	$ (374,050)
Balance, shares at Dec. 31, 2017	47,612,619	47,612,619

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (76,914)	$ (135,747)	$ (60,716)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	617	296	96
Amortization of premium/discount on investments	610	494	558
Loss on disposal of property and equipment		306
Stock-based compensation	8,867	5,825	4,714
Fair value of warrants issued for license	3,413
Changes in operating assets and liabilities:
Accounts receivable	(393)	(33,823)
Prepaid expenses and other current assets	(4,193)	428	(1,001)
Other long-term assets	(991)	(2)	(976)
Accounts payable	4,959	(274)	231
Accrued expense	21,974	20,703	4,646
Deferred revenue	(14,422)	197,289
Deferred rent	314	2,411	41
Net cash provided by (used in) operating activities	(56,159)	57,906	(52,407)
Investing activities:
Purchase of equipment	(1,622)	(2,662)	(414)
Proceeds from the maturities of available for sale securities	149,998	162,376	63,901
Proceeds from sales of available for sale securities	5,000
Purchase of available for sale securities	(330,636)	(147,009)	(77,175)
Net cash provided by (used in) investing activities	(177,260)	12,705	(13,688)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	114,580	66,736	82,750
Proceeds from the sale of stock under employee stock purchase plan	353	106	220
Proceeds from the exercise of stock options	1,312	124	130
Payments on capital lease obligations	(5)	(20)	(7)
Net cash provided by financing activities	116,240	66,946	83,093
Increase in cash and cash equivalents	(117,179)	137,557	16,998
Cash and cash equivalents at beginning of the period	187,335	49,778	32,780
Cash and cash equivalents at end of the period	$ 70,156	187,335	49,778
Non-cash financing activities
Unpaid follow-on offering costs		$ 12	102
Assets acquired under capital lease			$ 12

Nature of Organization and Operations	12 Months Ended
Nature of Organization and Operations	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Akebia Therapeutics, Inc., referred to as Akebia or the Company, was incorporated in the State of Delaware in 2007. Akebia is a biopharmaceutical company focused on developing and commercializing novel therapeutics for patients based on hypoxia-inducible factor, or HIF, biology, and building its pipeline while leveraging its development and commercial expertise in renal disease. HIF is the primary regulator of the production of red blood cells, or RBCs, in the body, as well as other important metabolic functions. Pharmacologic modulation of the HIF pathway may have broad therapeutic applications. The Company’s lead product candidate, vadadustat, is an oral therapy in Phase 3 development, and has the potential to set a new standard of care in the treatment of anemia due to chronic kidney disease, or CKD. The Company’s management team has extensive experience in developing and commercializing drugs for the treatment of renal and metabolic disorders, as well as a deep understanding of HIF biology. This unique combination of HIF and renal expertise is enabling the Company to advance a pipeline of HIF-based therapies to potentially address serious diseases. Since inception, the Company has devoted most of its resources to research and development, including its preclinical and clinical development activities, raising capital, and providing general and administrative support for these operations. The Company has not generated any product revenue to date and may never generate any product revenue in the future. The Company’s product candidates are subject to long development cycles, and the Company may be unsuccessful in its efforts to develop, obtain marketing approval for or market its product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding, including the resources necessary to fund the global Phase 3 program for vadadustat in non-dialysis dependent, or NDD-CKD, called PRO₂TECT, and dialysis dependent, or DD-CKD, called INNO₂VATE, risks of clinical trial failures, the risk of relying on third parties, the risk that the Company never achieves profitability, protection of proprietary technology, compliance with governmental regulations, and dependence on key personnel. In December 2015 the first subject was dosed in PRO₂TECT, and the first subject was dosed in INNO₂VATE in August 2016. Overall, the PRO₂TECT and INNO₂VATE Phase 3 programs are designed to enroll up to approximately 6,900 patients. The enrollment numbers and the completion of PRO₂TECT and INNO₂VATE will be subject to the accrual of major adverse cardiovascular events, or MACE. The Company anticipates reporting top-line clinical data for the PRO₂TECT and INNO₂VATE studies in 2019, subject to the accrual of MACE events. Subject to marketing approvals, we plan to launch vadadustat for the treatment of anemia due to CKD in 2020. Through 2017 the Company raised approximately $373.1 million of net proceeds, including $292.6 million from several underwritten public offerings, $30.5 million from an at-the-market offering, or ATM, pursuant to sales agreements with Cantor Fitzgerald & Co. and $50.0 million from the sale of 3,571,429 shares of common stock to Vifor (International) Ltd., or Vifor Pharma. At inception of our collaboration agreements with Otsuka Pharmaceutical Co. Ltd., or Otsuka and Mitsubishi Tanabe Pharma Corporation, or MTPC, they committed to approximately $573.0 million or more in cost-share funding, of which we generally continue to receive on a quarterly prepaid basis, and license payments. Of these commitments, we received approximately $272.0 million at the onset of the collaboration agreements. In December 2015, the Company entered into a collaboration agreement with MTPC to develop and commercialize vadadustat in Japan and certain other countries in Asia, collectively, the MTPC Territory, for total payments of up to $245.0 million, comprised of a $20.0 million upfront payment, up to $50.0 million in specified development and regulatory milestones, and up to $175.0 million in specified commercial milestones, as well as tiered double-digit royalty payments up to 20% on sales of vadadustat in the MTPC Territory (Note 3). In December 2016, the Company entered into a collaboration and license agreement with Otsuka to develop and commercialize vadadustat in the United States. In December 2016, the Company received $125.0 million upfront payment, and in March 2017, Otsuka reimbursed the Company approximately $33.8 million for global expenses previously incurred by us for our ongoing global development program for vadadustat in DD-CKD and NDD-CKD patients. The agreement also provides for additional funding for the global development program for vadadustat, totaling $153.6 million or more, depending on the actual global development costs incurred. In addition, Akebia is eligible to receive from Otsuka up to $190.0 million in specified development and regulatory milestones and up to $575.0 million in specified commercial milestones. We will share equally with Otsuka the costs of developing and commercializing vadadustat in the United States and the profits from sales of vadadustat after approval by the FDA (Note 3). In April 2017, the Company entered into a collaboration and license agreement with Otsuka to develop and commercialize vadadustat in Europe, Russia, China, Canada, Australia, the Middle East and certain other territories. In April 2017, the Company received a $73.0 million upfront payment and $0.2 million for global expenses previously incurred by the Company in implementing the current global development plan for vadadustat in DD-CKD and NDD-CKD patients in excess of a specified threshold during the quarter-ended March 31, 2017. The agreement also provides for additional funding for the global development program for vadadustat, totaling $163.6 million or more, depending on the actual global development costs incurred. In addition, Akebia is eligible to receive from Otsuka up to $132.0 million in specified development and regulatory milestones and up to $525.0 million in specified commercial milestones (Note 3). The Company believes that its existing cash and cash equivalents and available for sale securities of approximately $317.8 million at December 31, 2017, together with the committed funding from its collaboration partners, will be sufficient to allow the Company to fund its current operating plan into the second quarter of 2019, and as a result, through at least twelve months from the filing of the Company’s 2017 Annual Report on Form 10-K. There can be no assurance, however, that the current operating plan will be achieved in the time frame anticipated by the Company, or that its cash resources will fund the Company’s operating plan for the period anticipated by the Company or that additional funding will be available on terms acceptable to the Company, or at all. The Company will require additional capital for the further development of our existing product candidates and will need to raise additional funds to pursue development activities related to additional product candidates. If and until the Company can generate a sufficient amount of revenue from our products, we expect to finance future cash needs through public or private equity or debt offerings, payments from our collaborators, strategic transactions, or a combination of these approaches.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Akebia Therapeutics Securities Corporation and Akebia Europe Limited. All intercompany balances and transactions have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (U.S. GAAP). Any reference in these notes to applicable guidance is meant to refer to the authoritative U.S. GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Update (ASU) of the Financial Accounting Standards Board (FASB).

In the quarter ended June 30, 2017, the Company identified and corrected an immaterial error in the amount of research and development expenses related to the Company’s global Phase 3 program of vadadustat. This adjustment also affected the amount of revenue recognized pursuant to the Company’s license and collaboration agreements with Otsuka. The adjustments impacted our results of operations in each quarter of 2016 and the first quarter of 2017. The Company concluded the effect of these adjustments was not material to its consolidated financial statements for any prior period.

New Accounting Pronouncements – Recently Adopted

The Company adopted ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, effective in the first quarter of the year ended December 31, 2017. This ASU simplifies the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. The following summarizes the effects of the adoption on the Company's audited consolidated financial statements:

•

Income taxes - Upon adoption of this standard, all excess tax benefits and tax deficiencies, including tax benefits of dividends on share-based payment awards, are recognized as income tax expense or benefit in the income statement. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. The Company also recognizes excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. The Company has applied the modified retrospective adoption approach beginning in fiscal year 2017 and prior periods have not been adjusted. As a result, the Company will establish a net operating loss deferred tax asset of $0.4 million to account for prior period excess tax benefits through retained earnings, however an offsetting valuation allowance of $0.4 million will also be established through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses, such that there is no impact on the Company’s consolidated financial statements.

•

Forfeitures - Prior to adoption, share-based compensation expense was recognized on a straight-line basis, net of estimated forfeitures, such that expense was recognized only for share-based awards that are expected to vest. A forfeiture rate was estimated annually and revised, if necessary, in subsequent periods if actual forfeitures differed from initial estimates. Upon adoption of this standard, the Company will no longer apply a forfeiture rate and instead will account for forfeitures as they occur. As the Company previously estimated forfeitures to determine stock-based compensation expense, this change in accounting principle resulted in a cumulative-effect adjustment as of January 1, 2017 to reduce retained earnings by $0.2 million.

•

Earnings Per Share - The Company uses the treasury stock method to compute diluted earnings per share, unless the effect would be anti-dilutive. Under this method, the Company will no longer be required to estimate the tax rate and apply it to the dilutive share calculation for determining the dilutive earnings per share. The Company has applied this methodology beginning in fiscal year 2017, and prior periods have not been adjusted.

Upon adoption in January 2017, no other aspects of ASU 2016-09 had a material effect on the Company's unaudited condensed consolidated financial statements or related footnote disclosures.

In January 2017, the FASB issued an ASU 2017-01, Business Combinations (Topic 805) Clarifying the Definition of a Business. ASU 2017-01 clarifies the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The definition of a business affects many areas of accounting including acquisitions, disposals, goodwill, and consolidation. The guidance is effective for annual periods beginning after December 15, 2017, including interim periods within those periods. ASU 2017-01 may be adopted early. The Company adopted the provisions of ASC 2017-01 effective January 1, 2017. Adoption did not have a material impact on the Company's financial position, results of operations, or cash flows.

New Accounting Pronouncements – Not Yet Adopted

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), a new revenue recognition standard which amends revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The new standard provides a five-step framework whereby revenue is recognized when promised goods or services are transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires enhanced disclosures pertaining to revenue recognition in both interim and annual periods. In August 2015, the FASB deferred the effective date of the new revenue standard from January 1, 2017 to January 1, 2018. Early adoption is permitted any time after the original effective date, which for us was January 1, 2017. The Company intends to adopt the new standard on January 1, 2018. The standard allows for adoption using a full retrospective method for all periods presented in the period of adoption (with some limited relief provided) or a modified retrospective method.

The Company’s historical revenue has been derived from its collaboration agreements with Otsuka Pharmaceutical Co. Ltd., or Otsuka. The Company commenced revenue recognition under its collaboration agreement with Mitsubishi Tanabe Pharma Corporation, or MTPC, upon initiation of delivery of the clinical supply of vadadustat to MTPC for the Phase 3 studies of vadadustat sponsored by MTPC in Japan, which occurred in the fourth quarter of 2017. These arrangements contain multiple-elements and have been accounted for pursuant to ASC Topic 605‑25, Revenue Recognition Multiple‑Element Arrangements, or ASC 605‑25.

The new revenue standard creates ASC Topic 606, Revenue from Contracts with Customers, or ASC 606. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize when (or as) the entity satisfies a performance obligation. ASC 606 also impacts certain other areas, such as the accounting for costs to obtain or fulfill a contract. The standard also requires disclosure of the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers.

The Company will adopt the new standard effective January 1, 2018, using the full retrospective transition method. Under this method, the Company will revise its results for the years ended December 31, 2016 and 2017, as well as the applicable interim periods within those years as if ASC 606 had been effective for those periods. The Company has assessed the effect of adoption of this standard as it relates to its collaboration agreements with Otsuka and MTPC. Currently, the Company anticipates the effects of adoption to be as described below. Estimated impacts from the adoption of this standard could differ upon the final adoption and implementation of the standard.

The Company expects the accounting for contingent milestone payments to be the most significant change in the accounting for its collaboration agreements. Under ASC 605-28, Revenue Recognition-Milestone Method, the Company evaluates at inception of an arrangement whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. Milestones that are considered substantive are recognized as revenue in their entirety upon achievement, assuming all other revenue criteria are met. Milestones that are not considered substantive are recognized as revenue upon achievement if there are no remaining performance obligations or over the remaining period of performance if there are remaining performance obligations, assuming all other revenue recognition criteria are met. However, under ASC 606, there is no specific guidance as it relates to milestone payments. Therefore, under the new standard, milestone payments are to be considered in accordance with the overall model of ASC 606, which requires an assessment at each reporting date of the probability of achievement of the milestone and the likelihood that a significant reversal in the cumulative amount of revenue recognized will not occur. This assessment may result in contingent milestone payments being recognized before the milestone event has occurred and therefore would result in revenue being recognized earlier than under ASC 605. In addition, ASC 606 changes guidance regarding the accounting for variable consideration received from licensees, which may impact the estimation of, and determination of the timing of, the related revenue recognition.

With respect to the collaboration agreements with Otsuka, the Company currently estimates no impact to revenue for the years ended December 31, 2017 and 2016 after the adoption of ASC 606. With respect to the MTPC collaboration agreement, the Company estimates an increase in revenue of $3.2 million and $0 for the years ended December 31, 2017 and 2016, respectively, after the adoption of ASC 606. The change in revenue is due to the timing of when milestone payments can be recognized under the new standard as well as the period over which this revenue is recognized. As noted in the previous paragraph, under ASC 605-28, certain milestones that are considered substantive at inception of an arrangement are recognized as revenue in their entirety upon achievement. However, under ASC 606, these substantive milestone payments would be classified as variable consideration and included in the allocable transaction price over the remaining period of performance when it is probable that a significant reversal in the cumulative amount of revenue recognized would not occur.

In addition to the effects on collaboration revenue, the Company expects to revise balances of working capital components associated with collaboration revenues, such as accounts receivable and deferred revenue. Overall, the Company currently expects current assets to increase as a result of these changes by $3.2 million and $0 as of December 31, 2017 and 2016, respectively, and it currently expects no changes in current liabilities for both December 31, 2017 and 2016.

The quantitative changes provided above are estimates of the expected effects of the Company’s adoption of ASC 606. These changes represent management’s best estimates of the effects of adopting ASC 606 at the time of the preparation of this Annual Report on Form 10-K. The actual, final quantitative effects of the adoption of ASC 606 are subject to change from these estimates and such change may be significant, pending the completion of the Company’s assessment in the first quarter of 2018.

Finally, ASC 606 requires more robust disclosures than required by previous guidance, including disclosures related to disaggregation of revenue into appropriate categories, performance obligations, the judgments made in revenue recognition determinations, adjustments to revenue which relate to activities from previous quarters or years, any significant reversals of revenue, and costs to obtain or fulfill contracts.

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which supersedes the existing guidance for lease accounting, Leases (Topic 840). ASU 2016-02 requires entities to recognize right-of-use assets and lease liabilities on their balance sheets and provide enhanced disclosures. The amendments in ASU 2016-02 are effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early application is permitted for all entities, however, at this time, the Company does not intend to early adopt. ASU 2016-02 requires a modified retrospective approach for all leases existing at, or entered into after, the date of initial application, with an option to elect to use certain transition relief. The Company is currently evaluating the impact of this new standard on its consolidated financial statements and related disclosures.

In October 2016, the FASB issued ASU 2016-18, Restricted Cash, which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally describes as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, and interim periods within those years, using a retrospective transition method to each period presented. Early adoption is permitted. The Company is evaluating the potential impact that the adoption of ASU 2016-18 will have on the Company’s financial position or results of operations.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing novel therapeutics for patients based on HIF biology and building its pipeline while leveraging its development and commercial expertise in renal disease.

Derivative Financial Instruments

The Company accounts for warrants and other derivative financial instruments as either equity or liabilities in accordance with ASC Topic 815, Derivatives and Hedging, or ASC 815, based upon the characteristics and provisions of each instrument. Warrants classified as equity are recorded at fair value as of the date of issuance on the Company’s consolidated balance sheets and no further adjustments to their valuation are made. Warrants classified as derivative liabilities and other derivative financial instruments that require separate accounting as liabilities are recorded on the Company’s consolidated balance sheets at their fair value on the date of issuance and will be revalued on each subsequent balance sheet date until such instruments are exercised or expire, with any changes in the fair value between reporting periods recorded as other income or expense. The warrant issued by the Company in connection with the Janssen Pharmaceutica NV Research and License Agreement, the Janssen Agreement, is classified as equity in the Company’s consolidated balance sheet. (See Note 7).

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: prepaid and accrued research and development expense, stock-based compensation expense, revenue and income taxes.

Cash and Cash Equivalents

Cash and cash equivalents consist of all cash on hand, deposits and funds invested in available for sale securities with original maturities of three months or less at the time of purchase. Cash equivalents are reported at fair value. At December 31, 2017, the Company’s cash equivalents are primarily in money market funds. The Company may maintain balances with its banks in excess of federally insured limits.

Investments

Management determines the appropriate classification of securities at the time of purchase and reevaluates such designation as of each balance sheet date. Currently, the Company classifies all securities as available for sale which are included in current assets as they are intended to fund current operations. The Company carries available for sale securities at fair value. The Company conducts periodic reviews to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment and its application to certain investments. When assessing whether a decline in the fair value of a security is other-than-temporary, the Company considers the fair market value of the security, the duration of the security’s decline, and prospects for the underlying business. Based on these considerations, the Company did not identify any other-than-temporary unrealized losses at December 31, 2017. Unrealized losses on available for sale securities that are determined to be temporary, and not related to credit loss, are recorded in accumulated other comprehensive loss, a component of stockholders’ equity. The amortized cost of debt securities in this category reflects amortization of premiums and accretion of discounts to maturity computed under the effective interest method. The Company includes this amortization in the caption “Interest income” within the consolidated statements of operations and comprehensive loss. The Company also includes in net investment income, realized gains and losses and declines in value determined to be other than temporary. The Company bases the cost of securities sold upon the specific identification method and includes interest and dividends on securities in interest income.

