Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2016	Mar. 01, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2016
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		38,829,563
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 264,950,830

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 187,335	$ 49,778
Available for sale securities	73,008	88,676
Unbilled receivable	33,823
Prepaid expenses and other current assets	2,155	2,563
Total current assets	296,321	141,017
Property and equipment, net	2,612	540
Deferred offering costs		102
Other assets	1,283	1,281
Total assets	300,216	142,940
Current liabilities:
Accounts payable	2,039	2,313
Accrued expenses	30,261	9,555
Short-term deferred revenue	81,968
Total current liabilities	114,268	11,868
Deferred rent	2,480	69
Deferred revenue, net of current portion	115,321
Other non-current liabilities	27	5
Total liabilities	232,096	11,942
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized at December 31, 2016 and 31, 2015; 0 shares issued and outstanding at December 31, 2016 and 2015
Common stock: $0.00001 par value; 175,000,000 shares authorized at December 31, 2016 and 2015; 38,615,709 and 30,662,218 shares issued and outstanding at December 31, 2016 and 2015, respectively	0	0
Additional paid-in capital	365,298	292,783
Treasury stock, at cost, 0 shares at December 31, 2016 and 8,643 shares at December 31, 2015		(162)
Accumulated other comprehensive income (loss)	(42)	(234)
Accumulated deficit	(297,136)	(161,389)
Total stockholders' equity	68,120	130,998
Total liabilities and stockholders' equity	$ 300,216	$ 142,940

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
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	38,615,709	30,662,218
Common stock, shares outstanding	38,615,709	30,662,218
Treasury stock, shares	0	8,643

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Collaboration revenue	$ 1,535
Operating expenses:
Research and development	115,785	$ 43,016	$ 23,263
General and administrative	22,210	18,497	14,677
Total operating expenses	137,995	61,513	37,940
Operating loss	(136,460)	(61,513)	(37,940)
Other income (expense):
Interest income	901	510	206
Other income	(188)	287	700
Net loss	(135,747)	(60,716)	(37,034)
Reconciliation of net loss to net loss applicable to common shareholders:
Net loss	(135,747)	(60,716)	(37,034)
Accretion on preferred stock			(86,899)
Net loss applicable to common stockholders - basic and diluted	$ (135,747)	$ (60,716)	$ (123,933)
Net loss per share applicable to common stockholders - basic and diluted	$ (3.60)	$ (2.29)	$ (8.04)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted	37,716,949	26,469,170	15,406,386
Comprehensive loss:
Net loss	$ (135,747)	$ (60,716)	$ (37,034)
Other comprehensive income (loss) - unrealized gain (loss) on securities	(42)	(234)	(56)
Comprehensive loss	$ (135,789)	$ (60,950)	$ (37,090)

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO	Common Stock	Additional Paid-In Capital	Additional Paid-In Capital IPO	Treasury Stock	Unrealized Gain/Loss	Accumulated Deficit	Series A, Series B and Series C Redeemable Convertible Preferred Stock
Balance at Dec. 31, 2013	$ (127,072)							$ (127,072)
Balance, shares at Dec. 31, 2013			1,383,345
Balance at Dec. 31, 2013									$ 157,827
Balance, shares at Dec. 31, 2013									5,324,948
Issuance of common stock, net of issuance costs	114,954			$ 114,954
Issuance of common stock, net of issuance costs, shares			6,762,000
Issuance of restricted common stock, shares			56,000
Forfeitures of restricted common stock, shares			(53,835)
Receipt of payment on promissory notes issued in exchange for shares of common stock	237			237
Exercise of options, shares			116,394
Exercise of options	89			89
Accretion of preferred stock to redemption value									$ 86,900
Accretion of preferred stock to redemption value	(86,900)			(85,663)				(1,237)
Conversion of preferred stock	244,727			180,057				64,670	$ (244,727)
Conversion of preferred stock, shares			12,115,183						(5,324,948)
Share-based compensation expense	6,010			6,010
Deferred offering costs- IPO		$ (10,715)			$ (10,715)
Unrealized gain/loss	(56)						$ (56)
Treasury shares purchased, not retired (2,553)	(94)					$ (94)
Treasury shares purchased, not retired in shares			(2,553)
Treasury shares purchased, retired	(68)					(68)
Treasury shares purchased, retired in shares			(5,910)
Net income (loss)	(37,034)							(37,034)
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, shares			218,674
Exercise of options	130			130
Share-based compensation expense	4,714			4,714
Unrealized gain/loss	(178)						(178)
Net income (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		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, shares	86,625		86,625
Exercise of options	$ 124			124
Share-based compensation expense	5,825			5,825
Unrealized gain/loss	$ 192						192
Treasury shares purchased, retired				(162)		162
Treasury shares purchased, retired in shares	(8,643)
Net income (loss)	$ (135,747)							(135,747)
Balance at Dec. 31, 2016	$ 68,120			$ 365,298		$ 0	$ (42)	$ (297,136)
Balance, shares at Dec. 31, 2016	38,615,709		38,615,709

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net loss	$ (135,747)	$ (60,716)	$ (37,034)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	296	96	49
Amortization of premium/discount on investments	494	558	268
Loss on disposal of property and equipment	306
Stock-based compensation	5,825	4,714	6,010
Changes in operating assets and liabilities:
Unbilled receivable	(33,823)
Prepaid expenses and other current assets	428	(1,001)	(686)
Other long-term assets	(2)	(976)	(179)
Accounts payable	(274)	231	1,307
Accrued expense	20,703	4,646	2,754
Deferred revenue	197,289
Deferred rent	2,411	41	28
Net cash provided by (used in) operating activities	57,906	(52,407)	(27,483)
Investing activities:
Purchase of equipment	(2,662)	(414)	(229)
Proceeds from the maturities of available for sale securities	162,376	63,901	12,585
Purchase of available for sale securities	(147,009)	(77,175)	(77,708)
Net cash provided by (used in) investing activities	12,705	(13,688)	(65,352)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	66,736	82,750	104,328
Proceeds from the sale of stock under employee stock purchase plan	106	220
Proceeds from the exercise of stock options	124	130
Repurchase of treasury stock			(162)
Payments received on promissory notes issued in exchange for shares of common stock			237
Payments on capital lease obligations	(20)	(7)	(3)
Net cash provided by financing activities	66,946	83,093	104,400
Increase in cash and cash equivalents	137,557	16,998	11,565
Cash and cash equivalents at beginning of the period	49,778	32,780	21,215
Cash and cash equivalents at end of the period	187,335	49,778	32,780
Non-cash financing activities
Conversion of series A, series B and series C preferred stock into common stock			244,727
Accretion of preferred stock to redemption value			$ 86,899
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, 2016
Accounting Policies [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Incorporated in Delaware in 2007, Akebia Therapeutics, Inc. (Akebia, or the Company) is a biopharmaceutical company focused on developing and delivering novel therapeutics for patients based on hypoxia-inducible factor, or HIF, biology, and building our pipeline while leveraging its development and commercial expertise in renal disease. HIF is the primary regulator of the production of red blood cells (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 a HIF-PH inhibitor in Phase 3 development, which has the potential to set a new standard of care in the treatment of anemia associated with chronic kidney disease (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 address serious diseases. The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates and undertaking preclinical and clinical studies. 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 regulatory 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 vadadustat Phase 3 program in non-dialysis dependent (NDD)-CKD, called PRO₂TECT, and dialysis depended (DD) CKD, called INNO₂VATE. In December 2015 the first patient was dosed in PRO₂TECT, and the first patient was dosed in INNO₂VATE in August 2016. Overall, the PRO₂TECT and INNO₂VATE Phase 3 programs are designed to enroll approximately 5,700 patients. The Company has engaged Quintiles as our primary CRO for the PRO₂TECT and INNO₂VATE programs. We expect the cost of the PRO₂TECT and INNO₂VATE programs to be in the range of $80,000 to $85,000 per patient, aggregating in the range of $456.0 million to $484.5 million in external CRO costs for the total program. These estimated costs could increase significantly if the Phase 3 program takes longer to complete or if we choose to add additional investigative sites, add additional patients, modify the clinical trial protocol, or perform other studies in support of the Phase 3 program. The enrollment numbers and the completion of the Phase 3 program will be driven by the assessment of major adverse cardiovascular events, or MACE. If the results of the Phase 3 program support the results observed across our previous 15 clinical studies, and the observed event rate is consistent with expectations, the Company anticipates submitting a New Drug Application (NDA) to the Food and Drug Administration (FDA) for vadadustat in the treatment of anemia associated with CKD for each indication in 2019. The Company is also subject to a number of other risks including possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, the development of new technological innovations by competitors, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and uncertainty around intellectual property matters. If the Company does not successfully commercialize any of its products, it will be unable to generate product revenue or achieve profitability. Through 2016 we have raised approximately $254.1 million of net proceeds from five underwritten public offerings, including $61.0 million of net proceeds raised in January 2016 whereby we sold 7,250,000 shares of common stock at a price of $9.00 per share and $5.7 million of net proceeds whereby we sold 615,293 shares of common in an at-the-market offering, or ATM, pursuant to a Sales Agreement with Cantor Fitzgerald & Co. entered into in May 2016. In December 2015, the Company entered into a collaboration agreement with Mitsubishi Tanabe Pharma Corporation, or MTPC, to develop and commercialize vadadustat in Japan and certain other countries in Asia for total payments of up to $350.0 million to fund the vadadustat Phase 3 program, including up to $100.0 million in upfront and development payments, of which $40.0 million was received in January 2016. To the extent Japanese patients are included in the Phase 3 Program, MTPC will fund up to an additional $60.0 million of development costs. If Japanese patients are not included in the Phase 3 Program, MTPC will be responsible for the costs of the local Phase 3 study in Japan and will make no additional funding payments for the Phase 3 Program, and $20.0 million of the $40.0 million the Company received in 2016 would be used to fund local development of vadadustat in Japan or be refunded to MTPC, at MTPC’s discretion. In December 2016, we entered into a collaboration and license agreement with Otsuka to develop and commercialize vadadustat in the United States. In December 2016, we received $125.0 million upfront payment and in March 2017, Otsuka reimbursed us 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 $106.2 million or more (depending on the actual global development costs incurred). In addition, if the development costs exceed a certain threshold, Akebia may require Otsuka to pay a higher percentage of the global development costs. In such event, Otsuka would be reimbursed for such additional funding out of milestone payments and net sales of vadadustat in the Territory. In addition, Akebia is eligible to receive from Otsuka up to $765.0 million in specified development and 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. In February 2017, we entered into a Research and License Agreement with Janssen, the Agreement, pursuant to which Janssen granted us an exclusive, license under certain intellectual property rights to develop and commercialize worldwide certain HIF prolyl hydroxylase-targeted compounds. Under the terms of the Agreement, Janssen granted us a license for a three-year research term to conduct research on the HIF compound portfolio, unless we elect to extend such research term for up to two additional one-year periods upon payment of an extension fee. During the research term, we may designate one or more compounds as candidates for development and commercialization. Once a compound is designated for development and commercialization, we will be solely responsible for the development and commercialization of the compound worldwide at our own cost and expense. The Agreement includes a license to develop and commercialize JNJ5169, a preclinical compound in development as an oral treatment for inflammatory bowel disease. Under the terms of the Agreement, we will pay an upfront payment of $1.0 million to Janssen within 30 days of execution of the Agreement. In addition, Janssen could be eligible to receive up to an aggregate of $16.5 million from us in specified development milestone payments on a product-by-product basis. Janssen will also be eligible to receive up to $215.0 million from us 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. The Company believes that it can continue as a going concern as its cash resources of approximately $260.3 million at December 31, 2016, together with the committed funding from its collaboration partners, including approximately $33.8 million received from Otsuka in March 2017, will be sufficient to allow the Company to fund its current operating plan into mid-2018, and as a result, through at least twelve months from the filing of the Company’s 2016 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. We will require additional capital for the further development of our existing product candidates and will need to raise additional funds sooner to pursue development activities related to additional product candidates. If and until we can generate a sufficient amount of revenue from our products, we expect to finance future cash needs through public or private equity, debt offerings, or strategic transactions. Unless otherwise indicated, all information in these consolidated financial statements gives retrospective effect to the 1.75-for-1 stock split of the Company’s common stock (the Stock Split) that was effected on March 6, 2014 (see Note 6), as well as any other stock-splits in historical periods.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2016

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 condensed 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 December 31, 2015, the Company identified and corrected an error in the historical classification of certain operating costs between research and development and general and administrative expenses. The Company concluded the effect of this classification error was not material to its consolidated financial statements for any prior period. The classification correction had no effect on the Company’s current or historical total operating expenses or net loss.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the FASB or other standard-setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting, as part of its Simplification Initiative. The areas for simplification in this update involve several aspects of 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. Some of the areas for simplification apply only to nonpublic entities. The amendments in ASU 2016-09 are effective for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years. Early application is permitted for all entities. The Company is currently evaluating the impact of this new standard on its consolidated financial statements.

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 lessees to recognize leases on their balance sheets, and leaves lessor accounting largely unchanged. The amendments in this ASU are effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early application is permitted for all entities. 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.

In November 2015, the FASB issued ASU No. 2015-17, to simplify the presentation of deferred income taxes. The new standard requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. The standard is effective for interim and annual periods beginning after December 15, 2016 and allows for early adoption using a full retrospective method or a prospective method for all periods presented. The Company elected to early adopt the provisions of this new standard in the fourth quarter of 2015 using a full retrospective method. The accounting standard did not have any impact on the Company’s consolidated financial statements since a full valuation allowance has been provided on the Company’s deferred tax assets (see Note 7).

In August 2014, the FASB issued ASU 2014-15, which requires management of public and private companies to evaluate whether there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. If conditions or events raise substantial doubt about an entity’s ability to continue as a going concern, and substantial doubt is not alleviated after consideration of management’s plans, an entity should include a statement in the footnotes indicating that there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. The new standard is effective for annual periods ending after December 15, 2016, and for annual periods and interim periods thereafter. The Company adopted the standard in the fourth quarter of 2016. See Note 1 for additional information on our liquidity risks and management’s plans.

In May 2014, the FASB, issued 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 is 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 or a modified retrospective method. The Company’s historical revenue has been derived from its collaboration agreements with MTPC and Otsuka. These arrangements contain multiple-elements and have been accounted for pursuant to ASC 605-25. As of December 31, 2016, the Company has not commenced revenue recognition under the MTPC arrangement as the Company is not yet able to determine all of its deliverables and the total amount of arrangement consideration. The new revenue standard provides guidance in assessing what comprises the distinct service being provided to a customer that may have implications to our performance obligations and unit of account identified in our two existing collaborations which could be defined differently under the new guidance. As a result, there could be changes to the timing of revenue recognition upon adoption of the new standard. The Company is currently assessing the impact of the new revenue recognition standard on its two collaboration agreements and evaluating which method it will use to adopt.

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 proprietary therapeutics based on HIF biology.

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, accrued expenses, revenue and income taxes.

Prior to the initial public offering, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company granted stock options at exercise prices not less than the fair market value of its common stock as determined by the Board of Directors contemporaneously at the date such grants were made, with input from management. Prior to the Company’s initial public offering in March 2014, the fair value of common stock at the grant date was adjusted in connection with the Company’s retrospective fair value assessment for financial reporting purposes. Accordingly, the Board of Directors determined the estimated fair value of the Company’s common stock based on a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector and the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale of the Company.