Accounts Receivable

The Company’s accounts receivable represents amounts due to the Company from its collaboration agreements with MTPC and Otsuka (see Note 3). Reimbursable costs that have not been invoiced as of the balance sheet date are recorded as unbilled accounts receivable. The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company believes that credit risks associated with its collaboration partners are not significant. To date, the Company has not had any write-offs of bad debt, and the Company did not have an allowance for doubtful accounts as of December 31, 2017 and 2016.

Revenue Recognition

To date, the Company has not generated any revenue from the sales of products. For the foreseeable future, the Company expects substantially all of its revenues will be generated from its collaborations with MTPC and Otsuka (see Note 3) and any other collaborations the Company may enter into.

Multiple-Element Arrangements

The Company recognizes revenue in accordance with ASC Topic 605, Revenue Recognition, or ASC 605. Accordingly, revenue is recognized for each unit of accounting when all of the following criteria are met:

•

Persuasive evidence of an arrangement exists;

•

Delivery has occurred or services have been rendered;

•

The seller’s price to the buyer is fixed or determinable; and

•

Collectability is reasonably assured.

Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion.

Revenue recognition from our MTPC collaboration commenced when the Company began to deliver the clinical supply of vadadustat to MTPC for use in MTPC’s Phase 3 studies of vadadustat in Japan which occurred in the fourth quarter of 2017. Therefore, collaboration revenue prior to the fourth quarter of 2017 is exclusively from the Company’s collaborations agreements with Otsuka. The terms of these arrangements contain multiple deliverables, which include at inception: (i) license, (ii) development services, (iii) rights to future intellectual property and (iv) joint committee services. Non-refundable payments to the Company under these arrangements include: (i) up-front fee, (ii) payments for development services and (iii) payments based on the achievement of certain milestones. Also, under the Otsuka U.S. Agreement, the Company and Otsuka share costs incurred with respect to jointly conducted medical affairs and commercialization and non-promotional activities under the collaboration. Additionally, the Company may receive its share of net sales and bear its share of shared costs from the sale of products containing or comprising vadadustat in the United States through its U.S. collaboration with Otsuka. With regards to the MTPC and Otsuka collaboration agreements, the Company recognizes revenue related to amounts allocated to the License Unit of Accounting on a proportional performance basis as the underlying services are performed.

The Company evaluates multiple‑element arrangements based on the guidance in ASC 605‑25. Pursuant to the guidance in ASC 605‑25, the Company evaluates multiple‑element arrangements to determine (i) the deliverables included in the arrangement and (ii) whether the individual deliverables represent separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires the Company to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in the Company’s control. In assessing whether an item has standalone value, the Company considers factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining deliverable(s), whether the value of the deliverable is dependent on the undelivered item and whether there are other vendors that can provide the undelivered item(s). The Company’s collaboration arrangements do not contain a general right of return relative to delivered item(s).

Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. The Company determines the selling price for a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determines the estimated selling price for units of accounting within each arrangement using vendor‑specific objective evidence (VSOE) of selling price, if available, third‑party evidence (TPE) of selling price if VSOE is not available, or best estimate of selling price (BESP) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity‑specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting.

The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. The Company recognizes as revenue arrangement consideration attributed to licenses that have standalone value from other deliverables to be provided in an arrangement upon delivery. The Company recognizes as revenue arrangement consideration attributed to licenses that do not have standalone value from the other deliverables to be provided in an arrangement over the contractual or estimated performance period associated with the undelivered elements included in the combined unit of accounting, which is typically the term of the Company’s development obligations. If there is no discernible pattern of performance and/or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight‑line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight‑line method or proportional performance method, as applicable, as of the period ending date.

The Company recognizes revenue associated with milestones in accordance with the provisions of ASC Topic 605-28, Revenue Recognition-Milestone Method. Accordingly, at the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are considered substantive are recognized as revenue in their entirety upon achievement, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive are recognized as revenue upon achievement if there are no remaining performance obligations or over the remaining period of performance if there are remaining performance obligations, assuming all other revenue recognition criteria are met. Revenue from commercial milestone payments will be accounted for as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.

The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.

Collaborative Arrangements

The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC Topic 808, Collaborative Arrangements, or ASC 808. Accordingly, the elements of the collaboration agreements that represent activities in which both parties are active participants and to which both parties are exposed to the significant risks and rewards that are dependent on the commercial success of the activities are recorded as collaborative arrangements. The Company considers the guidance in ASC Topic 605-45, Revenue Recognition—Principal Agent Considerations, or ASC 605-45, in determining the appropriate treatment for the transactions between the Company and its collaborative partner and the transactions between the Company and third parties. Generally, the classification of transactions under the collaborative arrangements is determined based on the nature and contractual terms of the arrangement along with the nature of the operations of the participants. The Company recognizes its allocation of the shared costs incurred with respect to the jointly conducted medical affairs and commercialization and non-promotional activities under the U.S. collaboration with Otsuka as a component of the related expense in the period incurred. During the year ended December 31, 2017, the Company incurred approximately $0.7 million of costs related to the cost-sharing provisions of the Otsuka U.S. Agreement of which approximately $0.2 million are reimbursable by Otsuka and recorded as a reduction to research and development expense during the year ended December 31, 2017. To the extent product revenue is generated from the collaboration, the Company will recognize its share of the net sales on a gross basis if it is deemed to be the principal in the transactions with customers, or on a net basis if it is instead deemed to be the agent in the transactions with customers, consistent with the guidance in ASC 605-45.

Patents

Costs incurred in connection with the application for and issuance of patents are expensed as incurred.

Research and Development Costs

Research and development costs are expensed as incurred.

Research and development expenses are comprised of costs incurred in providing research and development activities, including salaries and benefits, facilities costs, overhead costs, contract research and development services, and other outside costs. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.

External research and development expenses associated with the Company’s programs include clinical trial site costs, research compounds and clinical manufacturing costs, costs incurred for consultants and other outside services, such as data management and statistical analysis support, and materials and supplies used in support of the clinical and preclinical programs. Internal costs of the Company’s clinical program include salaries, benefits, stock-based compensation, and an allocation of the Company’s facility costs. When third-party service providers’ billing terms do not coincide with the Company’s period-end, the Company is required to make estimates of its obligations to those third parties, including clinical trial and pharmaceutical development costs, contractual services costs and costs for supply of its drug candidates, incurred in a given accounting period and record accruals at the end of the period. The Company bases its estimates on its knowledge of the research and development programs, services performed for the period, past history for related activities and the expected duration of the third-party service contract, where applicable.

Income Taxes

Income taxes are recorded in accordance with FASB Topic 740, Income Taxes, or ASC 740, which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. Valuation allowances are provided, if, based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. All deferred taxes as of December 31, 2017 and 2016 are classified as noncurrent within the income tax provision (see Note 9).

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position, as well as consideration of the available facts and circumstances. As of December 31, 2017 and 2016, the Company does not have any significant uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.

Stock-Based Compensation

The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation, or ASC 718. ASC 718 requires all stock-based payments to employees, including grants of employee stock options, restricted stock, restricted stock units, or RSUs, and modifications to existing stock awards, to be recognized in the statements of operations and comprehensive loss based on their fair values. The Company accounts for stock-based awards to non-employees in accordance with ASC Topic 505-50, Equity-Based Payments to Non-Employees, or ASC 505-50, which requires the fair value of the award to be re-measured at fair value until a performance commitment is reached or counterparty performance is complete. The Company’s stock-based awards are comprised of stock options, shares of restricted stock, shares of common stock and warrants. The Company estimates the fair value of options granted using the Black-Scholes option pricing model. The Company uses a blend of its stock price and the quoted market price of comparable public companies to determine the fair value of restricted stock awards and common stock awards.

The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of company-specific historical and implied volatility data for trading the Company’s stock in the public market, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. During 2017, the Company began to estimate its volatility by using a blend of its stock price history for the length of time it has market data for its stock and the historical volatility of similar public companies for the expected term of each grant. The Company is in the product development stage with no product revenue and the representative group of companies has certain similar characteristics to the Company. The Company believes the group selected has sufficient similar economic and industry characteristics and includes companies that are most representative of the Company. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term for options granted to employees as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post-vesting termination behavior among its employee population. For options granted to non-employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term assumption. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock, which is similar to the Company’s peer group.

The Company’s stock-based awards are subject to service based vesting conditions. Compensation expense related to awards to employees with service-based vesting conditions is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Consistent with the guidance in ASC 505- 50, compensation expense related to awards to non-employees with service-based vesting conditions is recognized on a straight-line basis based on the then-current fair value at each financial reporting date prior to the measurement date over the associated service period of the award, which is generally the vesting term.

The Company adopted ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, effective in the first quarter of the year ended December 31, 2017. Prior to adoption, share-based compensation expense was recognized on a straight-line basis, net of estimated forfeitures, such that expense was recognized only for share-based awards that are expected to vest. A forfeiture rate was estimated annually and revised, if necessary, in subsequent periods if actual forfeitures differed from initial estimates. Upon adoption, the Company no longer applies a forfeiture rate and instead will account for forfeitures as they occur.

Fair Value of Financial Instruments

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. ASC Topic 820, Fair Value Measurements and Disclosures, or ASC 820, establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available.

Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments, and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below:

•

Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

•

Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active, or for which all significant inputs are observable, either directly or indirectly.

•

Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Items measured at fair value on a recurring basis include short-term investments (see Note 5). The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The rate implicit within the Company’s capital lease obligation approximates market interest rates.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Cash, cash equivalents, investments, and accounts receivable are the only financial instruments that potentially subject the Company to concentrations of credit risk. The Company maintains its cash, cash equivalents, and investments with high quality, accredited financial institutions and, accordingly, such funds are subject to minimal credit risk. The Company’s investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentration of credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.

Accounts receivable represent amounts due from collaboration partners. The Company monitors economic conditions to identify facts or circumstances that may indicate that any of its accounts receivable are at risk of collection.

Net Loss per Share

Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the diluted net loss per share calculation, preferred stock, stock options, warrants, restricted stock and RSUs are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average shares outstanding for the period, including any dilutive effect from outstanding options, warrants, restricted stock and RSUs using the treasury stock method.

Property and Equipment

Property and equipment is stated at cost, less accumulated depreciation. Assets under capital lease are included in property and equipment. Property and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors, operating losses, unused capacity, market value declines and technological obsolescence. Recorded values of asset groups of equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale).

The following is the summary of property and equipment and related accumulated depreciation as of December 31, 2017 and 2016.

	Useful Life	December 31, 2017			December 31, 2016
		(in thousands)
Computer equipment and software	3	$	630		$	476
Furniture and fixtures	5		800			729
Equipment	7		628			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		2,582			1,763
Office equipment under capital lease	3		36			36
			4,676			3,054
Less accumulated depreciation			(1,059	)		(442	)
Net property and equipment		$	3,617		$	2,612

Depreciation expense, including expense associated with assets under capital leases, was approximately $616,000, $295,000 and $96,000 for the years ended December 31, 2017, 2016 and 2015, respectively.

Strategic Collaborations and Other Significant Agreements

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Strategic Collaborations and Other Significant Agreements

3. Strategic Collaborations and Other Significant Agreements

Mitsubishi Tanabe Pharma Corporation Collaboration Agreement

Summary of Agreement

On December 11, 2015, the Company and MTPC entered into a collaboration agreement, the MTPC Agreement, providing MTPC with exclusive development and commercialization rights to vadadustat in Japan and certain other Asian countries, collectively, the MTPC Territory. In addition, the Company will supply vadadustat for both clinical and commercial use in the MTPC Territory, subject to MTPC’s option to manufacture commercial drug product in the MTPC Territory.

The Company and MTPC agreed that, instead of including Japanese patients in the Company’s global Phase 3 program for vadadustat, MTPC would be the sponsor of a Phase 3 program for vadadustat in Japan. Following consultation with the Japanese Pharmaceuticals and Medical Devices Agency, or the PMDA, MTPC initiated its Phase 3 development program for vadadustat in Japan in the fourth quarter of 2017.

In consideration for the exclusive license and other rights contained in the MTPC Agreement, Japanese patients will not be included in the global Phase 3 program and MTPC will make payments totaling up to $265.0 million, comprised of $20.0 million upfront payment, up to $50.0 million in specified development and regulatory milestones, up to $175.0 million in specified commercial milestones, and $20.0 million for Phase 2 studies in Japanese patients completed by the Company and reimbursable by MTPC, as well as tiered double-digit royalty payments up to 20% on sales of vadadustat in the MTPC Territory.

MTPC is responsible for the costs of the Phase 3 program in Japan and other studies required there, and will make no funding payments for the global Phase 3 program. The Company recently completed its Phase 2 study of vadadustat in non-dialysis dependent, or NDD, Japanese patients and reported top-line data in the third quarter of 2017. The Company also announced top-line data on its Phase 2 study of vadadustat in dialysis-dependent, or DD, Japanese patients in Japan in the first quarter of 2018. The costs of these Phase 2 studies are reimbursable by MTPC. Therefore, of the $40.0 million received by the Company in 2016, $20.0 million related to the upfront payment and the remaining $20.0 million is being applied towards costs already incurred by the Company for the Phase 2 studies. In addition, MTPC will reimburse the Company for costs in excess of $20.0 million to complete the studies. The Company has incurred approximately $19.0 million in Phase 2 costs through December 2017 and anticipates incurring an additional approximately $2.4 million in Phase 2 costs through the end of the studies. As a result, MTPC would be required to reimburse the Company an additional approximately $1.4 million related to the two Phase 2 studies.

MTPC initiated a Phase 3 NDD-CKD study and a Phase 3 DD-CKD study in Japan in the fourth quarter of 2017. Pursuant to the terms of the MTPC Agreement, MTPC is responsible for performing all Phase 3 activities related to the development of vadadustat in the MTPC Territory and has sole responsibility for the commercialization of vadadustat in the MTPC Territory as well as for Medical Affairs (as defined in the MTPC Agreement) in the MTPC Territory. Akebia is responsible for the completion of Phase 2 dosing studies as reimbursed by MTPC, manufacturing and supplying vadadustat for clinical use in the MTPC Territory and, if approved by the FDA, will enter into a supply agreement with MTPC for the commercial supply of vadadustat prior to commercial launch.

The Company and MTPC have established a joint steering committee pursuant to the agreement to oversee development and commercialization of vadadustat in the MTPC Territory, including approval of any development or commercialization plans. Unless earlier terminated, the MTPC Agreement will continue in effect on a country-by-country basis until the later of: expiration of the last-to-expire patent covering vadadustat in such country in the MTPC Territory; expiration of marketing or regulatory exclusivity in such country in the MTPC Territory; or ten years after the first commercial sale of vadadustat in such country in the MTPC Territory. MTPC may terminate the MTPC Agreement upon twelve months’ notice at any time after the second anniversary of the effective date of the MTPC Agreement. Either party may terminate the MTPC Agreement upon the material breach of the other party that is not cured within a specified time period or upon the insolvency of the other party.

MTPC is required to make certain milestone payments to the Company aggregating to approximately $225.0 million upon the achievement of specified development, regulatory and commercial events. More specifically, the Company is eligible to receive up to $10.0 million in development milestone payments, up to $40.0 million in regulatory milestone payments for the first product to achieve the associated event and up to $175.0 million in commercial milestone payments associated with aggregate sales of all products. Additionally, if vadadustat is commercialized, the Company would be entitled to receive tiered royalty payments in the low double digits based on a percentage of net sales. Royalty payments are subject to certain reductions, including upon the introduction of competitive products in certain instances. Royalties are due on a country-by-country basis from the date of first commercial sale of a licensed product in a country until the last to occur of: (i) the expiration of the last to expire valid claim within the intellectual property covering the licensed product, (ii) the expiration of marketing or regulatory exclusivity in such country, or (iii) the tenth anniversary of the first commercial sale of such licensed product in such country. Due to the uncertainty of pharmaceutical development and the high historical failure rates associated with drug development, no milestone or royalty payments may ever be received from MTPC.

In September 2017, the Company and MTPC entered into a new agreement that provided MTPC with an option to access data from the Company’s global Phase 3 vadadustat program for payments to the Company of up to $25.0 million.

Revenue Recognition

The Company evaluated the elements of the MTPC Agreement in accordance with the provisions of ASC 605-25. The Company’s arrangement with MTPC contains the following deliverables: (i) license under certain of the Company’s intellectual property to develop and commercialize vadadustat in the MTPC Territory (the License Deliverable), (ii) clinical supply of vadadustat, (iii) knowledge transfer, (iv) Phase 2 dosing study research services, and (v) rights to future know-how.

The Company has identified two units of accounting in connection with its obligations under the MTPC Agreement. Factors considered in making the assessment of standalone value included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the value of the deliverable is dependent on the other elements in the arrangement, whether there are other vendors that can provide the items and if the customer could use the item for its intended purpose without the other deliverables in the arrangement. Additionally, the License Agreement does not include a general right of return. The two units of accounting identified in connection with the Company’s obligations under the MTPC Agreement are as follows:

(i)

License, Research Services and Clinical Supply Unit of Accounting

The License Deliverable does not have standalone value and does not qualify for separation from the clinical supply of vadadustat. More specifically, the license delivered to MTPC does not provide the contractual right to manufacture vadadustat. MTPC is contractually prohibited from manufacturing any Licensed Product covered by the licenses during clinical trials. Accordingly, MTPC must obtain the clinical trial products from the Company which significantly limits the ability for MTPC to use the license for their intended use on a standalone basis.

The License Deliverable does not have standalone value and does not qualify for separation from the knowledge transfer because MTPC cannot fully utilize the license for its intended purpose without the corresponding information regarding know-how, development data and regulatory materials possessed by the Company.

The License Deliverable does not have standalone value and does not qualify for separation from the Phase 2 dosing study research services because MTPC cannot fully utilize the license for its intended purpose without the performance of the Phase 2 dosing studies. The Phase 2 dosing studies needed to be performed prior to the PMDA approving any Phase 3 study to be performed in the MTPC Territory. Furthermore, MTPC cannot benefit from the Phase 2 dosing studies without the license and the undelivered Phase 3 clinical supply.

The License Deliverable does not have standalone value from the clinical supply, knowledge transfer or Phase 2 studies. As a result, the License Deliverable, clinical supply, knowledge transfer and Phase 2 studies have been combined as a single unit of accounting (the License, Research and Clinical Supply Unit of Accounting)

(ii)

Rights to Future Know-How Unit of Accounting

The License, Research and Clinical Supply Unit of Accounting has standalone value and qualifies for separation from the rights to future know how because MTPC can obtain the value of the License, Research and Clinical Supply Unit of Accounting without receipt of any rights to future know how that may be discovered or developed in the future.