The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its common stock in periods prior to March 2014. The methodologies included a probability analysis including both a potential public trading scenario and potential sale scenario. In both scenarios, value is estimated using the guideline public company method. The sale scenario includes an adjustment for a market participant acquisition premium. Value is allocated among the preferred and common shares according to the rights associated with each type of security. Valuation methodologies include estimates and assumptions that require the Company’s judgment. These estimates include assumptions regarding future performance, including the successful completion of a public offering. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date.

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. At December 31, 2016, the Company’s cash is 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, 2016. 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.

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 9) and any other collaborations the Company may enter into.

Multiple-Element Arrangements

The Company recognizes revenue in accordance with ASC Topic 605, Revenue Recognition (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 will commence when all criteria as required under SC 605 have been satisfied. Therefore, collaboration revenue in 2016 is generated exclusively from its collaboration arrangement with Otsuka. The terms of this arrangement 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 this arrangement include: (i) up-front fee, (ii) payments for development services and (iii) payments based on the achievement of certain milestones. Also, 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 collaboration with Otsuka. The Company will recognize 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 Topic 605‑25, Revenue Recognition Multiple‑Element Arrangements (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 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 (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 (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 collaboration with Otsuka as a component of the related expense in the period incurred. To the extent 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.

Income Taxes

Income taxes are recorded in accordance with FASB Topic 740, Income Taxes (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. The Company elected to early adopt the provisions of ASU No. 2015-17 in the fourth quarter of 2015 using a full retrospective method. As a result, all deferred taxes as of December 31, 2016 and 2015 are classified as noncurrent within the income tax provision (see Note 7), however as we record a full valuation allowance against the Company’s net deferred tax assets, the adoption of this standard has no impact on our consolidated balance sheets as of December 31, 2016 and 2015.

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, 2016 and 2015, 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 FASB ASC Topic 718, Compensation—Stock Compensation (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 FASB ASC Topic 505-50, Equity-Based Payments to Non-Employees (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 and shares of common stock. The Company estimates the fair value of options granted using the Black-Scholes option pricing model. The Company uses 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. The Company is in the product development stage with no 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 is also required to estimate forfeitures at the time of grant, and revise those estimates in the subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate pre-vesting forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the difference is recorded as a cumulative adjustment in the period the estimates were revised. Stock-based compensation expense recognized in the condensed consolidated financial statements is based on awards that are ultimately expected to vest.

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. FASB ASC Topic 820, Fair Value Measurements and Disclosures (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 4). 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 and investments are the only financial instruments that potentially subject the Company to concentrations of credit risk. The Company maintains its cash with high quality, accredited financial institutions and, accordingly, such funds are subject to minimal 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.

Net Loss per Share

Basic net loss per share is calculated by dividing net loss attributable to common stockholders 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, unvested 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.

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, 2016 and 2015.

	Useful Life	December 31, 2016			December 31, 2015
		(in thousands)
Computer equipment and software	3	$	476		$	300
Furniture and fixtures	5		729			243
Equipment	7		50			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		1,763			70
Office equipment under capital lease	3		36			24
			3,054			687
Less accumulated depreciation			(442	)		(147	)
Net property and equipment		$	2,612		$	540

Depreciation expense, including expense associated with assets under capital leases, was approximately $295,000, $96,000 and $49,000 for the years ended December 31, 2016, 2015 and 2014, respectively.

Available for Sale Securities

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Available for Sale Securities

3. Available for sale securities

Available for sale securities at December 31, 2016 and 2015 consist of the following:

			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

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2015
Cash and cash equivalents	$	49,778	$	—	$	—		$	49,778
Available for sale securities:
Certificates of deposit	$	21,505	—			—		$	21,505
U.S. Government debt securities		46,461	—			(185	)		46,276
Corporate debt securities		20,944		1		(50	)		20,895
Total available for sale securities	$	88,910	$	1	$	(235	)	$	88,676
Total cash, cash equivalents, and available for sale securities	$	138,688	$	1	$	(235	)	$	138,454

The estimated fair value of the Company’s available-for-sale securities balance at December 31, 2016, by contractual maturity, is as follows:

Due in one year or less	$	65,071
Due after one year		7,937
Total available for sale securities	$	73,008

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2016

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

4. 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 December31, 2016 are summarized below:

	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

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2015 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2015
Assets:
Cash and cash equivalents	$	49,778	$	—	$	—	$	49,778
Certificates of deposit		—		21,505		—		21,505
U.S. Government debt securities		—		46,276		—		46,276
Corporate debt securities		—		20,895		—		20,895
	$	49,778	$	88,676	$	—	$	138,454

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, 2016 and December 31, 2015.

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, 2016

Payables And Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses are as follows:


	December 31, 2016		December 31, 2015
	(in thousands)
Accrued clinical	$	23,643	$	4,536
Accrued bonus		2,995		2,178
Accrued payroll		596		518
Professional fees		539		647
Accrued vacation		513		310
Accrued severance		29	—
Other		1,946		1,366
Total accrued expenses	$	30,261	$	9,555

During 2016, the Company entered into separation agreements with three employees. During 2016, the Company recorded severance expense in the amount of $0.5 million, of which $0.2 million was recorded to general and administrative expense and $0.3 million was recorded to research and development expense. During the year ended December 31, 2016, approximately $0.4 million was paid out of the severance accrual. At December 31, 2016, approximately $29,000 remained in accrued expense in relation to the unpaid severance costs.

Stockholders' Equity

12 Months Ended

Dec. 31, 2016

Equity [Abstract]

Stockholders' Equity

6. Stockholders’ Equity

Authorized and Outstanding Capital Stock

As of December 31, 2014, the authorized capital stock of the Company included 175,000,000 shares of common stock, par value $0.00001 per share, of which 38,615,709 and 30,662,218 shares are issued and outstanding at December 31, 2016 and 2015, respectively; and 25,000,000 shares of undesignated preferred stock, par value $0.00001 per share, of which 0 shares are issued and outstanding at December 31, 2016 and December 31, 2015.

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.

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 IPO 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 rules, did not require shareholder approval (the 2016 program and similar programs, each and “Inducement Award Program”) under which 350,000 shares were reserved to be issued in 2016 and 255,000 shares were granted and remain eligible to vest. The Company expects to continue to grant inducement awards to new hires under a 2017 authorization.

The 2014 Plan allows for the granting of stock options, stock appreciation rights (SARs), restricted stock, unrestricted stock, stock units, 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, 2016, the Company granted 1,304,275 stock options to employees, of which 255,000 shares were under the Inducement Award Program, 450,838 restricted stock units (RSUs) to employees and 112,500 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 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, 2016		December 31, 2015
Common stock options and RSU's outstanding		3,579,694		2,231,057
Shares available for issuance under the 2014 Plan ⁽¹⁾		885,328		1,318,732
Shares available for issuance under the ESPP ⁽²⁾		803,105		440,304
Total		5,268,127		3,990,093

⁽¹⁾

On January 1, 2017 and January 1, 2016, the shares reserved for future grants under the 2014 Plan increased by 1,265,863 and 986,800 shares, respectively, pursuant to the 2014 Plan Evergreen Provision.

⁽²⁾

On February 28, 2017 and February 28, 2016, the shares reserved for future issuance under the ESPP increased by 388,296 and 379,430 shares, respectively, pursuant to the ESPP Evergreen Provision.

Stock-Based Compensation

Stock Options

On February 22, 2016, as part of the Company’s annual grant of equity, the Company issued 624,275 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 or 12 equal quarterly installments beginning in the thirteenth month 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 $4.7 million of stock-based compensation expense related to stock options during 2016.

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,
	2016		2015		2014
Risk-free interest rate	1.16% - 2.03%		1.44% - 1.95%		1.63% - 2.06%
Dividend yield		0.00%		0.00%		0.00%
Volatility	64.78% - 82.40%		62.47% - 81.25%		67.97% - 77.00%
Expected term (years)	5.51 - 6.25		5.51 - 6.25		6.25

The following table summarizes the Company’s stock option activity:

	Shares			Weighted-Average Exercise Price		Weighted-Average Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2015		2,206,635		$	9.04			$	13,114,811
Granted		1,416,775		$	8.11
Exercised		(86,625	)	$	1.43			$	623,686
Forfeited		(388,779	)	$	8.24			$	267,459
Expired/cancelled		—
Outstanding, December 31, 2016		3,148,006		$	8.93		8.06	$	10,437,947
Options exercisable, December 31, 2016		1,134,870		$	8.34		6.64	$	5,785,199
Expected to vest, December 31, 2016		2,805,675		$	9.31		8.27	$	8,759,055

As of December 31, 2016, there was approximately $9.6 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 2.46 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 vesting is 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 have a requisite service period that was complete upon grant. The remainder of the awards of restricted stock have a requisite service period of four years whereby the award vests 25% on the one year anniversary of the 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. Compensation expense related to the restricted stock awards is being recognized over the associated requisite service period which commenced on March 25, 2014, as a result of our IPO. The Company recorded approximately $0.3 million of stock-based compensation expense related to restricted stock during 2016, of which approximately $3,000 was as a result of mark to market adjustments related to non-employees.

A summary of the Company’s restricted stock activity is as follows:

	Shares			Weighted-Average Grant Date Fair Value
Restricted shares as of December 31, 2015		216,716		$	7.80
Granted		—
Vested		(108,688	)	$	7.71
Forfeited		(15,056	)	$	7.42
Restricted shares as of December 31, 2016		92,972		$	8.08

As of December 31, 2016, there was approximately $48,000 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. The unrecognized compensation cost is expected to be recognized over a weighted average period of 0.56 years.

Restricted Stock Units

On February 22, 2016, as part of the Company’s annual grant of equity, the Company issued 382,338 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 the third anniversary of the grant date, subject, in each case, to the individual’s continued service through the applicable vesting date. Total stock-compensation expense to be recognized over the life of the RSUs is $2.9 million and will be recognized on a straight-line basis over the vesting period. The Company recorded approximately $0.8 million of stock-based compensation expense related to the RSUs in 2016 .

	Shares			Weighted-Average Grant Date Fair Value
Unvested balance, December 31, 2015		24,425		$	11.15
Granted		450,838		$	7.83
Vested		—
Forfeited		(43,575	)	$	8.38
Outstanding, December 31, 2016		431,688		$	7.96

As of December 31, 2016, there was approximately $2.0 million of unrecognized compensation cost related to RSUs, which is expected to be recognized over a weighted average period of 2.11 years.

Employee Stock Purchase Plan

The first offering period under the ESPP opened on January 2, 2015. There were 16,629 shares issued during the year ended December 31, 2016. The Company recorded approximately $0.1 million of stock-based compensation expense related to the ESPP during 2016.

Compensation Expense Summary

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

	Years ended December 31,
	2016		2015		2014
	(in thousands)
Research and development	$	2,136	$	2,079	$	2,766
General and administrative		3,689		2,635		3,244
Total	$	5,825	$	4,714	$	6,010

Compensation expense by type of award:

	Years ended December 31,
	2016		2015		2014
	(in thousands)
Stock options	$	4,674	$	3,660	$	1,925
Restricted stock		266		909		4,085
Restricted stock units		780		62		—
Employee stock purchase plan		105		83		—
Total	$	5,825	$	4,714	$	6,010

Included in the compensation expense for the year ended December 31, 2014, is approximately $1.0 million related to the modification of awards in connection with an employee separation agreement in the first quarter of 2014.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Income Taxes

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income Taxes

7. Income Taxes

The Company’s income tax provision was computed based on the federal statutory rate and the state statutory rates, net of the related federal benefit. There was no current or deferred income tax expense or benefit for the years ended December 31, 2016, 2015 and 2014 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,
	2016			2015			2014
Federal tax at statutory rate		34.0	%		34.0	%		34.0	%
State and local tax at statutory rate		1.4			3.0			5.5
Research and development tax credits		6.4			0.4			(0.6	)
Equity compensation		(0.2	)		(0.6	)		(1.6	)
Other permanent differences and credits		—			—			(0.1	)
Change in valuation allowance		(41.6	)		(36.8	)		(37.2	)
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 increased by approximately $56.4 million and 22.3 million, during the years ended December 31, 2016 and 2015. Significant components of the Company’s deferred tax assets and liabilities are as follows:

		December 31,
		2016			2015
	(in thousands)
Deferred tax assets:
Accrued expenses		$	2,170		$	912
Deferred revenue			12,157			—
Intangible assets			449			527
Restricted stock			45			301
Fixed assets			—			—
Non-qualified stock options			2,963			1,558
Research and development credits			10,510			1,829
Net operating loss carryforward			84,372			51,356
Other			326			64
Total deferred tax assets			112,992			56,547
Less valuation allowance			(112,986	)		(56,545	)
Total deferred tax assets, net of valuation allowance			6			2
Deferred tax liabilities:
Fixed assets			(6	)		(2	)
Total deferred tax liabilities			(6	)		(2	)
Net deferred tax asset		$	—		$	—

At December 31, 2016 and December 31, 2015, the Company has approximately $0.9 million (after amortization of $1.0 million) and $1.0 million (after amortization of $0.9 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, 2016 and 2015, the Company has approximately $234.5 million and $140.5 million, respectively, of federal net operating loss (NOL) carry-forwards which expire through 2036. Additionally, at December 31, 2016 and 2015, the Company has approximately $103.9 million and $111.9 million, respectively, of state net operating loss (NOL) carry-forwards which expire through 2036. Included in the 2016 and 2015 NOLs are tax deductions related to equity compensation in excess of book compensation expense. Pursuant to the realization requirements in ASC 718, these tax deductions are not included in the NOL deferred tax asset above. The Company also has approximately $10.8 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 2036, 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, which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future. The Company has not yet analyzed whether there has been a change in control.

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, 2016, 2015 and 2014, 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 2013 through 2015 tax years remain open and subject to examination by federal and state taxing authorities. However, federal and state net operating losses from 2009 through 2015 are subject to review by taxing authorities in the year utilized.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. 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 for base rent are approximately $242,000 per month which is subject to annual rent escalations. In addition to such annual rent escalations, base rent payments for a portion of said premises are scheduled to commence on or about 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 $256,765 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 for the lab space is five years, 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 included in other assets in the Company’s condensed consolidated balance sheets as of December 31, 2016 and December 31, 2015.

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 condensed consolidated balance sheets as of December 31, 2016 and December 31, 2015. The Company will begin recognizing rent expense for the lab space and the remaining office space subsequent to taking possession of the space.

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 $0.5 million. The total security deposit in connection with the Sublease of $21,432 which is due within 30 days from the execution of the Sublease, is included in other current assets and other liabilities in the Company’s consolidated balance sheets.

The Company leases office equipment under three year capital leases with payments commencing in February 2014, April 2015 and February 2016, respectively. The capital lease amounts are included in accrued expenses and other liabilities.

At December 31, 2016, the Company’s future minimum payments required under these leases are as follows:

			Lease Payments
	Operating		to be Received		Net Operating		Capital
	Lease		from Sublease		Lease Payments		Lease		Total
	(in thousands)
2017	$	3,545	$	257	$	3,288	$	9	$	3,297
2018		3,545		257	$	3,288		5	$	3,293
2019		3,545		—	$	3,545		—	$	3,545
2020		3,545		—	$	3,545		—	$	3,545
2021		3,510		—	$	3,510		—	$	3,510
Thereafter		14,666		—	$	14,666		—	$	14,666
Total	$	32,356	$	514	$	31,842		14	$	31,856
Less amount representing interest								—
Present value of minimum lease payments at December 31, 2016							$	14

The Company recorded approximately $2.5 million and $0.9 million in rent expense for the years ended December 31, 2016 and 2015, respectively.