The Company has determined that neither VSOE of selling price nor TPE of selling price is available for either of the units of accounting identified at inception of the arrangement with MTPC. Accordingly, the selling price of each unit of accounting was determined based on the Company’s BESP. The Company developed the BESP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company developed the BESP for the Rights to Future Know How Unit of Accounting primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement. The Company did not develop a BESP for the License, Research and Clinical Supply Unit of Accounting because the BESP associated with the Rights to Future Know How Unit of Accounting was determined to be immaterial. The Company has concluded that a change in the key assumptions used to determine the BESP for each unit of accounting would not have a significant impact on the allocation of arrangement consideration.

Allocable arrangement consideration at inception is comprised of: (i) the up-front payment of $20.0 million, (ii) the estimate of the cost for the Phase 2 studies of approximately $21.4 million, and (iii) the cost of all clinical supply provided to MTPC for the Phase 3 studies. No amounts were allocated to the Rights to Know How Unit of Accounting because the associated BESP was determined to be immaterial therefore the arrangement consideration will be allocated to the License, Research Services and Clinical Supply Unit of Accounting.

The Company has evaluated all of the development, regulatory and sales milestones that may be received in connection with the MTPC Agreement. In evaluating if a milestone is substantive, the Company assesses whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance, and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development and regulatory milestones, with the exception of one development milestone associated with the near-term progress of the Phase 3 study, are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. The non-substantive development milestone will be included in the arrangement consideration, if and when received, and allocated to the License, Research Services and Clinical Unit of Accounting within the arrangement and recognized as revenue when those underlying obligations are satisfied. The total aggregate amount of development milestones is $10.0 million, of which $6.0 million was received in December 2017 and the remaining $4.0 million was invoiced in January 2018, and the total aggregate amount of approval milestones is up to $40.0 million. All sales milestones, up to $175.0 million, will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.

Revenue for the fixed and determinable consideration made up of (i) the up-front payment of $20.0 million, (ii) the estimate of the cost for the Phase 2 studies of approximately $21.4 million, (iii) the cost of all clinical supply provided to MTPC for the Phase 3 studies, and (iv) $6.0 million in non-substantive development milestone received in the fourth quarter of 2017 will be recognized using a proportional performance method using the Company’s delivery of clinical supply of vadadustat to MTPC for the Phase 3 study as the basis. During the year-end December 31, 2017, the Company recognized revenue totaling $39.7 million with respect to the MTPC agreement. The revenue is classified as collaboration revenue in the accompanying consolidated statement of operations. As of December 31, 2017, there is approximately $7.5 million of short-term deferred revenue and $1.3 million in accounts receivable. There were no asset or liability balances classified as long-term in the consolidated balance sheet as of December 31, 2017.

U.S. Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd.

Summary of Agreement

On December 18, 2016, the Company entered into a collaboration and license agreement with Otsuka, or the Otsuka U.S. Agreement. The collaboration is focused on the development and commercialization of vadadustat in the United States. Under the terms of the Otsuka U.S. Agreement, the Company will continue to lead the development of vadadustat, including the ongoing Phase 3 development program. The Company and Otsuka will co-commercialize vadadustat in the United States, subject to the approval of vadadustat by the FDA.

Under the terms of the Otsuka U.S. Agreement, the Company granted to Otsuka a co-exclusive, non-sublicensable license under certain intellectual property controlled by the Company solely to perform medical affairs activities and to conduct non-promotional and commercialization activities related to vadadustat in accordance with the associated plans. The co-exclusive license relates to activities that will be jointly conducted by the Company and Otsuka pursuant to the terms of the Otsuka U.S. Agreement.

Pursuant to the terms of the Otsuka U.S. Agreement, the Company is responsible for performing all activities related to the development of vadadustat as outlined in the current global development plan. The current global development plan encompasses all activities with respect to the ongoing PRO₂TECT and INNO₂VATE clinical programs that are necessary through the filing for marketing approval, as well as other studies. Under the Otsuka U.S. Agreement, the Company controls and retains final decision‑making authority with respect to the development of vadadustat. The Company’s obligations related to the conduct of the current global development plan include the associated manufacturing and supply services for vadadustat.

Under the Otsuka U.S. Agreement, the parties jointly conduct, and have equal responsibility for, all medical affairs, commercialization and non-promotional activities pursuant to underlying plans as agreed to by the parties. If approved by the FDA, the Company will provide vadadustat to Otsuka for commercialization pursuant to a separate supply agreement to be negotiated.

The activities under the Otsuka U.S. Agreement are governed by a joint steering committee, or JSC, formed by an equal number of representatives from the Company and Otsuka. The JSC coordinates and monitors the parties’ activities under the collaboration. Among other responsibilities, the JSC manages the overall strategic alignment between the parties, oversees the current global development plan and reviews the other detailed plans setting forth the parties’ activities under the arrangement, including the medical affairs plan and commercialization and non-promotional activities plan. Additionally, the parties established a joint development committee, or JDC, which is comprised of an equal number of representatives from the Company and Otsuka. Among other responsibilities, the JDC will share information related to, and review and discuss activities and progress under, the current global development plan and any other development that may be conducted pursuant to the collaboration. In support of the potential commercialization of vadadustat, the parties will establish a joint commercialization committee, or JCC, which will be comprised of an equal number of representatives from the Company and Otsuka. Among other responsibilities, the JCC will manage the activities and progress under the commercialization and non-promotional activities plan and all other sales and marketing activities. The Company has retained the final decision‑making authority with respect to all development matters, pricing strategy and certain other key commercialization matters.

Under the terms of the Otsuka U.S. Agreement, the Company received a $125.0 million up-front, non-refundable, non-creditable cash payment in December 2016. In March 2017, the Company received a payment of approximately $33.8 million, which represents reimbursement for Otsuka’s share of costs previously incurred by the Company in implementing the current global development plan through December 31, 2016. Going forward, Otsuka will contribute a percentage of the remaining costs to be incurred under the current global development plan subsequent to December 31, 2016, commencing upon the date on which the Company has incurred a specified amount of incremental costs. The Company estimates that Otsuka’s funding of the current global development plan costs subsequent to December 31, 2016 will total $153.6 million or more, depending on the actual costs incurred toward the vadadustat global development program. The costs associated with the performance of any development activities in addition to those outlined in the current global development plan will be subject to a cost sharing or reimbursement mechanism to be determined by the parties. Costs incurred with respect to medical affairs and commercialization and non-promotional activities will generally be shared equally by the parties. Either party’s share of the medical affairs and/or commercialization activities may be increased at such party’s request upon mutual agreement of the parties. In addition, if the costs incurred in completing the activities under the current global development plan exceed a certain threshold, then the Company may elect to require Otsuka to fund a higher percentage of the current global development costs. In such event, the excess of the payments made under such election and Otsuka’s allocated share of the current global development costs is fully creditable against future payments due to the Company under the arrangement.

Under the Otsuka U.S. Agreement, the Company and Otsuka share the costs of developing and commercializing vadadustat in the United States and the profits from the sales of vadadustat after approval by the FDA. In connection with the profit share calculation, net sales include gross sales to third-party customers net of discounts, rebates, chargebacks, taxes, freight and insurance charges and other applicable deductions. Shared costs generally include costs attributable or reasonably allocable to the manufacture of vadadustat for commercialization purposes and the performance of medical affairs activities, non-promotional activities and commercialization activities.

Under the Otsuka U.S. Agreement, Otsuka originally had a limited period of time in which it can exercise an option to convert the arrangement from a profit share to a right to receive a mid-single digit royalty on future net sales of commercialized products (the Royalty Conversion Option). On August 4, 2017, Otsuka agreed to waive its right to exercise the Royalty Conversion Option in advance of its expiration, consequently, Otsuka has no further right to elect to exercise this option.

Unless earlier terminated, the Otsuka U.S. Agreement will expire on a country-by-country and product-by-product basis on the date that one or more generic versions of vadadustat first achieves 90% market penetration. Either party may terminate the Otsuka U.S. Agreement in its entirety upon an uncured breach or insolvency on the part of the other party. Otsuka may terminate the Otsuka U.S. Agreement in its entirety upon 12 months’ prior written notice at any time after the release of the first topline data from the global Phase 3 development program for vadadustat. In the event of termination of the Otsuka U.S. Agreement, all rights and licensees granted to Otsuka under the Otsuka U.S. Agreement will automatically terminate and the licenses granted to the Company will become freely sublicensable. In addition, the upfront payment, all development costs and milestone payments received by the Company prior to such termination will not be refunded to Otsuka.

Revenue Recognition

The Company evaluated the elements of the Otsuka US Agreement in accordance with the provisions of ASC 605-25. The Company’s arrangement with Otsuka contains the following deliverables: (i) license under certain of the Company’s intellectual property to develop, perform medical affairs activities with respect to and conduct non-promotional and commercialization activities related to vadadustat and products containing or comprising vadadustat (the License Deliverable), (ii) development services to be performed pursuant to the current global development plan (the Development Services Deliverable), (iii) rights to future intellectual property (the Future IP Deliverable), and (iv) joint committee services (the Committee Deliverable).

The Company has identified three units of accounting in connection with its obligations under the Otsuka U.S. Agreement. Factors considered in making the assessment of standalone value included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the value of the deliverable is dependent on the other elements in the arrangement, whether there are other vendors that can provide the items and if the customer could use the item for its intended purpose without the other deliverables in the arrangement. Additionally, the Otsuka U.S. Agreement does not include a general right of return. The three units of accounting identified in connection with the Company’s obligations under the Otsuka U.S. Agreement are as follows:

(i)

License and Development Services Combined (License Unit of Accounting)

The License Deliverable does not qualify for separation from the Development Services Deliverable, due to the contractual limitations inherent in the license conveyed. More specifically, Otsuka does not have the contractual right to manufacture vadadustat and products containing or comprising vadadustat. However, the manufacturing and supply services that are conducted as part of the services to be performed pursuant to the current global development plan are necessary for Otsuka to fully exploit the associated license for its intended purpose. The value of the rights provided through the license conveyed will be realized when the underlying products covered by the intellectual property progress through the development cycle, receive marketing approval and are commercialized. Products containing or comprising vadadustat cannot be commercialized until the development services under the current global development plan are completed. Accordingly, Otsuka must obtain the manufacturing and supply of the associated products that is included within the development services to be performed pursuant to the current global development plan from the Company in order to derive benefit from the license which significantly limits the ability for Otsuka to utilize the License Deliverable for its intended purpose on a standalone basis.

(ii)

Rights to Future Intellectual Property Unit of Accounting

The License Deliverable and the Development Services Deliverable qualify for separation from the Future IP Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development services without the receipt of any other intellectual property that may be discovered or developed in the future. The Future IP Deliverable qualifies for separation from the Committee Deliverable because the joint committee services have no bearing on the value to be derived from the rights to potential future intellectual property.

(iii)

Joint Committee Services Unit of Accounting

The License Deliverable and Development Services Deliverable qualify for separation from the Committee Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development services without the joint committee services. The Committee Deliverable has standalone value from the rights to Future IP Deliverable because the joint committee services have no bearing on the value to be derived from the rights to potential future intellectual property.

The Company has determined that neither VSOE of selling price nor TPE of selling price is available for any of the units of accounting identified at inception of the Otsuka U.S. Agreement. Accordingly, the selling price of each unit of accounting was determined based on the Company’s BESP. The Company developed the BESP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. In developing the BESP for the Joint Committee Services Unit of Accounting, the Company considered the nature of the services to be performed and estimates of the associated effort and rates applicable to such services that would be expected to be realized under similar contracts. The Company developed the BESP for the Rights to Future Intellectual Property Unit of Accounting primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement. The Company did not develop a BESP for the License Unit of Accounting due to the following: (i) the BESP associated with the Rights to Future Intellectual Property Unit of Accounting was determined to be immaterial and (ii) the period of performance and pattern of recognition for the License Unit of Accounting and the Joint Committee Services Unit of Accounting was determined to be similar. The Company has concluded that a change in the key assumptions used to determine the BESP for each unit of accounting would not have a significant impact on the allocation of arrangement consideration.

Allocable arrangement consideration at inception is comprised of: (i) the up-front payment of $125.0 million, (ii) the cost share payment with respect to amounts incurred by the Company through December 31, 2016 of $33.8 million, and (iii) an estimate of the cost share payments to be received with respect to amounts incurred by the Company subsequent to December 31, 2016. As of December 31, 2017, the estimate of the cost share payments to be received is $153.6 million or more. No amounts were allocated to the Rights to Future Intellectual Property Unit of Accounting because the associated BESP was determined to be immaterial. Due to the similar performance period and recognition pattern between the License Unit of Accounting and the Joint Committee Services Unit of Accounting, the arrangement consideration totaling $312.4 million has been allocated to the License Unit of Accounting and the Joint Committee Services Unit of Accounting on a combined basis. Accordingly, the Company will recognize revenue related to the allocable arrangement consideration on a proportional performance basis as the underlying development services are performed pursuant to the current global development plan which is commensurate with the period and consistent with the pattern over which the Company’s obligations are satisfied for both the License Unit of Accounting and the Joint Committee Services Unit of Accounting. Effectively, the Company has treated the arrangement as if the License Unit of Accounting and the Joint Committee Services Unit of Accounting are a single unit of accounting.

The Company has evaluated all of the development, regulatory and commercial milestones that may be received in connection with the Otsuka U.S. Agreement. In evaluating if a milestone is substantive, the Company assesses whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance, and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development and regulatory milestones are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.

During the years ended December 31, 2017 and December 31, 2016, the Company recognized revenue totaling approximately $86.0 million and $1.5 million, respectively, with respect to the Otsuka U.S. Agreement. The revenue is classified as collaboration revenue in the accompanying consolidated statement of operations. As of December 31, 2017, there is approximately $99.9 million of deferred revenue related to the Otsuka U.S. Agreement of which $45.3 million is classified as current and $54.6 million is classified as long-term in the accompanying consolidated balance sheet based on the performance period of the underlying obligations. Additionally, as of December 31, 2017, there is approximately $17.3 million in accounts receivable, of which $2.0 million is in unbilled accounts receivable, in the accompanying consolidated balance sheet.

The Company determined that the medical affairs, commercialization and non-promotional activities elements of the Otsuka U.S. Agreement represent joint operating activities in which both parties are active participants and of which both parties are exposed to significant risks and rewards that are dependent on the success of the activities. Accordingly, the Company is accounting for the joint medical affairs, commercialization and non-promotional activities in accordance with ASC No. 808, Collaborative Arrangements, or ASC 808. Additionally, the medical affairs, commercialization and non-promotional activities were not deemed to be deliverables under ASC No. 605-25, Revenue Recognition–Multiple-Element Arrangements, or ASC 605-25. As a result, the activities conducted pursuant to the medical affairs, commercialization and non-promotional activities plans will be accounted for as a component of the related expense in the period incurred. During the year ended December 31, 2017, the Company incurred approximately $0.7 million of costs related to the cost-sharing provisions of the Otsuka U.S. Agreement of which approximately $0.2 million are reimbursable by Otsuka and recorded as a reduction to research and development expense during the year ended December 31, 2017.

International Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd.

Summary of Agreement

On April 25, 2017, the Company entered into a collaboration and license agreement with Otsuka, or the Otsuka International Agreement. The collaboration is focused on the development and commercialization of vadadustat in Europe, Russia, China, Canada, Australia, the Middle East and certain other territories, collectively, the Otsuka International Territory. Under the terms of the Otsuka International Agreement, the Company will continue to lead the development of vadadustat, including the ongoing global Phase 3 development program. Otsuka has the sole responsibility, at its own cost, for the commercialization of vadadustat in the Otsuka International Territory, subject to the approval by the relevant regulatory authorities.

Under the terms of the Otsuka International Agreement, the Company granted to Otsuka an exclusive, sublicensable license under certain intellectual property controlled by the Company to develop and commercialize vadadustat and products containing or comprising vadadustat in the Otsuka International Territory.

Pursuant to the terms of the Otsuka International Agreement, the Company is responsible for performing all activities related to the development of vadadustat as outlined in the current global development plan; however, the parties may agree to allocate certain responsibilities to Otsuka. The current global development plan encompasses all activities with respect to the ongoing PRO₂TECT and INNO₂VATE program, as well as other studies, through the filing for marketing approval. The current global development plan also includes other derivative and ancillary studies. Under the Otsuka International Agreement, the Company controls and retains final decision-making authority with respect to the development of vadadustat other than with respect to certain development matters specific to the Otsuka International Territory. Per the terms of the Otsuka International Agreement, Otsuka is generally responsible for the conduct of any development activities that may be required for marketing approval in the Otsuka International Territory or otherwise performed with respect to the Otsuka International Territory that are incremental to those included in the current global development plan. The Company’s obligations related to the conduct of the current global development plan include the associated manufacturing and supply services for vadadustat.

Under the Otsuka International Agreement, Otsuka is to be solely responsible for the conduct of all medical affairs and commercialization activities in the Otsuka International Territory pursuant to underlying plans as reviewed and discussed by the parties. If approved by the relevant jurisdictional regulatory health authorities in the Otsuka International Territory, the Company will provide vadadustat to Otsuka for commercialization pursuant to a separate supply agreement to be negotiated.

The activities under the Otsuka International Agreement are governed by a JSC formed by up to a specified number of representatives from the Company and Otsuka. The JSC coordinates and monitors the parties’ activities under the collaboration. Among other responsibilities, the JSC manages the overall strategic alignment between the parties, oversees the current global development plan and reviews the other detailed plans setting forth any other development activities that may be conducted under the arrangement. Additionally, the parties established a JDC which is be comprised of up to a specified number of representatives from the Company and Otsuka. Among other responsibilities, the JDC shares information related to, and reviews and discusses activities and progress under, the current global development plan and any other development that may be conducted pursuant to the collaboration. The Company and Otsuka also established a joint manufacturing committee, or JMC, which is comprised of up to a specified number of representatives from each of the parties. Among other responsibilities, the JMC oversees the manufacturing plan and related manufacturing activities. In support of the potential commercialization of vadadustat, the parties established a JCC which is comprised of up to a specified number of representatives from the Company and Otsuka. Among other responsibilities, the JCC reviews and discusses the activities and progress under the commercialization plan and all other sales and marketing activities. The Company has retained the final decision‑making authority with respect to all development matters, other than decisions related to certain development matters specific to the Otsuka International Territory. Otsuka has retained the final decision‑making authority with respect to all commercialization matters, other than decisions related to certain marketing matters.

Under the terms of the Otsuka International Agreement, the Company received a $73.0 million up-front, non-refundable, non-creditable cash payment. The Company also received a payment of approximately $0.2 million which represents reimbursement for Otsuka’s share of costs previously incurred by the Company in implementing the current global development plan in excess of a specified threshold during the quarter-ended March 31, 2017. Additionally, Otsuka will contribute a percentage of the remaining costs to be incurred under the current global development plan subsequent to March 31, 2017. The Company estimates that Otsuka’s funding of the current global development plan costs subsequent to March 31, 2017 will total roughly $163.6 million or more, depending on the actual global development costs incurred. The costs associated with the performance of any mutually agreed upon development activities in addition to those outlined in the current global development plan will be subject to a cost sharing or reimbursement mechanism to be determined by the parties. Otsuka may elect to conduct additional studies of vadadustat in the EU, subject to the Company’s right to delay such studies based on its objectives outside the Otsuka International Territory. Otsuka will pay a percentage of the costs of any such studies, and the Company will pay its portion of the costs in the form of a credit against future amounts due to the Company under the Otsuka International Agreement. The costs incurred related to any other development activities, which are pursued solely for obtaining or maintaining marketing approval in the Otsuka International Territory or otherwise performed solely with respect to the Otsuka International Territory that are incremental to the development activities included in the current global development plan, will be borne in their entirety by Otsuka. Otsuka will pay costs incurred with respect to medical affairs and commercialization activities in the Otsuka International Territory.

In addition, Otsuka would be required to make certain milestone payments to the Company upon the achievement of specified development, regulatory and commercial events. More specifically, the Company is eligible to receive up to $80.0 million in development milestone payments and up to $52.0 million in regulatory milestone payments for the first product to achieve the associated event. Moreover, the Company is eligible for up to $525.0 million in commercial milestone payments associated with aggregate sales of all products. Additionally, to the extent vadadustat is commercialized, the Company would be entitled to receive tiered royalty payments ranging from the low double digits to the low thirties based on a percentage of net sales. Royalties are due on a country-by-country basis from the date of the first commercial sale of a licensed product in a country until the latest to occur of: (i) the expiration date in such country of the last to expire valid claim within the intellectual property covering the licensed product, (ii) the date of expiration of data or regulatory exclusivity in such country or (iii) the tenth anniversary of the first commercial sale of such licensed product in such country. Due to the uncertainty of pharmaceutical development and the high historical failure rates associated therewith, no milestone or royalty payments may ever be received from Otsuka. There are no cancellation, termination or refund provisions in the Otsuka International Agreement that contain material financial consequences to the Company.

Unless earlier terminated, the Otsuka International Agreement will expire upon the expiration of the royalty term in the last country in the Otsuka International Territory. Either party may terminate the Otsuka International Agreement in its entirety upon an uncured material breach or insolvency on the part of the other party. Otsuka may terminate the Otsuka International Agreement in its entirety or for a specific sub-division of the Otsuka International Territory upon 12 months’ prior written notice at any time after the release of the first topline data from either the PRO₂TECT Phase 3 development program or the INNO₂VATE Phase 3 development program, whichever comes first. In the event of termination of the Otsuka International Agreement, all rights and licensees granted to Otsuka under the Otsuka International Agreement will automatically terminate and the licenses granted to the Company will become freely sublicensable, but potentially subject to a future royalty. In addition, the upfront payment, all development costs and milestone payments received by the Company prior to such termination will not be eligible for refund to Otsuka.

Revenue Recognition

The Company has accounted for the Otsuka International Agreement separately from the collaboration arrangement with Otsuka with respect to the U.S. due to the lack of interrelationship and interdependence of the elements and payment terms within each of the contracts as it relates to the respective territories. Accordingly, the Company has applied the guidance in ASC No. 605-25, Revenue Recognition–Multiple-Element Arrangements, or ASC 605-25, solely in reference to the terms and conditions of the Otsuka International Agreement, while the collaboration arrangement with Otsuka related to the U.S. has continued to be accounted for as a discrete agreement in its own right. The Company evaluated the Otsuka International Agreement in accordance with the provisions of ASC 605-25. The Company’s arrangement with Otsuka related to the Otsuka International Territory contains the following deliverables: (i) license under certain of the Company’s intellectual property to develop and commercialize (including the associated packaging) vadadustat and products containing or comprising vadadustat (the License Deliverable), (ii) development services to be performed pursuant to the current global development plan (the Development Services Deliverable), (iii) rights to future intellectual property (the Future IP Deliverable) and (iv) joint committee services (the Committee Deliverable).

The Company has identified three units of accounting in connection with its obligation under the Otsuka International Agreement. Factors considered in making this assessment included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the value of the deliverable is dependent on the other elements in the arrangement, whether there are other vendors that can provide the items and if the customer could use the item for its intended purpose without the other deliverables in the arrangement. Additionally, the Otsuka International Agreement does not include a general right of return. The three units of accounting identified in connection with the Company’s obligations under the Otsuka International Agreement are as follows:

(i)

License and Development Services Combined (License Unit of Accounting)

The License Deliverable does not qualify for separation from the Development Services Deliverable due to the contractual limitations inherent in the license conveyed. More specifically, Otsuka does not have the contractual right to manufacture vadadustat and products containing or comprising vadadustat. However, the manufacturing and supply services that are conducted as part of the services to be performed pursuant to the current global development plan are necessary for Otsuka to fully exploit the associated license for its intended purpose. The value of the rights provided through the license conveyed will be realized when the underlying products covered by the intellectual property progress through the development cycle, receive marketing approval and are commercialized. Products containing or comprising vadadustat cannot be commercialized until the development services under the current global development plan are completed. Accordingly, Otsuka must obtain the manufacturing and supply of the associated products that is included within the development services to be performed pursuant to the current global development plan from the Company in order to derive benefit from the license which significantly limits the ability for Otsuka to utilize the License Deliverable for its intended purpose on a standalone basis. Therefore, the License Deliverable does not have standalone value from the Development Services Deliverable. As a result, the License Deliverable and the Development Services Deliverable have been combined as a single unit of accounting (the License Unit of Accounting).

(ii)

Rights to Future Intellectual Property Unit of Accounting

The License Deliverable and the Development Services Deliverable qualify for separation from the Future IP Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development services without the receipt of any other intellectual property that may be discovered or developed in the future. The Future IP Deliverable qualifies for separation from the Committee Deliverable because the Committee Services Deliverable has no bearing on the value to be derived from the rights to potential future intellectual property.

(iii)

Joint Committee Services Unit of Accounting

The License Deliverable and the Development Services deliverable qualify for separation from the Committee Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development service without the joint committee services. The Committee Deliverable qualifies for separation from the Future IP Deliverable because the Committee Deliverable has no bearing on the value to be derived from the rights to potential future intellectual property.

The Company has determined that neither VSOE of selling price nor TPE of selling price is available for any of the units of accounting identified at inception of the arrangement with Otsuka. Accordingly, the selling price of each unit of accounting was determined based on the Company’s BESP. The Company developed the BESP with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. In developing the BESP for the Joint Committee Services Unit of Accounting, the Company considered the nature of the services to be performed and estimates of the associated effort and rates applicable to such services that would be expected to be realized under similar contracts. The Company developed the BESP for the Rights to Future Intellectual Property Unit of Accounting primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement. The Company did not develop a BESP for the License Unit of Accounting due to the following: (i) the BESP associated with the rights to future intellectual property unit of accounting was determined to be immaterial and (ii) the period of performance and pattern of recognition for the License Unit of Accounting and the joint committee services unit of accounting was determined to be similar. The Company has concluded that a change in the key assumptions used to determine the BESP for each unit of accounting would not have a significant impact on the allocation of arrangement consideration.

Allocable arrangement consideration at inception is comprised of: (i) the up-front payment of $73.0 million, (ii) the cost share payment with respect to amounts incurred by the Company during the quarter ended March 31, 2017 of $0.2 million and (iii) an estimate of the cost share payments to be received with respect to amounts incurred by the Company subsequent to March 31, 2017. As of December 31, 2017, the estimate of the cost share payments to be received is approximately $163.6 million. No amounts were allocated to the Rights to Future Intellectual Property Unit of Accounting because the associated BESP was determined to be immaterial. Due to the similar performance period and recognition pattern between the License Unit of Accounting and the Joint Committee Services Unit of Accounting, the arrangement consideration totaling $236.8 million has been allocated to the License Unit of Accounting and the Joint Committee Services Unit of Accounting on a combined basis. Accordingly, the Company will recognize revenue related to the allocable arrangement consideration on a proportional performance basis as the underlying development services are performed pursuant to the current global development plan which is commensurate with the period and consistent with the pattern over which the Company’s obligations are satisfied for both the License Unit of Accounting and the Joint Committee Services Unit of Accounting. Effectively, the Company has treated the arrangement as if the License Unit of Accounting and the Joint Committee Services Unit of Accounting are a single unit of accounting.

The Company has evaluated all of the development, regulatory and commercial milestones that may be received in connection with the Otsuka International Agreement. In evaluating if a milestone is substantive, the Company assesses whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance, and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development and regulatory milestones are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.

During the year ended December 31, 2017, the Company recognized revenue totaling approximately $52.3 million with respect to the Otsuka International Agreement. The revenue is classified as collaboration revenue in the accompanying consolidated statement of operations. As of December 31, 2017, there is approximately $70.8 million of deferred revenue related to the Otsuka International Agreement of which $32.1 million is classified as current and $38.7 million is classified as long-term in the accompanying consolidated balance sheet based on the performance period of the underlying obligations. Additionally, as of December 31, 2017, there is approximately $15.6 million in accounts receivable, of which $1.7 million is in unbilled accounts receivable, in the accompanying consolidated balance sheet.

Janssen Pharmaceutica NV Research and License Agreement

Summary of Agreement

On February 9, 2017, the Company entered into a Research and License Agreement, the Janssen Agreement, with Janssen Pharmaceutica NV, or Janssen, a subsidiary of Johnson & Johnson, pursuant to which Janssen granted the Company an exclusive license under certain intellectual property rights to develop and commercialize worldwide certain HIF-PH targeted compounds.

Under the terms of the Janssen Agreement, Janssen granted to the Company a license for a three-year research term to conduct research on the HIF compound portfolio, unless the Company elects to extend such research term for up to two additional one-year periods upon payment of an extension fee. During the research term, the Company may designate one or more compounds as candidates for development and commercialization. Once a compound is designated for development and commercialization, the Company will be solely responsible for the development and commercialization of the compound worldwide at its own cost and expense. The Janssen Agreement includes a license to develop and commercialize AKB-5169, a preclinical compound in development as an oral treatment for inflammatory bowel disease, or IBD.

Under the terms of the Janssen Agreement, the Company made an upfront payment of $1.0 million in cash to Janssen and issued a warrant to purchase 509,611 shares of the Company’s common stock. In addition, Janssen could be eligible to receive up to an aggregate of $16.5 million from the Company in specified development milestone payments on a product-by-product basis. Janssen will also be eligible to receive up to $215.0 million from the Company in specified commercial milestones as well as tiered, escalating royalties ranging from a low to mid-single digit percentage of net sales, on a product-by-product basis.

Unless earlier terminated, the Janssen Agreement will expire on a product-by-product and country-by-country basis upon the expiration of the last royalty term, which ends upon the longer of the expiry of the patents licensed under the Janssen Agreement, the expiry of regulatory exclusivity for such product, or 10 years from first commercial sale of such product. The Company may terminate the Janssen Agreement in its entirety or only with respect to a particular licensed compound or product upon 180 days’ prior written notice to Janssen. The parties also have customary termination rights, subject to a cure period, in the event of the other party’s material breach of the Janssen Agreement or in the event of certain additional circumstances.

As discussed above, the Company issued a Common Stock Purchase Warrant, the Warrant, to Johnson & Johnson Innovation – JJDC, Inc., or JJDC, an affiliate of Janssen, for 509,611 shares of the Company’s common stock at an exercise price of $9.81 per share. The Warrant is exercisable by JJDC, in whole or in part, at any time prior to the fifth anniversary of the date of issuance. The Warrant and the shares issuable upon exercise of the Warrant will be sold and issued without registration under the Securities Act of 1933, or the Securities Act. The Company recorded the fair value of the warrant in the amount of $3.4 million to additional paid in capital and research and development expense in March 2017.

Vifor Pharma License Agreement

Summary of License Agreement

On May 12, 2017, the Company entered into a License Agreement, or the Vifor Agreement, with Vifor (International) Ltd., or Vifor Pharma, pursuant to which the Company will grant Vifor Pharma an exclusive license to sell vadadustat solely to Fresenius Kidney Care Group LLC, or FKC, an affiliate of Fresenius Medical Care North America, in the United States.

The parties’ rights under the Vifor Agreement are conditioned upon the approval of vadadustat for DD-CKD patients by the FDA, inclusion of vadadustat in a bundled reimbursement model, and payment by Vifor Pharma of a $20.0 million milestone upon the occurrence of these two events. The Vifor Agreement is structured as a profit share arrangement between the Company and Vifor Pharma in which the Company will receive a majority of the profit from Vifor Pharma’s sales of vadadustat to FKC in the United States. The Company will share the milestone payment and the revenue from the profit share with Otsuka pursuant to the Otsuka U.S Agreement. The Company retains all rights to commercialize vadadustat for use in the NDD-CKD market and in other dialysis organizations in the United States, which will be done in collaboration with Otsuka following FDA approval.

Prior to FDA approval of vadadustat, the Company and Vifor Pharma will enter into a commercial supply agreement for vadadustat pursuant to which the Company will supply all of Vifor Pharma’s requirements for vadadustat in the United States. In addition, Vifor Pharma will enter into a supply agreement with FKC that will govern the terms pursuant to which Vifor Pharma will supply vadadustat to FKC for use in patients at its dialysis centers. During the term of the Vifor Agreement, Vifor Pharma will not sell to FKC or its affiliates any HIF product that competes with vadadustat in the United States.

Unless earlier terminated, the Vifor Agreement will expire upon the later of the expiration of all patents that claim or cover vadadustat, or expiration of data or regulatory exclusivity for vadadustat in the United States. Vifor Pharma may terminate the Vifor Agreement in its entirety upon 12 months’ prior written notice after the release of the first topline data in the vadadustat global Phase 3 program for dialysis-dependent CKD patients. Either party may terminate the Vifor Agreement in the event of the other party’s uncured material breach. The Company may also terminate the Vifor Agreement upon the occurrence of other events, such as for specific violations of the Vifor Agreement or if there are changes in Vifor Pharma’s relationship with FKC.

Investment Agreement

In connection with the Vifor Agreement, in May 2017, the Company and Vifor Pharma entered into an investment agreement, the Investment Agreement, pursuant to which the Company sold an aggregate of 3,571,429 shares of common stock, the Shares, par value $0.00001 per share, to Vifor Pharma at a price per share of $14.00 for a total of $50.0 million dollars. The amount representing the premium over the closing stock price of $12.69 on the date of the transaction, totaling $4.7 million, was determined by the Company to represent consideration related to the Vifor Agreement. As the parties’ rights under the Vifor Agreement are conditioned upon (a) the approval of vadadustat for DD-CKD patients by the FDA; (b) inclusion of vadadustat in a bundled reimbursement model; and (c) payment by Vifor Pharma of a $20.0 million milestone upon the occurrence of these two events, in accordance with ASC 605, the Company cannot currently determine the extent of its responsibility to supply all of Vifor Pharma’s requirements for vadadustat in the United States. Accordingly, the $4.7 million is recorded as deferred revenue in the accompanying consolidated balance sheets. Upon the satisfaction of the aforementioned conditions, revenue will be recognized as the Company supplies vadadustat to Vifor Pharma using a proportional performance method.

Vifor Pharma has agreed to a lock-up restriction such that it agrees not to sell its shares for a period of time following the effective date of the Investment Agreement as well as a customary standstill agreement. In addition, the Investment Agreement contains voting agreements made by Vifor Pharma with respect to the Shares. The Shares have not been registered pursuant to Securities Act of 1933, the “Act”, and were issued and sold in reliance upon the exemption from registration contained in Section 4(a)(2) of the Act and Rule 506 promulgated thereunder.

Available for Sale Securities

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Available for Sale Securities

4. Available for Sale Securities

Available for sale securities at December 31, 2017 and 2016 consist of the following:

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2017
Cash and cash equivalents	$	70,156	$	—	$	—		$	70,156
Available for sale securities:
Certificates of deposit	$	14,117	—		—			$	14,117
U.S. government debt securities		175,155	—			(352	)		174,803
Corporate debt securities		58,806	—			(90	)		58,716
Total available for sale securities	$	248,078	$	—	$	(442	)	$	247,636
Total cash, cash equivalents, and available for sale securities	$	318,234	$	—	$	(442	)	$	317,792

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2016
Cash and cash equivalents	$	187,335	$	—	$	—		$	187,335
Available for sale securities:
Certificates of deposit	$	12,698	—			—		$	12,698
U.S. government debt securities		50,952	—			(32	)		50,920
Corporate debt securities		9,398	—			(8	)		9,390
Total available for sale securities	$	73,048	$	—	$	(40	)	$	73,008
Total cash, cash equivalents, and available for sale securities	$	260,383	$	—	$	(40	)	$	260,343

The estimated fair value of the Company’s available for sale securities balance at December 31, 2017, by contractual maturity, is as follows:

Due in one year or less	$	217,884
Due after one year		29,752
Total available for sale securities	$	247,636

There were no realized gains or losses on available for sale securities for the years ended December 31, 2017 or 2016. There were three U.S. government debt securities that had been in an unrealized loss position for more than 12 months as of December 31, 2017 with an aggregate unrealized loss on these securities of $9,000 and fair value of $4.0 million. There were no available for sale securities that had been in an unrealized position for more than 12 months as of December 31, 2016. There were 57 securities in a loss position for less than 12 months at December 31, 2017 with an aggregate unrealized loss on these securities of $433,000 and fair value of $229.5 million. There were 27 securities in a loss position for less than 12 months at December 31, 2016 with an aggregate unrealized loss on these securities of $40,000 and fair value of $60.3 million. The Company considered the decline in the market value of these securities to be primarily attributable to current economic conditions. The contractual terms of these securities do not permit the issuer to settle the securities at a price less than the amortized cost basis of the investment. As it was not more likely than not that the Company would be required to sell these securities before the recovery of their amortized cost basis, which may be at maturity, the Company did not consider these investments to be other-than-temporarily impaired as of December 31, 2017.

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

5. Fair Value of Financial Instruments

The Company utilizes a portfolio management company for the valuation of the majority of its investments. This company is an independent, third-party vendor recognized to be an industry leader with access to market information that obtains or computes fair market values from quoted market prices, pricing for similar securities, recently executed transactions, cash flow models with yield curves and other pricing models. For valuations obtained from the pricing service, the Company performs due diligence to understand how the valuation was calculated or derived, focusing on the valuation technique used and the nature of the inputs.

Based on the fair value hierarchy, the Company classifies its cash equivalents and available for sale securities within Level 1 or Level 2. This is because the Company values its cash equivalents and available for sale securities using quoted market prices or alternative pricing sources and models utilizing market observable inputs.