Under the Company’s agreement with a subsidiary of Quintiles IMS Holdings, Inc., or Quintiles, to provide services for the PRO₂TECT and INNO₂VATE programs, the total remaining contract costs as of December 31, 2016 were approximately $406.4 million. The estimated period of performance for the committed work with Quintiles is through the fourth quarter of 2019. The Company contracts with various other organizations to conduct research and development activities with remaining contract costs to the Company of approximately $24.9 million at December 31, 2016. 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.

In September 2015, a purported securities class action lawsuit was filed against the Company, including its Chief Executive Officer, its Chief Financial Officer, and members of the Company’s Board of Directors, in the Business Litigation Section of the Suffolk County Superior Court of Massachusetts. The complaint is brought on behalf of an alleged class of those who purchased common stock of the Company pursuant or traceable to the Company’s initial public offering, and purports to allege claims arising under Sections 11, 12(a)(2) and 15 of the Securities Act of 1933, as amended. The complaint generally alleges that the defendants violated the federal securities laws by, among other things, making material misstatements or omissions concerning the Phase 2b clinical study of vadadustat. The complaint seeks, among other relief, unspecified compensatory damages, rescission of certain stock purchases, attorneys’ fees, and costs. In October 2015, the Company removed the case to the United States District Court for the District of Massachusetts, and the plaintiff filed a motion to remand the case back to the Business Litigation Section of the Suffolk County Superior Court of Massachusetts. The plaintiff’s motion to remand was granted in April 2016. The plaintiff filed an amended complaint in the Suffolk County Superior Court on August 15, 2016, and the Company served a memorandum in support of its motion to dismiss the amended complaint on October 14, 2016. The motion to dismiss hearing was held on January 31, 2017. The Court granted the Company’s motion to dismiss and dismissed the case with prejudice on February 21, 2017. The plaintiff has 30 days to appeal the decision. The Company believes such claims are without merit and will engage in a vigorous defense of such appeal, if it is ultimately filed by the plaintiff.

The Company has had a number of positive developments in our opposition and invalidity proceedings against FibroGen, Inc., or FibroGen. With regard to the opposition that the Company filed in Europe against FibroGen’s European Patent No. 1463823, or the ’823 patent, 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. Likewise, with regard to the invalidity proceeding that the Company filed in Japan against certain claims of FibroGen’s Japanese Patent No. 4804131, or the ’131 patent, which is the Japanese counterpart to the ’823 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 FibroGen Japanese ’131 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 and ’131 patents. In the event FibroGen were to obtain such a patent in the United States, the Company may decide to challenge them like the Company has 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. 2322153, 2322155, and 1633333, or the ’153 patent, the ’155 patent, and the ’333 patent, respectively, 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 we do not believe these patents will prevent us from commercializing vadadustat for treatment of anemia secondary to CKD, we filed these oppositions to provide us and any future partners with maximum flexibility for developing vadadustat and our pipeline of HIF PH inhibitors. With regard to the opposition that we filed in Europe against FibroGen’s European Patent No. 163333, or the ’333 patent, an oral proceeding took place 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. FibroGen has appealed that decision. Oppositions to the ’155 patent and to the ’153 patent were also filed by Glaxo Group Limited, or Glaxo and by Bayer Intellectual Property GmbH, Bayer Pharma Aktiengesellschaft, and Bayer Animal Health GmbH. While, for the reasons set forth in our oppositions, the Company believes that the ’153 patent and the ’155 patent should be revoked in their entirety, the ultimate outcomes of the oppositions remains uncertain. If the European Patent Office decides not to revoke the ’153 patent or the ’155 patent in their entirety, or only certain claims of those patents, and any surviving claims are determined to encompass the Company’s intended use of the Company’s lead product candidate, the Company may not be able to commercialize the Company’s lead product candidate in the European Union for its intended use, which could materially adversely affect the Company’s business, operating results and financial condition.

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.