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2017 and December 31, 2016 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2017
Assets:
Cash and cash equivalents	$	70,156	$	—	$	—	$	70,156
Certificates of deposit		—		14,117		—		14,117
U.S. government debt securities		—		174,803		—		174,803
Corporate debt securities		—		58,716		—		58,716
	$	70,156	$	247,636	$	—	$	317,792

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2016
Assets:
Cash and cash equivalents	$	187,335	$	—	$	—	$	187,335
Certificates of deposit		—		12,698		—		12,698
U.S. government debt securities		—		50,920		—		50,920
Corporate debt securities		—		9,390		—		9,390
	$	187,335	$	73,008	$	—	$	260,343

The Company’s corporate debt securities are all investment grade.

The Company had no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) at December 31, 2017 and December 31, 2016.

Investment securities are exposed to various risks such as interest rate, market and credit. Due to the level of risk associated with certain investment securities and the level of uncertainty related to changes in the value of investment securities, it is at least reasonably possible that changes in risks in the near term would result in material changes in the fair value of investments.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Accrued Expenses

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Accrued Expenses

6. Accrued Expenses

Accrued expenses are as follows:

	December 31, 2017		December 31, 2016
	(in thousands)
Accrued clinical	$	43,297	$	23,643
Accrued bonus		3,388		2,995
Income tax payable		987		—
Professional fees		808		539
Accrued vacation		797		513
Accrued payroll		795		596
Accrued severance		—		29
Other		2,369		1,946
Total accrued expenses	$	52,441	$	30,261

Stockholders' Equity

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Stockholders' Equity

8. Stockholders’ Equity

Authorized and Outstanding Capital Stock

As of December 31, 2017, the authorized capital stock of the Company included 175,000,000 shares of common stock, par value $0.00001 per share, of which 47,612,619 and 38,615,709 shares were issued and outstanding at December 31, 2017 and 2016, respectively; and 25,000,000 shares of undesignated preferred stock, par value $0.00001 per share, of which 0 shares were issued and outstanding at December 31, 2017 and December 31, 2016.

On March 6, 2014, the Company effected a 1.75-for-1 stock split of its outstanding common stock. Unless otherwise indicated, all share data and per share amounts in these financial statements have been retroactively adjusted to reflect the stock split, as well as any stock splits that occurred in periods prior to March 6, 2014.

Upon the closing of the IPO on March 25, 2014, all of the outstanding shares of the Company’s redeemable convertible preferred stock were converted into 12,115,183 shares of its common stock. As of December 31, 2014, the Company does not have any redeemable convertible preferred stock issued or outstanding.

At-the-Market Facility

In May 2016, the Company established an at-the-market equity offering program pursuant to which it was able to offer and sell up to $75.0 million its common stock at the then current market prices from time to time. In September 2016, the Company commenced sales under this program. During the years ended December 31, 2017 and 2016, the Company sold 465,615 and 615,293 shares of common stock, respectively, under this program with net proceeds (after deducting commissions and other offering expenses) of $6.4 million and $5.7 million, respectively.

From January 1, 2018 through March 12, 2018, the Company sold 694,306 shares of common stock under the at-the-market offering program with net proceeds (after deducting commissions and other offering expenses) of $10.5 million.

Equity Plans

On February 28, 2014, the Company’s Board of Directors adopted its 2014 Incentive Plan (the “2014 Plan”) and its 2014 Employee Stock Purchase Plan (the “ESPP”), which were subsequently approved by its stockholders and became effective upon the closing of the Company’s initial public offering on March 25, 2014. The 2014 Plan replaced the 2008 Equity Incentive Plan (as amended, the “2008 Plan”); however, options or other awards granted under the 2008 Plan prior to the adoption of the 2014 Plan that have not been settled or forfeited remain outstanding and effective. In May 2016 the Company’s Board of Directors approved an inducement award program that was separate from the Company’s equity plans and which, consistent with NASDAQ Listing Rule 5635(c)(4), did not require shareholder approval (the “2016 Inducement Award Program”). In 2017, the Company authorized the issuance of up to 700,000 shares for new hires under the 2016 Inducement Award Program, of which 525,500 stock options were granted during the year. At December 31, 2017, 508,500 stock options granted in 2017 under the 2016 Inducement Award Program remain eligible to vest.

The 2014 Plan allows for the granting of stock options, stock appreciation rights (SARs), restricted stock, unrestricted stock, restricted stock units (RSUs), performance awards and other awards convertible into or otherwise based on shares of our common stock. Dividend equivalents may also be provided in connection with an award under the 2014 Plan. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2014 Plan. The Company initially reserved 1,785,000 shares of its common stock for the issuance of awards under the 2014 Plan. The 2014 Plan provides that the number of shares reserved and available for issuance under the 2014 Plan will automatically increase annually on January 1^st of each calendar year, by an amount equal to three percent (3%) of the number of shares of stock outstanding on a fully diluted basis as of the close of business on the immediately preceding December 31^st(the “2014 Plan Evergreen Provision”). The Company’s Board of Directors may act prior to January 1^st of any year to provide that there will be no automatic increase in the number of shares available for grant under the 2014 Plan for that year (or that the increase will be less than the amount that would otherwise have automatically been made). During the year ended December 31, 2017, the Company granted 719,400 stock options to employees under the 2014 Plan, 525,500 stock options to employees under the 2016 Inducement Award Program, 449,900 restricted stock units (RSUs) to employees under the 2014 Plan, and 87,500 stock options to directors under the 2014 Plan.

The ESPP provides for the issuance of options to purchase shares of the Company’s common stock to participating employees at a discount to their fair market value. The maximum aggregate number of shares of common stock available for purchase pursuant to the exercise of options granted under the ESPP will be the lesser of (a) 262,500 shares, increased on each anniversary of the adoption of the ESPP by one percent (1%) of the total shares of common stock then outstanding (the “ESPP Evergreen Provision”) and (b) 739,611 shares (which is equal to five percent (5%) of the total shares of common stock outstanding on the date of the adoption of the ESPP on a fully diluted, as converted basis. Under the ESPP, each offering period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering. The per-share purchase price at the end of each offering period is equal to the lesser of eighty-five percent (85%) of the closing price of our common stock at the beginning or end of the offering period.

Shares Reserved for Future Issuance

The Company has reserved for future issuance the following number of shares of common stock:

	December 31, 2017		December 31, 2016
Common stock options and RSU's outstanding ⁽¹⁾		4,388,752		3,579,694
Shares available for issuance under the 2014 Plan ⁽²⁾		1,790,600		1,140,328
Warrant to purchase common stock		509,611		—
Shares available for issuance under the ESPP ⁽³⁾		652,290		803,105
Total		7,341,253		5,523,127

⁽¹⁾

Includes awards granted under the 2014 Plan and the 2016 Inducement Award Program.

⁽²⁾

On January 1, 2018, January 1, 2017 and January 1, 2016, the shares reserved for future grants under the 2014 Plan increased by 1,575,329, 1,265,863 and 986,800 shares, respectively, pursuant to the 2014 Plan Evergreen Provision. On December 19, 2017, the Company’s Board of Directors approved 750,000 shares to become available for issuance effective January 1, 2018 under the 2016 Inducement Award Program. As these shares are not available for issuance as of year-end, they have been excluded from the table above.

⁽³⁾

On February 28, 2017 and February 28, 2016, the shares reserved for future issuance under the ESPP increased by 0 and 273,404 shares, respectively, pursuant to the ESPP Evergreen Provision.

Stock-Based Compensation

Stock Options

On February 21, 2017, as part of the Company’s annual grant of equity, the Company issued 719,400 stock options to employees. In addition, the Company issues stock options to new hires and occasionally to other employees not in connection with the annual grant process. Options granted by the Company vest over periods of between 12 and 48 months, subject, in each case, to the individual’s continued service through the applicable vesting date. Options vest in installments of (i) 25% at the one year anniversary and (ii) in either 36 or 48 equal monthly installments beginning in the thirteenth month after the initial vesting commencement date or 12 equal quarterly installments beginning on the first day of each calendar quarter after the initial vesting commencement date or grant date, subject to the individual’s continuous service with the Company. Options generally expire ten years after the date of grant. The Company recorded approximately $6.5 million and $4.7 million of stock-based compensation expense related to stock options during 2017 and 2016, respectively.

The assumptions used in the Black-Scholes pricing model to estimate the grant date fair value of options granted to employees are as follows:

	Year ended December 31,
	2017	2016		2015
Risk-free interest rate	1.81% - 2.27%	1.16% - 2.03%		1.44% - 1.95%
Dividend yield	0.00%		0.00%		0.00%
Volatility	78.57% - 85.81%	64.78% - 82.40%		62.47% - 81.25%
Expected term (years)	5.51 - 6.25	5.51 - 6.25		5.51 - 6.25

The following table summarizes the Company’s stock option activity for the year ended December 31, 2017:

	Shares			Weighted-Average Exercise Price		Weighted-Average Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2016		3,148,006		$	8.93			$	10,437,947
Granted		1,332,400		$	11.95
Exercised		(291,439	)	$	5.28			$	2,689,563
Forfeited		(528,953	)	$	14.80			$	1,502,894
Expired/cancelled		—
Outstanding, December 31, 2017		3,660,014		$	9.47		8.00	$	21,932,858
Options exercisable, December 31, 2017		1,574,788		$	7.62		6.85	$	12,971,099
Expected to vest, December 31, 2017		2,085,226		$	10.88

The weighted-average grant date fair values of options granted in the years ended December 31, 2017, 2016, and 2015 were $8.47, $5.22, and $6.07 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2017, 2016, and 2015 were $2.7 million, $0.6 million, and $2.0 million, respectively. The fair value of options that vested during the years ended December 31, 2017, 2016, and 2015 were $5.6 million, $4.6 million, and $3.2 million, respectively. As of December 31, 2017, there was approximately $13.0 million of unrecognized compensation cost related to stock options under the Company’s 2014 Plan or made pursuant to the 2016 Inducement Award Program, which is expected to be recognized over a weighted average period of 2.72 years.

Restricted Stock

On December 23, 2013, the Company issued 450,224 shares of restricted stock to employees and 79,067 shares of restricted stock to non-employees at a grant date fair value of $7.42 per share. The aggregate grant date fair value for the shares of restricted stock issued on December 23, 2013 totaled approximately $3.9 million. The awards of restricted stock contained a performance condition wherein the vesting commencement day was contingent upon the Company’s consummation of a liquidity event, as defined, prior to the fifth anniversary of the date of grant. Certain of the awards of restricted stock had a requisite service period that was complete upon grant. The remainder of the awards of restricted stock had a requisite service period of four years whereby the award vested 25% on the one year anniversary of a specified vesting commencement date, then ratably on the first day of each calendar quarter for 12 quarters, subject to continuous service by the individual and achievement of the performance target. Due to the nature of the performance condition, the Company had concluded that the performance condition was not probable of achievement and therefore, recognition of compensation cost had been deferred until the occurrence of a liquidity event, as defined. The Company records stock-based compensation expense for restricted stock awards based on the grant date fair value for employees and the reporting date and upon vesting fair value for non-employees. The fair value of the award is considered the intrinsic value as of each measurement date. Compensation expense related to the restricted stock awards is being recognized over the associated requisite service period which commenced on March 25, 2014. The Company recorded approximately $0.2 million and $0.3 million of stock-based compensation expense related to restricted stock during 2017 and 2016, respectively, of which approximately $132,154 and $3,000 was as a result of mark to market adjustments related to non-employees.

The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Restricted shares as of December 31, 2016		92,972		$	8.08
Granted		—
Vested		(90,566	)	$	8.56
Forfeited		(2,406	)	$	7.42
Restricted shares as of December 31, 2017		-		$	-

As of December 31, 2017, there was approximately $0 of unrecognized compensation cost related to the restricted stock awards granted on December 23, 2013 with a performance condition. The recognition of the compensation cost for these awards did not begin until the closing of the initial public offering on March 25, 2014.

Restricted Stock Units

On February 21, 2017, as part of the Company’s annual grant of equity, the Company issued 423,650 RSUs to employees. In addition, the Company occasionally issues RSUs not in connection with the annual grant process to employees. 100% of each RSU grant vests on either the first or the third anniversary of the grant date, subject, in each case, to the individual’s continued service through the applicable vesting date. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted and recognized on a straight-line basis over the vesting period. The Company recorded approximately $2.0 million and $0.8 million of stock-based compensation expense related to the RSUs in 2017 and 2016, respectively.

A following table summarizes the Company’s RSU activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Unvested balance, December 31, 2016		431,688		$	7.96
Granted		449,900		$	10.34
Vested		(26,000	)	$	7.70
Forfeited		(126,850	)	$	8.96
Outstanding, December 31, 2017		728,738		$	9.26

As of December 31, 2017, there was approximately $4.0 million of unrecognized compensation cost related to RSUs, which is expected to be recognized over a weighted average period of 1.91 years.

Employee Stock Purchase Plan

The first offering period under the ESPP opened on January 2, 2015. The Company issued 44,789 shares issued during the year ended December 31, 2017. The Company recorded approximately $0.2 million and $0.1 million of stock-based compensation expense related to the ESPP during 2017 and 2016, respectively.

Compensation Expense Summary

The Company has recognized the following compensation cost related to share-based awards:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Research and development	$	6,496	$	2,136	$	2,079
General and administrative		5,784		3,689		2,635
Total	$	12,280	$	5,825	$	4,714

Compensation expense by type of award:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Stock options	$	6,512	$	4,674	$	3,660
Restricted stock		158		266		909
Restricted stock units		2,021		780		62
Employee stock purchase plan		176		105		83
Warrant		3,413		—		—
Total	$	12,280	$	5,825	$	4,714

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

9. Income Taxes

For the year ended December 31, 2017, the Company has taxable income primarily due to timing differences. The losses are fully offset with available NOLs for regular federal and state tax purposes. The Company does have a tax liability for Alternative Minimum Tax in 2017, however due to tax reform, the amount that will be paid this year is fully refundable through 2021 and thus the net result is that the Company recorded an income tax receivable rather than a tax expense for the year ended December 31, 2017. The Company recorded a receivable of approximately $1.0 million and a payable of approximately $1.0 million for the Alternative Minimum Tax which is included in other assets and accrued expenses, respectively, in the accompanying consolidated balance sheets as of December 31, 2017. The Company has recorded a full valuation allowance on its deferred tax assets and thus, for the year ended December 31, 2017 there is no deferred tax expense recorded. For the years ended December 31, 2016 and 2015, there was no current or deferred tax expense recorded due to the Company's net losses and increases in its deferred tax asset valuation allowance. The U.S. components of loss before income taxes and a reconciliation of the statutory federal income rate to with the provision for income taxes follow:

	Year ended December 31,
	2017			2016			2015
Federal tax at statutory rate		34.0	%		34.0	%		34.0	%
State and local tax at statutory rate		3.8			1.4			3.0
Research and development tax credits		11.9			6.4			0.4
Equity compensation		(0.6	)		(0.2	)		(0.6	)
Alternative minimum tax		(1.3	)		—			—
Change in valuation allowance		6.9			(41.6	)		(36.8	)
Impact of US tax reform		(54.7	)		—			—
Effective tax rate		0.0	%		0.0	%		0.0	%

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. When realization of the deferred tax asset is more likely than not to occur, the benefit related to the deductible temporary differences attributable to operations is recognized as a reduction of income tax expense. Valuation allowances are provided against deferred tax assets when, based on all available evidence, it is considered more likely than not that some portion or all of the recorded deferred tax assets will not be realized in future periods. The Company cannot be certain that future taxable income will be sufficient to realize its deferred tax assets, and accordingly a full valuation allowance has been provided on its deferred tax assets. The Company continues to maintain the underlying tax benefits to offset future taxable income and to monitor the need for a valuation allowance based on the profitability of its future operations. The valuation allowance decreased by approximately $4.9 million and increased by approximately $56.4 million, during the years ended December 31, 2017 and 2016. Significant components of the Company’s deferred tax assets and liabilities are as follows:

		December 31,
		2017			2016
	(in thousands)
Deferred tax assets:
Accrued expenses		$	4,305		$	2,170
Deferred revenue			32,093			12,157
Intangible assets			509			449
Restricted stock			—			45
Non-qualified stock options			3,129			2,963
Research and development credits			25,322			10,510
Net operating loss carryforward			42,335			84,372
Other			600			326
Total deferred tax assets			108,293			112,992
Less valuation allowance			(108,112	)		(112,986	)
Total deferred tax assets, net of valuation allowance			181			6
Deferred tax liabilities:
Fixed assets			(181	)		(6	)
Total deferred tax liabilities			(181	)		(6	)
Net deferred tax asset		$	—		$	—

At December 31, 2017 and December 31, 2016, the Company has approximately $0.8 million (after amortization of $1.1 million) and $0.9 million (after amortization of $1.0 million), respectively, of start-up expenses capitalized for income tax purposes with amortization available to offset future federal, state and local income tax. At December 31, 2017 and 2016, the Company has approximately $179.7 million and $234.5 million, respectively, of federal net operating loss (NOL) carry-forwards which expire through 2036. Additionally, at December 31, 2017 and 2016, the Company has approximately $74.6 million and $103.9 million, respectively, of state net operating loss (NOL) carry-forwards which expire through 2036. As a result of the adoption of ASU 2016-09 for the year ended December 31, 2017, the benefits of tax deductions related to equity compensation in excess of book compensation expense that were previously suspended are now recognized for financial statement purposes. To record this tax benefit, both the NOL deferred tax asset and valuation allowance increased by $1.3 million, with a net zero tax impact recorded directly to retained earnings. For comparison purposes, the 2016 NOL deferred tax asset above (prior to the adoption of ASU 2016-09) does not include the benefit of these tax deductions. The Company also has approximately $25.7 million of federal and state research and development tax credit carry-forwards. The NOL and research and development tax credit carry-forwards which expire through 2037, will be utilized for tax purposes at such time the Company generates taxable income. The NOL and research and development tax credit carry-forwards may be limited in certain circumstances, including ownership changes.

Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carry-forwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception, two of which resulted in a change in control and limitations on the deductibility of existing NOLs at the dates of change of control. As of December 31, 2016, there were $170.0 million unlimited NOLs available to offset taxable income in future years, which allowed for the complete offset of taxable income for the year ended December 31, 2017.

For applicable years, the Company generated research credits but has not conducted a study to document its qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carry-forwards and the valuation allowance.

The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2017, 2016 and 2015, the Company had no accrued uncertain tax positions or associated interest or penalties and no amounts have been recognized in the Company’s consolidated statements of operations.

The Company files income tax returns in the U.S. federal jurisdiction, and various state jurisdictions. Generally, the Company’s 2014 through 2016 tax years remain open and subject to examination by federal and state taxing authorities. However, federal and state net operating losses from 2009 through 2016 are subject to review by taxing authorities in the year utilized.

The Tax Cuts and Jobs Act (the Act), which was signed on December 22, 2017, makes significant change in U.S. tax law including a reduction in the corporate tax rates to 21% starting in 2018. The legislation reduced the U.S. corporate tax rate from the current rate of 35% to 21%for tax years beginning after December 31, 2017. As a result of the enacted law, the Company was required to revalue deferred tax assets and liabilities existing as of December 31, 2017 from the 35% federal rate in effect through the end of 2017, to the new 21% rate. As a result of the change in law, the Company recorded a $43.0 million reduction in the deferred tax asset and corresponding valuation allowance.

In accordance with SAB 118, we have determined that our deferred tax asset value and associated valuation allowance reduction is a provisional amount and a reasonable estimate at December 31, 2017. The final impact may differ from this provisional amount due to, among other things, changes in interpretations and assumptions we have made thus far and the issuance of additional regulatory or other guidance. We expect to complete the final impact within the measurement period.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

10. Commitments and Contingencies

The Company leases approximately 45,362 square feet of office and lab space in Cambridge, Massachusetts under a lease which was most recently amended in July 2016, collectively, the Lease. Total monthly lease payments under the initial base rent was approximately $242,000 and is subject to annual rent escalations. In addition to such annual rent escalations, base rent payments for a portion of said premises commenced on January 1, 2017 in the monthly amount of approximately $22,000. Landlord contributions included in the Lease from the landlord totaled $2,169,920, including $70,526 in leasehold improvements not yet utilized. The landlord contributions are being accounted for as a deferred lease incentive and reduction in monthly rent expense over the term of the Lease. The term of the Lease with respect to the office space expires on September 11, 2026, with one five year extension option available. The term of the Lease with respect to the lab space expires on November 30, 2021, with an extension option for one additional period of two years. The total security deposit in connection with the Lease of $1,280,857 is in the form of a letter of credit and is included in other assets in the Company’s consolidated balance sheets as of December 31, 2017 and December 31, 2016.

The Company recognizes rent expense for the space which it currently occupies and records a deferred lease obligation representing the cumulative difference between actual facility lease payments and lease expense recognized ratably over the lease period, which is included in the Company’s consolidated balance sheets as of December 31, 2017 and December 31, 2016.

Under the Lease, the Company took possession of the remaining 3,384 square feet of office space on January 1, 2017, and subleased this space commencing on that date (the Sublease) as it did not intend to use the space for its operations. The term of the Sublease is two years and the monthly rent to be received by the Company is approximately $22,000. Under the Sublease, the Company’s operating lease obligations through 2018 are partially offset by future Sublease payments to it of approximately $0.3 million. The total security deposit in connection with the Sublease of $21,432 is included in other current assets and other liabilities in the Company’s consolidated balance sheets as of December 31, 2017 and December 31, 2016.

At December 31, 2017, the Company’s future minimum payments required under these leases are as follows:

			Lease Payments
	Operating		to be Received		Net Operating
	Lease		from Sublease		Lease Payments
	(in thousands)
2018	$	3,579	$	257	$	3,322
2019		3,626		—	$	3,626
2020		3,675		—	$	3,675
2021		3,684		—	$	3,684
2022		3,307		—	$	3,307
Thereafter		12,573		—	$	12,573
Total	$	30,444	$	257	$	30,187

The Company recorded approximately $3.2 million and $2.5 million in rent expense for the years ended December 31, 2017 and 2016, respectively.

Under the Company’s agreement with IQVIA, formerly known as Quintiles IMS, to provide CRO services for the PRO₂TECT and INNO₂VATE programs, the total remaining contract costs as of December 31, 2017 were approximately $276.4 million. The estimated period of performance for the committed work with IQVIA is through the first quarter of 2020. The Company contracts with various other organizations to conduct research and development activities with remaining contract costs to the Company of approximately $52.4 million at December 31, 2017. The scope of the services under these research and development contracts can be modified and the contracts cancelled by the Company upon written notice. In some instances, the contracts may be cancelled by the third party upon written notice.

The Company filed an opposition in Europe against FibroGen, Inc.’s, or FibroGen’s, European Patent No. 1463823, or the ’823 EP Patent, and an oral proceeding took place March 8 and 9, 2016. Following the oral proceeding, the European Opposition Division ruled that the patent as granted did not meet the requirements for patentability under the European Patent Convention and, therefore, revoked the patent in its entirety. FibroGen has appealed that decision and the appeal process is expected to take two to three years. Likewise, with regard to the invalidity proceeding that we filed in Japan against certain claims of FibroGen’s Japanese Patent No. 4804131, or the ’131 JP Patent, which is the Japanese counterpart to the ’823 EP Patent, the Japan Patent Office, or JPO, issued a preliminary decision finding all of the challenged claims to be invalid. FibroGen subsequently amended the claims and the JPO accepted the amendments. The resulting’131 JP Patent does not cover vadadustat or any pyridine carboxamide compounds. To date, FibroGen has been unsuccessful in its attempts to obtain a patent in the United States covering the same claim scope as it obtained initially in Europe and Japan in the ’823 EP Patent and ’131 JP Patents. In the event FibroGen were to obtain such a patent in the United States, the Company may decide to challenge the patent as we have done in Europe and Japan.

On May 13, 2015, May 20, 2015 and July 6, 2015, the Company filed oppositions to FibroGen’s European Patent Nos. 2322155, or the ’155 EP Patent, 1633333, or the ’333 EP patent, and 2322153, or the ’153 EP Patent requesting the patents be revoked in their entirety. These related patents claim, among other things, various compounds that either stabilize HIFα or inhibit a HIF hydroxylase or a HIF prolyl hydroxylase for treating or preventing various conditions, including, inter alia, iron deficiency, microcytosis associated with iron deficiency, anemia of chronic disease, anemia wherein the subject has a transferrin saturation of less than 20%, anemia refractory to treatment with exogenously administered erythropoietin, or EPO, and microcytosis in microcytic anemia. Such method of use patents do not prevent persons from using the compound for other uses, including any previously known use of the compound. In particular, these patents do not claim methods of using any of our product candidates for purposes of inhibiting hypoxia-inducible factor prolyl hydroxylases, or HIF-PHs, for the treatment of anemia secondary to CKD. While the Company does not believe these patents will prevent us from commercializing vadadustat for the treatment of anemia secondary to CKD, the Company filed these oppositions to provide us and our collaborators with maximum flexibility for developing vadadustat and the Company’s pipeline of HIF-PHIs.

Oppositions to the ’155 EP Patent and the ’153 EP Patent were also filed by Glaxo Group Limited, or Glaxo, and by Bayer Intellectual Property GmbH, Bayer Pharma Aktiengesellschaft, and Bayer Animal Health GmbH, or collectively Bayer.

With regards to the opposition that we filed in Europe against the ’333 EP patent, an oral proceeding took place on December 8 and 9, 2016. Following the oral proceeding, the European Opposition Division ruled that the patent as granted did not meet the requirements for patentability under the European Patent Convention and, therefore, revoked the patent in its entirety. On December 9, 2016, FibroGen filed a notice to appeal the decision to revoke the ’333 EP Patent.

In oral proceedings held on May 29, 2017 regarding the ‘155 EP Patent, the European Opposition Division ruled that the '155 EP Patent as granted did not meet the requirements for patentability under the European Patent Convention and, therefore, revoked the patent in its entirety. FibroGen filed a notice to appeal the decision to revoke the ’155 EP Patent on May 29, 2017.

Subsequently, in related oral proceedings held on May 31, 2017 and June 1, 2017 for the '153 EP Patent, the European Opposition Division maintained the patent after FibroGen significantly narrowed the claims to an indication for which vadadustat is not intended to be developed. We and Glaxo separately filed notices to appeal the decision to maintain the ’153 EP Patent on November 9, 2017. Bayer filed a notice to appeal the decision on November 14, 2017.

The Company’s policy is to record a liability if a loss in a significant legal dispute is considered probable and an amount can be reasonably estimated. The Company provides disclosure when a loss in excess of any reserve is reasonably possible, and the Company is in a position to estimate the potential loss or range of possible loss. Significant judgment is required to assess the likelihood of various potential outcomes and the quantification of loss in those scenarios. The Company’s estimates change as litigation progresses and new information comes to light. Changes in Company estimates could have a material impact on the Company’s results and financial position.

Net Loss per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss per Share

12. Net Loss per Share

The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect:

	Year ended December 31,
	2017		2016		2015
Warrants		509,611		—		—
Outstanding stock options		3,660,014		3,148,006		2,206,635
Unvested restricted stock		—		92,972		216,716
Unvested restricted stock units		728,738		431,688		24,425
Total		4,898,363		3,672,666		2,447,776

Quarterly Results (unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Results (unaudited)

13. Quarterly Results (unaudited)

	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2017			2017			2017			2017
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	20,865		$	28,520		$	41,283		$	87,316
Operating expenses	$	65,837		$	50,656		$	65,459		$	75,949
Loss from operations	$	(44,972	)	$	(22,136	)	$	(24,176	)	$	11,367
Other income, net	$	429		$	618		$	1,042		$	914
Net (loss)/income	$	(44,543	)	$	(21,518	)	$	(23,134	)	$	12,281
Net (loss)/income per share:
basic	$	(1.15	)	$	(0.53	)	$	(0.49	)	$	0.26
diluted	$	(1.15	)	$	(0.53	)	$	(0.49	)	$	0.25
Weighted-average number of common shares:
basic		38,759,221			40,819,957			46,938,618			47,353,166
diluted		38,759,221			40,819,957			46,938,618			49,719,548


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2016			2016			2016			2016
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	—		$	—		$	—		$	1,535
Operating expenses	$	26,046		$	36,188		$	36,182		$	39,579
Loss from operations	$	(26,046	)	$	(36,188	)	$	(36,182	)	$	(38,044	)
Other income (expense), net	$	248		$	409		$	(126	)	$	182
Net loss	$	(25,798	)	$	(35,779	)	$	(36,308	)	$	(37,862	)
Net loss per share —basic and diluted	$	(0.70	)	$	(0.95	)	$	(0.96	)	$	(0.99	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation

New Accounting Pronouncements

New Accounting Pronouncements – Recently Adopted

•

Upon adoption in January 2017, no other aspects of ASU 2016-09 had a material effect on the Company's unaudited condensed consolidated financial statements or related footnote disclosures.

New Accounting Pronouncements – Not Yet Adopted

Segment Information

Derivative Financial Instruments

Use of Estimates

Cash and Cash Equivalents

Investments

Accounts Receivable

Revenue Recognition

Multiple-Element Arrangements

•

Persuasive evidence of an arrangement exists;

•

Delivery has occurred or services have been rendered;

•

The seller’s price to the buyer is fixed or determinable; and

•

Collectability is reasonably assured.

Collaborative Arrangements

Patents

Costs incurred in connection with the application for and issuance of patents are expensed as incurred.

Research and Development Costs

Research and development costs are expensed as incurred.

Income Taxes

Stock-Based Compensation

The Company adopted ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, effective in the first quarter of the year ended December 31, 2017. Prior to adoption, share-based compensation expense was recognized on a straight-line basis, net of estimated forfeitures, such that expense was recognized only for share-based awards that are expected to vest. A forfeiture rate was estimated annually and revised, if necessary, in subsequent periods if actual forfeitures differed from initial estimates. Upon adoption, the Company no longer applies a forfeiture rate and instead will account for forfeitures as they occur.

Fair Value of Financial Instruments

•

Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date.

•

Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active, or for which all significant inputs are observable, either directly or indirectly.

•

Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Net Loss per Share

Property and Equipment

The following is the summary of property and equipment and related accumulated depreciation as of December 31, 2017 and 2016.

	Useful Life	December 31, 2017			December 31, 2016
		(in thousands)
Computer equipment and software	3	$	630		$	476
Furniture and fixtures	5		800			729
Equipment	7		628			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		2,582			1,763
Office equipment under capital lease	3		36			36
			4,676			3,054
Less accumulated depreciation			(1,059	)		(442	)
Net property and equipment		$	3,617		$	2,612

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Property and Equipment and Related Accumulated Depreciation

The following is the summary of property and equipment and related accumulated depreciation as of December 31, 2017 and 2016.

	Useful Life	December 31, 2017			December 31, 2016
		(in thousands)
Computer equipment and software	3	$	630		$	476
Furniture and fixtures	5		800			729
Equipment	7		628			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		2,582			1,763
Office equipment under capital lease	3		36			36
			4,676			3,054
Less accumulated depreciation			(1,059	)		(442	)
Net property and equipment		$	3,617		$	2,612

Available for Sale Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Summary of Available for Sale Securities at Fair Value

Available for sale securities at December 31, 2017 and 2016 consist of the following:

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2017
Cash and cash equivalents	$	70,156	$	—	$	—		$	70,156
Available for sale securities:
Certificates of deposit	$	14,117	—		—			$	14,117
U.S. government debt securities		175,155	—			(352	)		174,803
Corporate debt securities		58,806	—			(90	)		58,716
Total available for sale securities	$	248,078	$	—	$	(442	)	$	247,636
Total cash, cash equivalents, and available for sale securities	$	318,234	$	—	$	(442	)	$	317,792

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2016
Cash and cash equivalents	$	187,335	$	—	$	—		$	187,335
Available for sale securities:
Certificates of deposit	$	12,698	—			—		$	12,698
U.S. government debt securities		50,952	—			(32	)		50,920
Corporate debt securities		9,398	—			(8	)		9,390
Total available for sale securities	$	73,048	$	—	$	(40	)	$	73,008
Total cash, cash equivalents, and available for sale securities	$	260,383	$	—	$	(40	)	$	260,343

Estimated Fair Value of Available for Sale Securities at Fair Value by Contractual Maturity

The estimated fair value of the Company’s available for sale securities balance at December 31, 2017, by contractual maturity, is as follows:

Due in one year or less	$	217,884
Due after one year		29,752
Total available for sale securities	$	247,636

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Assets Measured or Disclosed at Fair Value on Recurring Basis

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2017 and December 31, 2016 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2017
Assets:
Cash and cash equivalents	$	70,156	$	—	$	—	$	70,156
Certificates of deposit		—		14,117		—		14,117
U.S. government debt securities		—		174,803		—		174,803
Corporate debt securities		—		58,716		—		58,716
	$	70,156	$	247,636	$	—	$	317,792

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2016
Assets:
Cash and cash equivalents	$	187,335	$	—	$	—	$	187,335
Certificates of deposit		—		12,698		—		12,698
U.S. government debt securities		—		50,920		—		50,920
Corporate debt securities		—		9,390		—		9,390
	$	187,335	$	73,008	$	—	$	260,343

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Components of Accrued Expenses

Accrued expenses are as follows:

	December 31, 2017		December 31, 2016
	(in thousands)
Accrued clinical	$	43,297	$	23,643
Accrued bonus		3,388		2,995
Income tax payable		987		—
Professional fees		808		539
Accrued vacation		797		513
Accrued payroll		795		596
Accrued severance		—		29
Other		2,369		1,946
Total accrued expenses	$	52,441	$	30,261

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Reserved Shares of Common Stock for Future Issuance

The Company has reserved for future issuance the following number of shares of common stock:

	December 31, 2017		December 31, 2016
Common stock options and RSU's outstanding ⁽¹⁾		4,388,752		3,579,694
Shares available for issuance under the 2014 Plan ⁽²⁾		1,790,600		1,140,328
Warrant to purchase common stock		509,611		—
Shares available for issuance under the ESPP ⁽³⁾		652,290		803,105
Total		7,341,253		5,523,127

⁽¹⁾

Includes awards granted under the 2014 Plan and the 2016 Inducement Award Program.

⁽²⁾

⁽³⁾

On February 28, 2017 and February 28, 2016, the shares reserved for future issuance under the ESPP increased by 0 and 273,404 shares, respectively, pursuant to the ESPP Evergreen Provision.

Schedule of Assumptions Used in Black-Scholes Option Pricing Model

The assumptions used in the Black-Scholes pricing model to estimate the grant date fair value of options granted to employees are as follows:

	Year ended December 31,
	2017	2016		2015
Risk-free interest rate	1.81% - 2.27%	1.16% - 2.03%		1.44% - 1.95%
Dividend yield	0.00%		0.00%		0.00%
Volatility	78.57% - 85.81%	64.78% - 82.40%		62.47% - 81.25%
Expected term (years)	5.51 - 6.25	5.51 - 6.25		5.51 - 6.25

Schedule of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2017:

	Shares			Weighted-Average Exercise Price		Weighted-Average Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2016		3,148,006		$	8.93			$	10,437,947
Granted		1,332,400		$	11.95
Exercised		(291,439	)	$	5.28			$	2,689,563
Forfeited		(528,953	)	$	14.80			$	1,502,894
Expired/cancelled		—
Outstanding, December 31, 2017		3,660,014		$	9.47		8.00	$	21,932,858
Options exercisable, December 31, 2017		1,574,788		$	7.62		6.85	$	12,971,099
Expected to vest, December 31, 2017		2,085,226		$	10.88

Schedule of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Restricted shares as of December 31, 2016		92,972		$	8.08
Granted		—
Vested		(90,566	)	$	8.56
Forfeited		(2,406	)	$	7.42
Restricted shares as of December 31, 2017		-		$	-

Compensation Cost Related to Share-Based Awards

The Company has recognized the following compensation cost related to share-based awards:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Research and development	$	6,496	$	2,136	$	2,079
General and administrative		5,784		3,689		2,635
Total	$	12,280	$	5,825	$	4,714

Schedule of Compensation Expense by Type of Award

Compensation expense by type of award:

	Years ended December 31,
	2017		2016		2015
	(in thousands)
Stock options	$	6,512	$	4,674	$	3,660
Restricted stock		158		266		909
Restricted stock units		2,021		780		62
Employee stock purchase plan		176		105		83
Warrant		3,413		—		—
Total	$	12,280	$	5,825	$	4,714

Restricted Stock Units

Schedule of Restricted Stock Activity

A following table summarizes the Company’s RSU activity for the year ended December 31, 2017:

	Shares			Weighted-Average Grant Date Fair Value
Unvested balance, December 31, 2016		431,688		$	7.96
Granted		449,900		$	10.34
Vested		(26,000	)	$	7.70
Forfeited		(126,850	)	$	8.96
Outstanding, December 31, 2017		728,738		$	9.26

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Components of Loss Before Income Taxes and Reconciliation of Statutory Federal Income Tax Rate to Provision for Income Taxes

The U.S. components of loss before income taxes and a reconciliation of the statutory federal income rate to with the provision for income taxes follow:

	Year ended December 31,
	2017			2016			2015
Federal tax at statutory rate		34.0	%		34.0	%		34.0	%
State and local tax at statutory rate		3.8			1.4			3.0
Research and development tax credits		11.9			6.4			0.4
Equity compensation		(0.6	)		(0.2	)		(0.6	)
Alternative minimum tax		(1.3	)		—			—
Change in valuation allowance		6.9			(41.6	)		(36.8	)
Impact of US tax reform		(54.7	)		—			—
Effective tax rate		0.0	%		0.0	%		0.0	%

Schedule of Significant Deferred Tax Assets and Liabilities

Significant components of the Company’s deferred tax assets and liabilities are as follows:

		December 31,
		2017			2016
	(in thousands)
Deferred tax assets:
Accrued expenses		$	4,305		$	2,170
Deferred revenue			32,093			12,157
Intangible assets			509			449
Restricted stock			—			45
Non-qualified stock options			3,129			2,963
Research and development credits			25,322			10,510
Net operating loss carryforward			42,335			84,372
Other			600			326
Total deferred tax assets			108,293			112,992
Less valuation allowance			(108,112	)		(112,986	)
Total deferred tax assets, net of valuation allowance			181			6
Deferred tax liabilities:
Fixed assets			(181	)		(6	)
Total deferred tax liabilities			(181	)		(6	)
Net deferred tax asset		$	—		$	—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Required Under Leases

At December 31, 2017, the Company’s future minimum payments required under these leases are as follows:

			Lease Payments
	Operating		to be Received		Net Operating
	Lease		from Sublease		Lease Payments
	(in thousands)
2018	$	3,579	$	257	$	3,322
2019		3,626		—	$	3,626
2020		3,675		—	$	3,675
2021		3,684		—	$	3,684
2022		3,307		—	$	3,307
Thereafter		12,573		—	$	12,573
Total	$	30,444	$	257	$	30,187

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share

The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect:

	Year ended December 31,
	2017		2016		2015
Warrants		509,611		—		—
Outstanding stock options		3,660,014		3,148,006		2,206,635
Unvested restricted stock		—		92,972		216,716
Unvested restricted stock units		728,738		431,688		24,425
Total		4,898,363		3,672,666		2,447,776

Quarterly Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Results

	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2017			2017			2017			2017
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	20,865		$	28,520		$	41,283		$	87,316
Operating expenses	$	65,837		$	50,656		$	65,459		$	75,949
Loss from operations	$	(44,972	)	$	(22,136	)	$	(24,176	)	$	11,367
Other income, net	$	429		$	618		$	1,042		$	914
Net (loss)/income	$	(44,543	)	$	(21,518	)	$	(23,134	)	$	12,281
Net (loss)/income per share:
basic	$	(1.15	)	$	(0.53	)	$	(0.49	)	$	0.26
diluted	$	(1.15	)	$	(0.53	)	$	(0.49	)	$	0.25
Weighted-average number of common shares:
basic		38,759,221			40,819,957			46,938,618			47,353,166
diluted		38,759,221			40,819,957			46,938,618			49,719,548


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2016			2016			2016			2016
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	—		$	—		$	—		$	1,535
Operating expenses	$	26,046		$	36,188		$	36,182		$	39,579
Loss from operations	$	(26,046	)	$	(36,188	)	$	(36,182	)	$	(38,044	)
Other income (expense), net	$	248		$	409		$	(126	)	$	182
Net loss	$	(25,798	)	$	(35,779	)	$	(36,308	)	$	(37,862	)
Net loss per share —basic and diluted	$	(0.70	)	$	(0.95	)	$	(0.96	)	$	(0.99	)

Nature of Organization and Operations - Additional Information (Details)	1 Months Ended				12 Months Ended
	Apr. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) Patient shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Nature Of Organization And Operations [Line Items]
Proceeds from sale of stock					$ 373,100,000
Proceeds from issuance of public offering					114,580,000	$ 66,623,000	$ 82,750,000
Cash and cash equivalents and available for sale securities			$ 260,343,000		$ 317,792,000	$ 260,343,000
Number of months for operating plan sufficiently funded by cash resources					12 months
Otsuka Pharmaceutical Co. Ltd. and Mitsubishi Tanabe Pharma Corporation
Nature Of Organization And Operations [Line Items]
Minimum committed amount in cost share funding and license payments under collaboration agreements					$ 573,000,000
Amount received from cost-share funding and license payments					$ 272,000,000
Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares \| shares					8,672,270	7,865,293	10,083,070
Common Stock \| Vifor Pharma
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares \| shares					3,571,429
Follow-on public offering
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of public offering					$ 292,600,000
Follow-on public offering \| Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of public offering					$ 30,500,000
Pro Two Tech And Inno Two Vate
Nature Of Organization And Operations [Line Items]
Number of patients \| Patient					6,900
License Agreement \| Vifor Pharma
Nature Of Organization And Operations [Line Items]
Proceeds from sale of stock					$ 50,000,000
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation
Nature Of Organization And Operations [Line Items]
Collaborative arrangement right description					In December 2015, the Company entered into a collaboration agreement with MTPC to develop and commercialize vadadustat in Japan and certain other countries in Asia, collectively, the MTPC Territory, for total payments of up to $245.0 million, comprised of a $20.0 million upfront payment, up to $50.0 million in specified development and regulatory milestones, and up to $175.0 million in specified commercial milestones, as well as tiered double-digit royalty payments up to 20% on sales of vadadustat in the MTPC Territory (Note 3).
Upfront cash payment received					$ 0	$ 40,000,000
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation \| Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue				$ 245,000,000	265,000,000
Additional milestone payments development costs fund				$ 50,000,000
Royalty payment percentage				20.00%			20.00%
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation \| Upfront
Nature Of Organization And Operations [Line Items]
Upfront cash payment received				$ 20,000,000	20,000,000
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation \| Commercial Milestone Payments
Nature Of Organization And Operations [Line Items]
Milestone revenue				$ 175,000,000
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation \| Commercial Milestone Payments \| Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue					$ 175,000,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company. Ltd. \| Global Development Plan
Nature Of Organization And Operations [Line Items]
Reimbursement for Otsuka's share of costs previously incurred	$ 200,000	$ 33,800,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company. Ltd. \| Minimum \| Global Development Plan
Nature Of Organization And Operations [Line Items]
Collaborative arrangements cost sharing payments	163,600,000		153,600,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company. Ltd. \| Upfront
Nature Of Organization And Operations [Line Items]
Upfront cash payment received	73,000,000		125,000,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company. Ltd. \| Commercial Milestone Payments \| Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue	525,000,000		575,000,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company. Ltd. \| Potential Development and Commercialization Milestones \| Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue	$ 132,000,000		$ 190,000,000

Summary of Significant Accounting Policies - Additional Information (Details)		3 Months Ended					12 Months Ended
	Jan. 02, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Net operating loss deferred tax asset		$ 42,335,000				$ 84,372,000	$ 42,335,000	$ 84,372,000
Collaboration revenue		87,316,000	$ 41,283,000	$ 28,520,000	$ 20,865,000	1,535,000	$ 177,984,000	1,535,000
Number of operating segments \| Segment							1
Write-offs of bad debt							$ 0	0
Allowance for doubtful accounts		0				0	0	0
Significant uncertain tax positions		0				$ 0	$ 0	0
Expected dividend yield							0.00%
Depreciation expense							$ 616,000	295,000	$ 96,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life							3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life							7 years
Otsuka U.S. Agreement
Summary Of Significant Accounting Policies [Line Items]
Cost share costs for license agreement							$ 700,000
Reimbursable by Otsuka							200,000
ASU 2016-09
Summary Of Significant Accounting Policies [Line Items]
Net operating loss deferred tax asset		400,000					400,000
Offsetting valuation allowance		$ 400,000					400,000
Cumulative-effect adjustment to reduce retained earnings	$ 200,000
ASC 606
Summary Of Significant Accounting Policies [Line Items]
Increase in current assets							3,200,000	0
Changes in current liabilities							0	0
ASC 606 \| Collaboration Agreements \| Otsuka Pharmaceutical Company. Ltd.
Summary Of Significant Accounting Policies [Line Items]
Collaboration revenue							0	0
ASC 606 \| Collaboration Agreements \| Mitsubishi Tanabe Pharma Corporation
Summary Of Significant Accounting Policies [Line Items]
Increase in revenue							$ 3,200,000	$ 0

Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 4,676	$ 3,054
Less accumulated depreciation	(1,059)	(442)
Net property and equipment	$ 3,617	2,612
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 630	476
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	$ 800	729
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	$ 628	50
Leasehold improvements
Property, Plant and Equipment [Line Items]
Leasehold improvements, Useful Life	Shorter of the useful life or remaining lease term (10 years)
Gross property, plant and equipment	$ 2,582	1,763
Leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	10 years
Office equipment under capital lease
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 36	$ 36

Strategic Collaborations and Other Significant Agreements - Additional Information (Details)					1 Months Ended					3 Months Ended					12 Months Ended
	May 12, 2017 USD ($)	Apr. 25, 2017 USD ($)	Feb. 09, 2017 USD ($) $ / shares shares	Jan. 02, 2017 USD ($)	Jan. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	May 31, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) AccountingUnit $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognized revenue under license agreement										$ 87,316,000	$ 41,283,000	$ 28,520,000	$ 20,865,000	$ 1,535,000	$ 177,984,000	$ 1,535,000
Deferred revenue, current						$ 84,910,000				84,910,000				81,968,000	84,910,000	81,968,000
Allocated arrangement consideration															236,800,000
Deferred revenue, noncurrent						$ 97,957,000				$ 97,957,000				$ 115,321,000	$ 97,957,000	$ 115,321,000
Common stock shares sold \| shares						47,612,619				47,612,619				38,615,709	47,612,619	38,615,709
Common stock, par value \| $ / shares						$ 0.00001				$ 0.00001				$ 0.00001	$ 0.00001	$ 0.00001
Proceeds from common stock sold															$ 373,100,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received															0	$ 40,000,000
Development costs incurred															19,000,000
Expected additional development costs															2,400,000
Expected reimbursement for development costs															$ 1,400,000
Collaboration Agreement, expiration period															10 years
Collaboration Agreement, notice period for termination															12 months
Number of accounting units \| AccountingUnit															2
Estimated cost															$ 21,400,000
Non-substantive development milestone received															6,000,000
Recognized revenue under license agreement															39,700,000
Deferred revenue, current						$ 7,500,000				$ 7,500,000					7,500,000
Accounts receivable						1,300,000				1,300,000					1,300,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue									$ 245,000,000						265,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received									20,000,000						20,000,000
Incurred clinical and commercial development cost															20,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development and Regulatory Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															50,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Commercial Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue									$ 175,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Commercial Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															$ 175,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development, Regulatory and Sales Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalty payments on sales															20.00%
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development, Regulatory and Commercial Events
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															$ 225,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue						6,000,000									10,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development Milestones \| Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue					$ 4,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Development Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															10,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Regulatory Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received															40,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Approval Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received															40,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Sales Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															175,000,000
Mitsubishi Tanabe Pharma Corporation \| New Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Data access fee receivable											$ 25,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															$ 0
Number of accounting units \| AccountingUnit															3
Recognized revenue under license agreement															$ 86,000,000	1,500,000
Deferred revenue, current						45,300,000				45,300,000					45,300,000
Accounts receivable						17,300,000				17,300,000					$ 17,300,000
Percentage of market penetration for license agreement															90.00%
License agreement, notice period for termination															12 months
Cost share payment received																33,800,000
Estimated cost share payment receivable															$ 153,600,000
Allocated arrangement consideration															312,400,000
Deferred revenue						99,900,000				99,900,000					99,900,000
Deferred revenue, noncurrent						54,600,000				54,600,000					54,600,000
Unbilled accounts receivables						2,000,000				2,000,000					2,000,000
Cost share costs incurred															700,000
Reimbursable by Otsuka															200,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Global Development Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement for Otsuka's share of costs previously incurred								$ 33,800,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Minimum \| Global Development Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangements cost sharing payments				$ 153,600,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received																$ 125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Commercial Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															575,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Development Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received															125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Regulatory Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue															65,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize United States Collaboration and License Agreement \| Up-front, Non-refundable and Non-creditable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received															125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognized revenue under license agreement															52,300,000
Deferred revenue, current						32,100,000				32,100,000					32,100,000
Accounts receivable						15,600,000				15,600,000					15,600,000
Deferred revenue						70,800,000				70,800,000					70,800,000
Deferred revenue, noncurrent						38,700,000				38,700,000					38,700,000
Unbilled accounts receivables						$ 1,700,000				$ 1,700,000					$ 1,700,000
Milestone or royalty payments received		$ 0
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Global Development Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement for Otsuka's share of costs previously incurred													200,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Minimum \| Global Development Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimate Subsequent Cost Share Payment Receivable		163,600,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Commercial Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue		525,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Development Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue		80,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Regulatory Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue		52,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize International Collaboration and License Agreement \| Up-front, Non-refundable and Non-creditable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront cash payment received		$ 73,000,000
Janssen Pharmaceutica NV \| Development and Commercialize Research and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration Agreement, expiration period			10 years
Collaboration Agreement, notice period for termination			180 days
Upfront payment made in cash			$ 1,000,000
Warrant to purchase common stock, shares \| shares			509,611
Aggregate specified development milestone payments payable			$ 16,500,000
Specified commercial milestones as well as tiered, escalating royalties payable			$ 215,000,000
Johnson & Johnson Innovation \| Development and Commercialize Research and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Warrant to purchase common stock, shares \| shares			509,611
Fair value of warrant								$ 3,400,000					$ 3,400,000
Exercise price \| $ / shares			$ 9.81
Vifor (International) Ltd. \| License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue	$ 20,000,000
License agreement, notice period for termination	12 months
Deferred revenue, noncurrent							$ 4,700,000
Common stock shares sold \| shares							3,571,429
Common stock, par value \| $ / shares							$ 0.00001
Sale of stock, price per share \| $ / shares							$ 14.00
Proceeds from common stock sold							$ 50,000,000
Premium over the closing stock price of common stock \| $ / shares							$ 12.69
Premium amount over the closing stock price of common stock							$ 4,700,000

Available for Sale Securities - Summary of Available for Sale Securities at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 248,078	$ 73,048
Gross Unrealized Losses	(442)	(40)
Fair Value	247,636	73,008
Cash and cash equivalents	70,156	187,335	$ 49,778	$ 32,780
Cash and cash equivalents, Fair Value	70,156	187,335
Total cash, cash equivalents, and available for sale securities - Amortized Cost	318,234	260,383
Total cash, cash equivalents, and available for sale securities - Fair Value	317,792	260,343
U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	175,155	50,952
Gross Unrealized Losses	(352)	(32)
Fair Value	174,803	50,920
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	14,117	12,698
Fair Value	14,117	12,698
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	58,806	9,398
Gross Unrealized Losses	(90)	(8)
Fair Value	$ 58,716	$ 9,390

Available for Sale Securities - Estimated Fair Value of Available for Sale Securities by Contractual Maturity (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 217,884
Due after one year	29,752
Total available for sale securities	$ 247,636

Available for Sale Securities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) Security	Dec. 31, 2016 USD ($) Security
Investments Debt And Equity Securities [Abstract]
Gains (losses) on available for sale securities	$ 0	$ 0
Available-for-sale securities, unrealized loss position for more than12 months	9,000	$ 0
Available-for-sale securities, unrealized loss position fair value for more than12 months	$ 4,000,000
Available-for-sale, securities in unrealized loss positions,number of securities \| Security	57	27
Available-for-sale securities, unrealized loss position for less than12 months	$ 433,000	$ 40,000
Available-for-sale securities, unrealized loss position fair value for less than12 months	$ 229,500,000	$ 60,300,000

Fair Value of Financial Instruments - Assets Measured or Disclosed at Fair Value on Recurring Basis (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 0	$ 0
Fair value measurements recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	317,792,000	260,343,000
Fair value measurements recurring \| U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	174,803,000	50,920,000
Fair value measurements recurring \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	70,156,000	187,335,000
Fair value measurements recurring \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	247,636,000	73,008,000
Fair value measurements recurring \| Level 2 \| U.S. government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	174,803,000	50,920,000
Fair value measurements recurring \| Cash and cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	70,156,000	187,335,000
Fair value measurements recurring \| Cash and cash equivalents \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	70,156,000	187,335,000
Fair value measurements recurring \| Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	14,117,000	12,698,000
Fair value measurements recurring \| Certificates of deposit \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	14,117,000	12,698,000
Fair value measurements recurring \| Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	58,716,000	9,390,000
Fair value measurements recurring \| Corporate debt securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 58,716,000	$ 9,390,000

Fair Value of Financial Instruments - Additional Information (Details) - Level 3 - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 0	$ 0
Liabilities measured at fair value on recurring basis	$ 0	$ 0

Accrued Expenses - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued clinical	$ 43,297	$ 23,643
Accrued bonus	3,388	2,995
Income tax payable	987
Professional fees	808	539
Accrued vacation	797	513
Accrued payroll	795	596
Accrued severance		29
Other	2,369	1,946
Total accrued expenses	$ 52,441	$ 30,261

Warrant - Additional Information (Details) - Janssen Agreement - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2017
Class Of Warrant Or Right [Line Items]
Warrant to purchase common stock, shares		509,611
Exercise price		$ 9.81
Fair value of warrant at issuance	$ 3.4
Warrant expiration date	Feb. 09, 2022