Significant Agreements	12 Months Ended
Significant Agreements	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Agreements	9. 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, the Company’s product candidate for the treatment of anemia related to chronic kidney disease, in Japan and certain other Asian countries, collectively, the Territory. Pursuant to the MTPC Agreement, MTPC has an exclusive license to develop and commercialize vadadustat in the Territory. In addition, the Company will supply vadadustat for both clinical and commercial use in the Territory. The countries included in the Territory are Japan, Taiwan, South Korea, Singapore, Malaysia, India, Indonesia, East Timor, Mongolia, the Philippines, Vietnam, Laos, Cambodia, Thailand, Brunei, Myanmar, Nepal, Sri Lanka, Bangladesh, Bhutan, Maldives, Palau and Tonga and their territories. In consideration for the exclusive license and other rights contained in the MTPC Agreement, MTPC will make payments totaling up to $350.0 million to fund the vadadustat Phase 3 program (Phase 3 Program), including up to $100.0 million in upfront and development payments, of which $40.0 million was received in January 2016. To the extent Japanese patients are included in the Phase 3 Program, MTPC will fund up to an additional $60.0 million of development costs (Global Scenario). If Japanese patients are not included in the Phase 3 Program (Local Scenario), MTPC will be responsible for the costs of the local Phase 3 study in Japan and make no additional funding payments for the Phase 3 Program. In addition, $20.0 million of the $40.0 million received in 2016 would be used to fund local development of vadadustat in Japan or be refunded to MTPC, at MTPC’s discretion. The final determination of whether Japanese patients can be included in the Phase 3 Program will be made by the Company and MTPC, in consultation with the Pharmaceuticals and Medical Devices Agency, PMDA, following the results of our Phase 2 studies being conducted in Japan, which is expected in the second half of 2017, unless the Company and MTPC otherwise collectively decide, as provided in the MTPC Agreement, to pursue the Local Scenario prior to such determination by the PMDA. The Company is also eligible to receive up to approximately $250.0 million in additional payments based upon achievement of certain development, regulatory and sales milestones, as well as tiered double-digit royalty payments on sales of vadadustat in the Territory. 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 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 total aggregate amount of development milestones is $10.0 million and the total aggregate amount of approval milestones is up to $65.0 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. 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. The Company and MTPC have established a joint steering committee to oversee development and commercialization of vadadustat in the 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 Territory; expiration of marketing or regulatory exclusivity in such country in the Territory; or ten years after the first commercial sale of vadadustat in such country in the 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. As of December 31, 2016, the Company cannot determine all of its deliverables or the total amount of consideration to be received for which revenue will be recognized until it knows whether vadadustat will be developed for the Japan market under a Global Scenario or under a Local Scenario. Given the uncertainty around both deliverables and the total consideration to be received, we concluded that we lack sufficient persuasive evidence of an arrangement until these uncertainties are resolved (that is, there is uncertainty regarding our rights and obligations under the arrangement). Under a Global Scenario, our deliverable will be a Services Deliverable as we will be required to include Japanese subjects in our ongoing global Phase 3 study. Under a Local Scenario, our deliverable will be a Supply Deliverable as we will not include Japanese subjects in our ongoing Phase 3 program, but will instead provide clinical supply of vadadustat to MTPC in order for MTPC to conduct a local study. The final determination will be made by the Company and MTPC in consultation with the PMDA following the results of our Phase 2 studies being conducted in Japan, unless the Company and MTPC otherwise decide to pursue the Local Scenario prior to such consultation with the PMDA. Revenue recognition for the MTPC Agreement will commence when all criteria as required under ASC 605 have been satisfied, which the Company expects will be in the second half of 2017. Therefore, the $40.0 million payment received in January 2016 is recorded as deferred revenue in the accompanying consolidated balance sheet. Otsuka Pharmaceutical Company. Ltd. Collaboration and License Agreement Summary of Agreement On December 18, 2016, the Company entered into a collaboration and license agreement with Otsuka, or the Otsuka Agreement. The collaboration is focused on the development and commercialization of vadadustat in the United States. Under the terms of the Otsuka 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 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 Agreement. Pursuant to the terms of the Otsuka 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 that are necessary through the filing of an NDA, including the ongoing PRO₂TECT program and the ongoing INNO₂VATE program, as well as other derivative and ancillary studies. Under the Otsuka 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 Agreement, the parties will jointly conduct, and will have equal responsibility for, all medical affairs, commercialization and non-promotional activities pursuant to underlying plans as agreed to by the parties. The Company will retain control over and responsibility for the manufacturing and supply of vadadustat during development. 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 Agreement will be governed by a joint steering committee (JSC) formed by an equal number of representatives from the Company and Otsuka. The JSC will coordinate and monitor the parties’ activities under the collaboration. Among other responsibilities, the JSC will manage the overall strategic alignment between the parties, oversee the current global development plan and review 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 will establish a joint development committee (JDC) which will be 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 (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 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 $106.2 million or more. 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. 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 $125.0 million in development milestone payments and up to $65.0 million in regulatory milestone payments for the first product to achieve the associated event. Moreover, the Company is eligible for up to $575.0 million in commercial milestone payments associated with aggregate sales of all products. Due to the uncertainty of pharmaceutical development and the high historical failure rates associated with drug development, no milestone payments may ever be received from Otsuka. Under the Otsuka 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 Agreement, Otsuka has 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). Upon Otsuka’s exercise of the Royalty Conversion Option, the licenses granted to Otsuka will terminate and the parties will cease joint participation in the collaboration. Effective immediately upon the exercise of the Royalty Conversion Option, the Company will be solely responsible for all future development, manufacturing, medical affairs and commercialization and non-promotional activities. Royalties that would be payable to Otsuka upon the exercise of the Royalty Conversion Option are subject to reduction upon the date on which vadadustat ceases to have exclusivity. Royalties would be due on a product-by-product and country-by-country basis from the date of the first commercial sale of vadadustat in such country until the fifth anniversary of the date on which the licensed product ceases to have exclusivity. Unless earlier terminated, the 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 Agreement in its entirety if the other party has materially breached its obligations under the agreement and, after receiving written notice identifying such material breach in reasonable detail, the breaching party fails to cure such material breach. Otsuka may terminate the Otsuka 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. If Otsuka exercises the Royalty Conversion Option and the Company subsequently exercises its right to buy-back the royalty obligation, then the Otsuka Agreement will automatically terminate in its entirety. In the event of termination of the Otsuka Agreement, all rights and licensees granted to Otsuka under the Otsuka 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 reimbursement to Otsuka. Accounting Analysis The Company determined that the medical affairs and commercialization and non-promotional activities elements of the License 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 commercial success of the activities. Accordingly, the Company is accounting for the joint medical affairs and commercialization and non-promotional activities in accordance with ASC No. 808, Collaborative Arrangements (ASC 808). Additionally, the medical affairs and commercialization and non-promotional activities were not deemed to be deliverables under ASC No. 605-25, Revenue Recognition–Multiple-Element Arrangements (ASC 605-25). As a result, the activities conducted pursuant to the medical affairs and commercialization and non-promotional activities plans will be accounted for as a component of the related expense in the period incurred. The Company evaluated the other elements of the License 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 R&D Development Services Deliverable), (iii) rights to future intellectual property and (iv) joint committee services. 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. Accordingly, each of the other deliverables included in the Otsuka arrangement qualifies as a separate unit of accounting. Therefore, the Company has identified the following three units of accounting in connection with its obligations under the collaboration arrangement with Otsuka as follows: (i) License and R&D Development Services Combined The License Deliverable does not have standalone value separate from the R&D 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 regulatory 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 The License Deliverable and the R&D Development Services deliverable have standalone value from the Rights to Future Intellectual Property 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. (iii)Joint Committee Services The Joint Committee Services has standalone value from the License and R&D Services deliverables 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 Joint Committee Services has standalone value from the Rights to Future Intellectual Property 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 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 $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 of $106.2 million. The cost share payments to be received represent contingent revenue features because the Company’s retention of the associated arrangement consideration is dependent upon its future performance of development services. 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 $265.0 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 License 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 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, 2016, the Company recognized revenue totaling approximately $1.5 million with respect to the License Agreement. The revenue is classified as collaboration revenue in the accompanying consolidated statement of operations. As of December 31, 2016, there is approximately $157.3 million of deferred revenue related to the License Agreement which is classified as current or long-term in the accompanying consolidated balance sheet based on the performance period of the underlying obligations. During the year ended December 31, 2016, the Company did not incur any costs related to the cost-sharing provisions of the License Agreement. In addition, as of December 31, 2016, the Company recorded a $33.8 million unbilled receivable related to the reimbursable development costs under the License Agreement for activities performed through December 31, 2016. The Company received payment of the $33.8 million in March 2017.

Employee Retirement Plan	12 Months Ended
Employee Retirement Plan	Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Employee Retirement Plan	10. 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, $0.1 million and $0 were made during the year ended December 31, 2016, 2015 and 2014, respectively.

Net Loss per Share

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Net Loss per Share

11. Net Loss per Share

The following table presents the calculation of basic and diluted net loss per share applicable to common stockholders:

	Year ended December 31,
	2016			2015			2014
	(in thousands, except share and per share data)
Numerator:
Net loss	$	(135,747	)	$	(60,716	)	$	(37,034	)
Accretion on preferred stock		—			—			(86,899	)
Net loss applicable to common stockholders	$	(135,747	)	$	(60,716	)	$	(123,933	)

Denominator:
Weighted-average number of common shares – basic and diluted		37,716,949			26,469,170			15,406,386
Net loss per share applicable to common stockholders – basic and diluted	$	(3.60	)	$	(2.29	)	$	(8.04	)

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,
	2016		2015		2014
Outstanding stock options		3,148,006		2,206,635		1,526,346
Unvested restricted stock		92,972		216,716		422,145
Unvested restricted stock units		431,688		24,425		—
Total		3,672,666		2,447,776		1,948,491

Quarterly Results (unaudited)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Quarterly Results (unaudited)

12. Quarterly Results (unaudited)

	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 applicable to common stockholders—basic and diluted	$	(0.70	)	$	(0.95	)	$	(0.96	)	$	(0.99	)


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2015			2015			2015			2015
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	—		$	—		$	—		$	—
Operating expenses	$	10,896		$	10,889		$	19,678		$	20,050
Loss from operations	$	(10,896	)	$	(10,889	)	$	(19,678	)	$	(20,050	)
Other income (expense), net	$	201		$	200		$	203		$	193
Net loss	$	(10,695	)	$	(10,689	)	$	(19,475	)	$	(19,857	)
Net loss per share applicable to common stockholders—basic and diluted	$	(0.53	)	$	(0.40	)	$	(0.68	)	$	(0.66	)

Subsequent Event	12 Months Ended
Subsequent Event	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Event	13. Subsequent Event In February 2017, the Company entered into a Research and License Agreement, the Agreement, with Janssen Pharmaceutica NV, one of the Janssen Pharmaceutical Companies of Johnson and Johnson, Janssen, 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, as well as develop and commercialize JNJ5169, a preclinical compound in development as an oral treatment for IBD. Under the terms of the Agreement, the Company will pay an upfront payment of $1.0 million to Janssen within 30 days of execution of the Agreement. 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. In connection with its entry into the Agreement, in February, 2017, 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 Warrants and the shares issuable upon exercise of the Warrants will be sold and issued without registration under the Securities Act of 1933, the Securities Act.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Basis of Presentation

Recent Accounting Pronouncements

Segment Information

Use of Estimates

Cash and Cash Equivalents

Investments

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.

Income Taxes

Stock-Based Compensation

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, 2016 and 2015.

	Useful Life	December 31, 2016			December 31, 2015
		(in thousands)
Computer equipment and software	3	$	476		$	300
Furniture and fixtures	5		729			243
Equipment	7		50			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		1,763			70
Office equipment under capital lease	3		36			24
			3,054			687
Less accumulated depreciation			(442	)		(147	)
Net property and equipment		$	2,612		$	540

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Accounting Policies [Abstract]

Summary of Equipment and Related Accumulated Depreciation

The following is the summary of property and equipment and related accumulated depreciation as of December 31, 2016 and 2015.

	Useful Life	December 31, 2016			December 31, 2015
		(in thousands)
Computer equipment and software	3	$	476		$	300
Furniture and fixtures	5		729			243
Equipment	7		50			50
Leasehold improvements	Shorter of the useful life or remaining lease term (10 years)		1,763			70
Office equipment under capital lease	3		36			24
			3,054			687
Less accumulated depreciation			(442	)		(147	)
Net property and equipment		$	2,612		$	540

Available for Sale Securities (Tables)

12 Months Ended

Dec. 31, 2016

Investments Debt And Equity Securities [Abstract]

Summary of Available for Sale Securities at Fair Value

Available for sale securities at December 31, 2016 and 2015 consist of the following:

			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

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2015
Cash and cash equivalents	$	49,778	$	—	$	—		$	49,778
Available for sale securities:
Certificates of deposit	$	21,505	—			—		$	21,505
U.S. Government debt securities		46,461	—			(185	)		46,276
Corporate debt securities		20,944		1		(50	)		20,895
Total available for sale securities	$	88,910	$	1	$	(235	)	$	88,676
Total cash, cash equivalents, and available for sale securities	$	138,688	$	1	$	(235	)	$	138,454

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, 2016, by contractual maturity, is as follows:

Due in one year or less	$	65,071
Due after one year		7,937
Total available for sale securities	$	73,008

- 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, 2016

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 December31, 2016 are summarized below:

	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

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2015 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
December 31, 2015
Assets:
Cash and cash equivalents	$	49,778	$	—	$	—	$	49,778
Certificates of deposit		—		21,505		—		21,505
U.S. Government debt securities		—		46,276		—		46,276
Corporate debt securities		—		20,895		—		20,895
	$	49,778	$	88,676	$	—	$	138,454

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2016

Payables And Accruals [Abstract]

Components of Accrued Expenses

Accrued expenses are as follows:


	December 31, 2016		December 31, 2015
	(in thousands)
Accrued clinical	$	23,643	$	4,536
Accrued bonus		2,995		2,178
Accrued payroll		596		518
Professional fees		539		647
Accrued vacation		513		310
Accrued severance		29	—
Other		1,946		1,366
Total accrued expenses	$	30,261	$	9,555

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2016

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, 2016		December 31, 2015
Common stock options and RSU's outstanding		3,579,694		2,231,057
Shares available for issuance under the 2014 Plan ⁽¹⁾		885,328		1,318,732
Shares available for issuance under the ESPP ⁽²⁾		803,105		440,304
Total		5,268,127		3,990,093

⁽¹⁾

⁽²⁾

On February 28, 2017 and February 28, 2016, the shares reserved for future issuance under the ESPP increased by 388,296 and 379,430 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,
	2016		2015		2014
Risk-free interest rate	1.16% - 2.03%		1.44% - 1.95%		1.63% - 2.06%
Dividend yield		0.00%		0.00%		0.00%
Volatility	64.78% - 82.40%		62.47% - 81.25%		67.97% - 77.00%
Expected term (years)	5.51 - 6.25		5.51 - 6.25		6.25

Schedule of Stock Option Activity

The following table summarizes the Company’s stock option activity:

	Shares			Weighted-Average Exercise Price		Weighted-Average Contractual Life (in years)		Aggregate Intrinsic Value
Outstanding, December 31, 2015		2,206,635		$	9.04			$	13,114,811
Granted		1,416,775		$	8.11
Exercised		(86,625	)	$	1.43			$	623,686
Forfeited		(388,779	)	$	8.24			$	267,459
Expired/cancelled		—
Outstanding, December 31, 2016		3,148,006		$	8.93		8.06	$	10,437,947
Options exercisable, December 31, 2016		1,134,870		$	8.34		6.64	$	5,785,199
Expected to vest, December 31, 2016		2,805,675		$	9.31		8.27	$	8,759,055

Schedule of Restricted Stock Activity

A summary of the Company’s restricted stock activity is as follows:

	Shares			Weighted-Average Grant Date Fair Value
Restricted shares as of December 31, 2015		216,716		$	7.80
Granted		—
Vested		(108,688	)	$	7.71
Forfeited		(15,056	)	$	7.42
Restricted shares as of December 31, 2016		92,972		$	8.08

Compensation Cost Related to Share-Based Awards

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

	Years ended December 31,
	2016		2015		2014
	(in thousands)
Research and development	$	2,136	$	2,079	$	2,766
General and administrative		3,689		2,635		3,244
Total	$	5,825	$	4,714	$	6,010

Schedule of Compensation Expense by Type of Award

Compensation expense by type of award:

	Years ended December 31,
	2016		2015		2014
	(in thousands)
Stock options	$	4,674	$	3,660	$	1,925
Restricted stock		266		909		4,085
Restricted stock units		780		62		—
Employee stock purchase plan		105		83		—
Total	$	5,825	$	4,714	$	6,010

Restricted Stock Units

Schedule of Restricted Stock Activity

	Shares			Weighted-Average Grant Date Fair Value
Unvested balance, December 31, 2015		24,425		$	11.15
Granted		450,838		$	7.83
Vested		—
Forfeited		(43,575	)	$	8.38
Outstanding, December 31, 2016		431,688		$	7.96

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

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,
	2016			2015			2014
Federal tax at statutory rate		34.0	%		34.0	%		34.0	%
State and local tax at statutory rate		1.4			3.0			5.5
Research and development tax credits		6.4			0.4			(0.6	)
Equity compensation		(0.2	)		(0.6	)		(1.6	)
Other permanent differences and credits		—			—			(0.1	)
Change in valuation allowance		(41.6	)		(36.8	)		(37.2	)
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,
		2016			2015
	(in thousands)
Deferred tax assets:
Accrued expenses		$	2,170		$	912
Deferred revenue			12,157			—
Intangible assets			449			527
Restricted stock			45			301
Fixed assets			—			—
Non-qualified stock options			2,963			1,558
Research and development credits			10,510			1,829
Net operating loss carryforward			84,372			51,356
Other			326			64
Total deferred tax assets			112,992			56,547
Less valuation allowance			(112,986	)		(56,545	)
Total deferred tax assets, net of valuation allowance			6			2
Deferred tax liabilities:
Fixed assets			(6	)		(2	)
Total deferred tax liabilities			(6	)		(2	)
Net deferred tax asset		$	—		$	—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2016

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Required Under Leases

At December 31, 2016, the Company’s future minimum payments required under these leases are as follows:

			Lease Payments
	Operating		to be Received		Net Operating		Capital
	Lease		from Sublease		Lease Payments		Lease		Total
	(in thousands)
2017	$	3,545	$	257	$	3,288	$	9	$	3,297
2018		3,545		257	$	3,288		5	$	3,293
2019		3,545		—	$	3,545		—	$	3,545
2020		3,545		—	$	3,545		—	$	3,545
2021		3,510		—	$	3,510		—	$	3,510
Thereafter		14,666		—	$	14,666		—	$	14,666
Total	$	32,356	$	514	$	31,842		14	$	31,856
Less amount representing interest								—
Present value of minimum lease payments at December 31, 2016							$	14

- Definition

Tabular disclosure of a lessee's leasing arrangements including: (1) the basis on which contingent rental payments are determined, (2) the existence and terms of renewal or purchase options and escalation clauses, (3) restrictions imposed by lease arrangements, such as those concerning dividends, additional debt, and further leasing, (4) rent holidays, rent concessions, or leasehold improvement incentives and unusual provisions or conditions. Disclosure may also include the specific period used to amortize material leasehold improvements made at the inception of the lease or during the lease term. Additionally, for operating leases having initial or remaining noncancelable lease terms in excess of one year: (a) future minimum rental payments required as of the date of the latest balance sheet presented, in the aggregate and for each of the five succeeding fiscal years, (b) the total of minimum rentals to be received in the future under noncancelable subleases as of the date of the latest balance sheet presented, and (c) for all operating leases, rental expense for each period for which an income statement is presented, with separate amounts for minimum rentals, contingent rentals, and sublease rentals. Rental payments under leases with terms of a month or less that were not renewed need not be included.