Stockholders' Equity - Additional Information (Details)				1 Months Ended	2 Months Ended	12 Months Ended
Stockholders' Equity - Additional Information (Details)	Feb. 21, 2017 shares	Mar. 06, 2014	Dec. 23, 2013 USD ($) $ / shares shares	May 31, 2016 USD ($)	Mar. 12, 2018 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 shares	Mar. 25, 2014 shares	Feb. 28, 2014 shares
Class of Stock [Line Items]
Common stock, shares authorized						175,000,000	175,000,000
Common stock, par value \| $ / shares						$ 0.00001	$ 0.00001
Common stock, shares issued						47,612,619	38,615,709
Common stock, shares outstanding						47,612,619	38,615,709
Preferred stock, shares authorized						25,000,000	25,000,000
Preferred stock, par value \| $ / shares						$ 0.00001	$ 0.00001
Preferred stock, shares issued						0	0
Preferred stock, shares outstanding						0	0
Stock split, conversion ratio		1.75
Convertible redeemable preferred stock converted into common stock									0	12,115,183
Proceeds from the issuance of common stock, net of issuance costs \| $						$ 114,580,000	$ 66,736,000	$ 82,750,000
Granted, Shares						1,332,400
Shares remain eligible to vest						2,085,226
Common stock, shares reserved for future issuance						7,341,253	5,523,127
Stock-based compensation expense \| $						$ 12,280,000	$ 5,825,000	$ 4,714,000
Granted, Weighted-Average Grant Date Fair Value \| $ / shares						$ 8.47	$ 5.22	$ 6.07
Intrinsic value of options exercised \| $						$ 2,689,563	$ 600,000	$ 2,000,000
Fair value of options vested \| $						$ 5,600,000	4,600,000	3,200,000
2016 Inducement Award Program
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued						700,000
Granted, Shares						525,500
Shares remain eligible to vest						508,500
Common stock, shares reserved for future issuance						0
2016 Inducement Award Program \| Employees
Class of Stock [Line Items]
Granted, Shares						525,500
Restricted Stock Units
Class of Stock [Line Items]
Granted shares of restricted stock	423,650					449,900
Stock-based compensation expense \| $						$ 2,021,000	780,000	62,000
Granted, Weighted-Average Grant Date Fair Value \| $ / shares						$ 10.34
Weighted average period of recognition for unrecognized compensation costs						1 year 10 months 28 days
Forfeited, Weighted-Average Grant Date Fair Value \| $ / shares						$ 8.96
Unrecognized compensation cost \| $						$ 4,000,000
Restricted Stock Units \| Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage						100.00%
Stock Options
Class of Stock [Line Items]
Shares issued	719,400
Stock-based compensation description						Options vest in installments of (i) 25% at the one year anniversary and (ii) in either 36 or 48 equal monthly installments beginning in the thirteenth month after the initial vesting commencement date or 12 equal quarterly installments beginning on the first day of each calendar quarter after the initial vesting commencement date or grant date, subject to the individual’s continuous service with the Company.
Options expiration after the date of grant						10 years
Stock-based compensation expense \| $						$ 6,512,000	4,674,000	3,660,000
Stock Options \| Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage						25.00%
Restricted Stock
Class of Stock [Line Items]
Vesting periods			1 year
Stock-based compensation expense \| $						$ 158,000	266,000	$ 909,000
Forfeited, Weighted-Average Grant Date Fair Value \| $ / shares			$ 7.42			$ 7.42
Restricted stock requisite service period description						The awards of restricted stock contained a performance condition wherein the vesting commencement day was contingent upon the Company’s consummation of a liquidity event, as defined, prior to the fifth anniversary of the date of grant. Certain of the awards of restricted stock had a requisite service period that was complete upon grant. The remainder of the awards of restricted stock had a requisite service period of four years whereby the award vested 25% on the one year anniversary of a specified vesting commencement date, then ratably on the first day of each calendar quarter for 12 quarters, subject to continuous service by the individual and achievement of the performance target.
Grant-date fair value of restricted stock issued \| $			$ 3,900,000
Award requisite service period			4 years
Unrecognized compensation cost \| $						$ 0
Restricted Stock \| Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage			25.00%
Restricted Stock \| Employees
Class of Stock [Line Items]
Granted shares of restricted stock			450,224
Restricted Stock \| Non Employees
Class of Stock [Line Items]
Granted shares of restricted stock			79,067
Stock-based compensation expense \| $						$ 132,154	$ 3,000
Common Stock
Class of Stock [Line Items]
Common stock, shares outstanding						47,612,619	38,615,709	30,662,218	20,370,624
Issuance of common stock, net of issuance costs, shares						8,672,270	7,865,293	10,083,070
Maximum \| Restricted Stock Units
Class of Stock [Line Items]
Vesting periods						3 years
Maximum \| Stock Options
Class of Stock [Line Items]
Vesting periods						48 months
Minimum \| Restricted Stock Units
Class of Stock [Line Items]
Vesting periods						1 year
Minimum \| Stock Options
Class of Stock [Line Items]
Vesting periods						12 months
At The Market Equity Offering Program \| Common Stock
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares						465,615	615,293
Proceeds from the issuance of common stock, net of issuance costs \| $						$ 6,400,000	$ 5,700,000
At The Market Equity Offering Program \| Common Stock \| Scenario, Forecast
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares					694,306
Proceeds from the issuance of common stock, net of issuance costs \| $					$ 10,500,000
At The Market Equity Offering Program \| Maximum
Class of Stock [Line Items]
Common stock sales agreement amount \| $				$ 75,000,000
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance						1,790,600	1,140,328				1,785,000
Incremental rate at which the shares reserved for issuance increase						3.00%
2014 Plans \| Employees
Class of Stock [Line Items]
Granted, Shares						719,400
2014 Plans \| Director
Class of Stock [Line Items]
Granted, Shares						87,500
2014 Plans \| Restricted Stock Units \| Employees
Class of Stock [Line Items]
Granted shares of restricted stock						449,900
2014 Plans \| Inducement Award Program
Class of Stock [Line Items]
Compensation not yet recognized, stock options \| $						$ 13,000,000
Weighted average period of recognition for unrecognized compensation costs						2 years 8 months 19 days
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued						262,500
Percentage of increase on common stock authorized on each anniversary						1.00%
Number of common stock outstanding						739,611
Common stock shares authorized percentage under the plan						5.00%
Purchase price at the end of offering period						85.00%
Offering period						6 months
Shares issued						44,789
Stock-based compensation expense \| $						$ 200,000	$ 100,000

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	7,341,253	5,523,127
Warrant To Purchase Common Stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	509,611
Stock Options and Restricted Stock Units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	4,388,752	3,579,694
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	1,790,600	1,140,328	1,785,000
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	652,290	803,105

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Parenthetical) (Details) - shares	Jan. 01, 2018	Feb. 28, 2017	Jan. 01, 2017	Feb. 28, 2016	Jan. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance						7,341,253	5,523,127
2016 Inducement Award Program
Class of Stock [Line Items]
Common stock, shares reserved for future issuance						0
2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance			1,265,863		986,800
Common stock, shares reserved for future issuance						1,790,600	1,140,328	1,785,000
Subsequent Event \| 2016 Inducement Award Program
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	750,000
Subsequent Event \| 2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance	1,575,329
Employee Stock Purchase Plan
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance		0		273,404
Common stock, shares reserved for future issuance						652,290	803,105

Stockholders' Equity - Schedule of Assumptions Used in Black-Scholes Option Pricing Model (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.81%	1.16%	1.44%
Volatility	78.57%	64.78%	62.47%
Expected term (years)	5 years 6 months 3 days	5 years 6 months 3 days	5 years 6 months 3 days
Stock Options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.27%	2.03%	1.95%
Volatility	85.81%	82.40%	81.25%
Expected term (years)	6 years 3 months	6 years 3 months	6 years 3 months

Stockholders' Equity - Schedule of Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share under option
Outstanding beginning balance, Shares	3,148,006
Granted, Shares	1,332,400
Exercised, Shares	(291,439)
Forfeited, Shares	(528,953)
Outstanding ending balance, Shares	3,660,014	3,148,006
Options exercisable at end of period, Shares	1,574,788
Expected to vest at end of period, Shares	2,085,226
Weighted Average-Exercise Price
Outstanding beginning balance, Weighted-Average Exercise Price	$ 8.93
Granted, Weighted-Average Exercise Price	11.95
Exercised, Weighted-Average Exercise Price	5.28
Forfeited, Weighted-Average Exercise Price	14.80
Outstanding ending balance, Weighted-Average Exercise Price	9.47	$ 8.93
Options exercisable at end of period, Weighted-Average Exercise Price	7.62
Expected to vest at end of period, Weighted-Average Exercise Price	$ 10.88
Weighted-Average Remaining Contractual Term
Outstanding ending balance, Weighted-Average Contractual Life(in years)	8 years
Options exercisable at end of period, Weighted-Average Contractual Life(in years)	6 years 10 months 6 days
Aggregate Intrinsic Value
Outstanding, Aggregate Intrinsic Value	$ 21,932,858	$ 10,437,947
Exercised, Aggregate Intrinsic Value	2,689,563	$ 600,000	$ 2,000,000
Forfeited, Aggregate Intrinsic Value	1,502,894
Options exercisable at end of period, Aggregate Intrinsic Value	$ 12,971,099

Stockholders' Equity - Summary of Company Restricted Stock Activity (Details) - $ / shares			12 Months Ended
	Feb. 21, 2017	Dec. 23, 2013	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted stock activity, Shares
Granted, Weighted-Average Grant Date Fair Value			$ 8.47	$ 5.22	$ 6.07
Restricted Stock
Restricted stock activity, Shares
Restricted shares, Unvested beginning balance, Shares			92,972
Vested, Shares			(90,566)
Forfeited, Shares			(2,406)
Restricted shares, Unvested ending balance, Shares				92,972
Restricted shares, Unvested beginning balance, Weighted-Average Grant Date Fair Value			$ 8.08
Vested, Weighted-Average Grant Date Fair Value			8.56
Forfeited, Weighted-Average Grant Date Fair Value		$ 7.42	$ 7.42
Restricted shares, Unvested ending balance, Weighted-Average Grant Date Fair Value				$ 8.08
Restricted Stock Units
Restricted stock activity, Shares
Restricted shares, Unvested beginning balance, Shares			431,688
Granted, Shares	423,650		449,900
Vested, Shares			(26,000)
Forfeited, Shares			(126,850)
Restricted shares, Unvested ending balance, Shares			728,738	431,688
Restricted shares, Unvested beginning balance, Weighted-Average Grant Date Fair Value			$ 7.96
Granted, Weighted-Average Grant Date Fair Value			10.34
Vested, Weighted-Average Grant Date Fair Value			7.70
Forfeited, Weighted-Average Grant Date Fair Value			8.96
Restricted shares, Unvested ending balance, Weighted-Average Grant Date Fair Value			$ 9.26	$ 7.96

Stockholders Equity - Compensation Cost Related to Share-Based Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 12,280	$ 5,825	$ 4,714
Research and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	6,496	2,136	2,079
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,784	$ 3,689	$ 2,635

Stockholders Equity - Schedule of Compensation Expense by Type of Award (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 12,280	$ 5,825	$ 4,714
Warrants
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,413
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	6,512	4,674	3,660
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	158	266	909
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,021	780	62
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 176	$ 105	$ 83

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Line Items]
Current income tax expense			$ 0	$ 0
Deferred income tax expense		$ 0	0	0
Increase (decrease) in valuation allowance, deferred tax assets		(4,900,000)	56,400,000
Deferred capitalized start up expense net of amortization		800,000	900,000
Deferred income tax amortization		$ 1,100,000	1,000,000
NOL and R&D tax credit carry forward expiration year		2037
Changes in ownership interest rate period		3 years
Cumulative changes in ownership interest of shareholders		50.00%
Unrecognized tax benefits		$ 0	0	0
Income tax penalties and interest accrued associated with unrecognized tax benefits		0	0	0
Income tax penalties and interest expense associated with unrecognized tax benefits		$ 0	$ 0	$ 0
Federal tax at statutory rate		34.00%	34.00%	34.00%
Tax Cuts and Jobs Act of 2017 change in tax rate reduction in deferred tax asset and corresponding valuation allowance		$ 43,000,000
Maximum
Income Tax Disclosure [Line Items]
Federal tax at statutory rate		35.00%
Scenario, Plan
Income Tax Disclosure [Line Items]
Federal tax at statutory rate	21.00%
Net Operating Loss
Income Tax Disclosure [Line Items]
Future offset taxable income			$ 170,000,000
ASU 2016-09 \| Net Operating Loss
Income Tax Disclosure [Line Items]
Increase (decrease) in valuation allowance, deferred tax assets		$ 1,300,000
Impact of restatement on opening retained earnings, net of tax		0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 179,700,000	234,500,000
Operating Loss Carryforwards Expiration Year		2036
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 74,600,000	$ 103,900,000
Operating Loss Carryforwards Expiration Year		2036
Federal and State \| Earliest Tax Year
Income Tax Disclosure [Line Items]
Tax years remain open and subject to examination		2014
Federal and State \| Latest Tax Year
Income Tax Disclosure [Line Items]
Tax years remain open and subject to examination		2016
Federal and State \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards		$ 25,700,000
Other Assets
Income Tax Disclosure [Line Items]
Alternative minimum tax receivable		1,000,000
Accrued Expenses
Income Tax Disclosure [Line Items]
Alternative minimum tax payable		$ 1,000,000

Income Taxes - Schedule of Components of Loss Before Income Taxes and Reconciliation of Statutory Federal Income Tax Rate to Provision for Income Taxes (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal tax at statutory rate	34.00%	34.00%	34.00%
State and local tax at statutory rate	3.80%	1.40%	3.00%
Research and development tax credits	11.90%	6.40%	0.40%
Equity compensation	(0.60%)	(0.20%)	(0.60%)
Alternative minimum tax	(1.30%)
Change in valuation allowance	6.90%	(41.60%)	(36.80%)
Impact of US tax reform	(54.70%)
Effective tax rate	0.00%	0.00%	0.00%

Income Taxes -Schedule of Significant Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Accrued expenses	$ 4,305	$ 2,170
Deferred revenue	32,093	12,157
Intangible assets	509	449
Restricted stock		45
Non-qualified stock options	3,129	2,963
Research and development credits	25,322	10,510
Net operating loss carryforward	42,335	84,372
Other	600	326
Total deferred tax assets	108,293	112,992
Less valuation allowance	(108,112)	(112,986)
Total deferred tax assets, net of valuation allowance	181	6
Deferred tax liabilities:
Fixed assets	(181)	(6)
Total deferred tax liabilities	(181)	(6)
Net deferred tax asset	$ 0	$ 0

Commitments and Contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) ft² Extension_Option	Dec. 31, 2016 USD ($)	Jul. 31, 2016 ft²
Commitments And Contingencies [Line Items]
Area of property leased \| ft²	3,384		45,362
Monthly lease payments	$ 242,000
Operating lease payments commencement date	Jan. 01, 2017
Landlord contributions accounted for deferred lease incentive	$ 2,169,920
Landlord contribution for leasehold improvements	$ 70,526
Sublease term	2 years
Frequency of sublease rent receivable	monthly
Sublease monthly rent receivable	$ 22,000
Operating lease obligations partially offset by future sublease payments	257,000
Rent expense associated with lease	3,200,000	$ 2,500,000
Contract cost incurred in research and development activities	52,400,000
Total remaining contract costs	$ 276,400,000
FibroGen, Inc. \| Minimum
Commitments And Contingencies [Line Items]
Expected appeal process period	2 years
FibroGen, Inc. \| Maximum
Commitments And Contingencies [Line Items]
Expected appeal process period	3 years
Office Space
Commitments And Contingencies [Line Items]
Lease expiration date	Sep. 11, 2026
Lease period, number of extension options \| Extension_Option	1
Lease extension period	5 years
Lab Space
Commitments And Contingencies [Line Items]
Lease expiration date	Nov. 30, 2021
Lease period, number of extension options \| Extension_Option	1
Lease extension period	2 years
Other Assets
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease	$ 1,280,857	1,280,857
Other Current Assets
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease	21,432	21,432
Other Liabilities
Commitments And Contingencies [Line Items]
Total security deposit liability in connection with sublease	21,432	$ 21,432
Lease Monthly Payments On Or About January 1 2017
Commitments And Contingencies [Line Items]
Monthly lease payments	$ 22,000

Commitments and Contingencies - Schedule of Future Minimum Payments Required Under Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2018	$ 3,579
Operating Lease, 2019	3,626
Operating Lease, 2020	3,675
Operating Lease, 2021	3,684
Operating Lease, 2022	3,307
Operating Lease, Thereafter	12,573
Operating Lease, Total	30,444
Lease Payments to be Received from Sublease, 2018	257
Lease Payments to be Received from Sublease, Total	257
Net Operating Lease Payments, 2018	3,322
Net Operating Lease Payments, 2019	3,626
Net Operating Lease Payments, 2020	3,675
Net Operating Lease Payments, 2021	3,684
Net Operating Lease Payments, 2022	3,307
Net Operating Lease Payments, Thereafter	12,573
Net Operating Lease Payments, Total	$ 30,187

Net Loss per Share - Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	4,898,363	3,672,666	2,447,776
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	509,611
Outstanding Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,660,014	3,148,006	2,206,635
Unvested Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share		92,972	216,716
Unvested Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	728,738	431,688	24,425

Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 87,316	$ 41,283	$ 28,520	$ 20,865	$ 1,535				$ 177,984	$ 1,535
Operating expenses	75,949	65,459	50,656	65,837	39,579	$ 36,182	$ 36,188	$ 26,046	257,901	137,995	$ 61,513
Loss from operations	11,367	(24,176)	(22,136)	(44,972)	(38,044)	(36,182)	(36,188)	(26,046)	(79,917)	(136,460)	(61,513)
Other income (expense), net	914	1,042	618	429	182	(126)	409	248
Net (loss)/income	$ 12,281	$ (23,134)	$ (21,518)	$ (44,543)	$ (37,862)	$ (36,308)	$ (35,779)	$ (25,798)	$ (76,914)	$ (135,747)	$ (60,716)
Net (loss)/income per share:
basic	$ 0.26	$ (0.49)	$ (0.53)	$ (1.15)
diluted	$ 0.25	$ (0.49)	$ (0.53)	$ (1.15)
Weighted-average number of common shares:
basic	47,353,166	46,938,618	40,819,957	38,759,221
diluted	49,719,548	46,938,618	40,819,957	38,759,221
Net loss per share —basic and diluted					$ (0.99)	$ (0.96)	$ (0.95)	$ (0.70)	$ (1.77)	$ (3.60)	$ (2.29)

Warrant	12 Months Ended
Warrant	Dec. 31, 2017
Warrant Disclosure [Abstract]
Warrant	7. Warrant In connection with the Janssen Agreement, in February 2017 the Company issued a warrant to purchase 509,611 shares of the Company’s common stock at an exercise price of $9.81 per share. The warrant was fully vested upon issuance and exercisable in whole or in part, at any time prior to the fifth anniversary of the date of issuance. The warrant satisfied the equity classification criteria of ASC 815, and is therefore classified as an equity instrument. The fair value at issuance of $3.4 million was calculated using the Black-Scholes option pricing model and was charged to research and development expense as it represented consideration for a license for which the underlying intellectual property was deemed to have no alternative future use. As of December 31, 2017, the warrant remains outstanding and expires on February 9, 2022.

Employee Retirement Plan	12 Months Ended
Employee Retirement Plan	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
Employee Retirement Plan	11. Employee Retirement Plan During 2008, the Company established a retirement plan (the Plan) authorized by Section 401(k) of the Internal Revenue Code. In accordance with the Plan, all employees who have attained the age of 21 are eligible to participate in the Plan as of the first Entry Date, as defined, following their date of employment. Each employee can contribute a percentage of compensation up to a maximum of the statutory limits per year. Company contributions are discretionary and contributions in the amount of approximately $0.2 million, $0.2 million and $0.1 million were made during the years ended December 31, 2017, 2016 and 2015, respectively.

Consolidated Statements of Stockholders' Equity (Parenthetical)	12 Months Ended
	Dec. 31, 2016 shares
Statement Of Stockholders Equity [Abstract]
Treasury shares retired	(8,643)