+ References + Details

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2016

Earnings Per Share [Abstract]

Calculation of Basic and Diluted Net Loss per Share

The following table presents the calculation of basic and diluted net loss per share applicable to common stockholders:

	Year ended December 31,
	2016			2015			2014
	(in thousands, except share and per share data)
Numerator:
Net loss	$	(135,747	)	$	(60,716	)	$	(37,034	)
Accretion on preferred stock		—			—			(86,899	)
Net loss applicable to common stockholders	$	(135,747	)	$	(60,716	)	$	(123,933	)

Denominator:
Weighted-average number of common shares – basic and diluted		37,716,949			26,469,170			15,406,386
Net loss per share applicable to common stockholders – basic and diluted	$	(3.60	)	$	(2.29	)	$	(8.04	)

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,
	2016		2015		2014
Outstanding stock options		3,148,006		2,206,635		1,526,346
Unvested restricted stock		92,972		216,716		422,145
Unvested restricted stock units		431,688		24,425		—
Total		3,672,666		2,447,776		1,948,491

Quarterly Results (unaudited) (Tables)

12 Months Ended

Dec. 31, 2016

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Results

	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 applicable to common stockholders—basic and diluted	$	(0.70	)	$	(0.95	)	$	(0.96	)	$	(0.99	)


	Three Months Ended
	March 31,			June 30,			September 30,			December 31,
	2015			2015			2015			2015
	(in thousands, except per share data)
	(unaudited)
Collaboration revenue	$	—		$	—		$	—		$	—
Operating expenses	$	10,896		$	10,889		$	19,678		$	20,050
Loss from operations	$	(10,896	)	$	(10,889	)	$	(19,678	)	$	(20,050	)
Other income (expense), net	$	201		$	200		$	203		$	193
Net loss	$	(10,695	)	$	(10,689	)	$	(19,475	)	$	(19,857	)
Net loss per share applicable to common stockholders—basic and diluted	$	(0.53	)	$	(0.40	)	$	(0.68	)	$	(0.66	)

Nature of Organization and Operations - Additional Information (Details)		1 Months Ended						12 Months Ended
	Mar. 06, 2014	Mar. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2016 USD ($)	May 31, 2016 USD ($) shares	Jan. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) Patient Underwritten_offering $ / Patient shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 shares
Nature Of Organization And Operations [Line Items]
Cash and cash equivalents and available for sale securities				$ 260,343,000			$ 138,454,000	$ 260,343,000	$ 138,454,000
Number of months for operating plan sufficiently funded by cash resources								12 months
Stock split, conversion ratio	1.75
Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue								$ 125,000,000
Otsuka Pharmaceutical Company Limited \| Scenario Forecast
Nature Of Organization And Operations [Line Items]
Milestone revenue		$ 33,800,000
Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares \| shares								7,865,293	10,083,070	6,762,000
IPO
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of initial public offering								$ 254,100,000
Number of underwritten public offerings \| Underwritten_offering								5
Follow-on public offering
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of initial public offering						$ 61,000,000
Sale of stock, price per share \| $ / shares						$ 9.00
Follow-on public offering \| Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of initial public offering					$ 5,700,000
Follow-on public offering \| Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares \| shares						7,250,000
Follow-on public offering \| Common Stock \| Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Issuance of common stock, net of issuance costs, shares \| shares					615,293
PRO2TECT and INNO2VATE
Nature Of Organization And Operations [Line Items]
Number of patients \| Patient								5,700
PRO2TECT and INNO2VATE \| Minimum
Nature Of Organization And Operations [Line Items]
Cost of program per patient \| $ / Patient								80,000
PRO2TECT and INNO2VATE \| Maximum
Nature Of Organization And Operations [Line Items]
Cost of program per patient \| $ / Patient								85,000
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 Mitsubishi Tanabe Pharma Corporation, or MTPC, to develop and commercialize vadadustat in Japan and certain other countries in Asia for total payments of up to $350.0 million to fund the vadadustat Phase 3 program, including up to $100.0 million in upfront and development payments, of which $40.0 million was received in January 2016. To the extent Japanese patients are included in the Phase 3 Program, MTPC will fund up to an additional $60.0 million of development costs. If Japanese patients are not included in the Phase 3 Program, MTPC will be responsible for the costs of the local Phase 3 study in Japan and will make no additional funding payments for the Phase 3 Program, and $20.0 million of the $40.0 million the Company received in 2016 would be used to fund local development of vadadustat in Japan or be refunded to MTPC, at MTPC’s discretion.
Development and Commercialize Collaboration Agreement \| Mitsubishi Tanabe Pharma Corporation \| Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue						$ 40,000,000
Milestone revenue refundable				20,000,000				$ 20,000,000
Development and Commercialize Collaboration Agreement \| Maximum \| Mitsubishi Tanabe Pharma Corporation
Nature Of Organization And Operations [Line Items]
Milestone revenue							350,000,000	350,000,000
Additional milestone payments development costs fund							60,000,000
Development and Commercialize Collaboration Agreement \| Maximum \| Mitsubishi Tanabe Pharma Corporation \| Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue							$ 100,000,000	100,000,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company Limited
Nature Of Organization And Operations [Line Items]
Milestone revenue								$ 0
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company Limited \| Global Development Plan
Nature Of Organization And Operations [Line Items]
Reimbursement for Otsuka's share of costs previously incurred		33,800,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company Limited \| Scenario Forecast \| Global Development Plan
Nature Of Organization And Operations [Line Items]
Reimbursement for Otsuka's share of costs previously incurred		$ 33,800,000
Development and Commercialize Collaboration and License Agreement \| Otsuka Pharmaceutical Company Limited \| Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue				125,000,000
Development and Commercialize Collaboration and License Agreement \| Minimum \| Otsuka Pharmaceutical Company Limited \| Global Development Plan
Nature Of Organization And Operations [Line Items]
Additional milestone payments development costs fund				106,200,000
Development and Commercialize Collaboration and License Agreement \| Maximum \| Otsuka Pharmaceutical Company Limited \| Potential Development and Commercialization Milestones
Nature Of Organization And Operations [Line Items]
Milestone revenue				$ 765,000,000
Development and Commercialize Research and License Agreement \| Janssen Pharmaceutica NV
Nature Of Organization And Operations [Line Items]
Research and license agreement terms								Under the terms of the Agreement, Janssen granted us a license for a three-year research term to conduct research on the HIF compound portfolio, unless we elect to extend such research term for up to two additional one-year periods upon payment of an extension fee. During the research term, we may designate one or more compounds as candidates for development and commercialization. Once a compound is designated for development and commercialization, we will be solely responsible for the development and commercialization of the compound worldwide at our own cost and expense
Development and Commercialize Research and License Agreement \| Janssen Pharmaceutica NV \| Subsequent Event
Nature Of Organization And Operations [Line Items]
Research term of license			3 years
Additional period of research			1 year
Upfront payment payable			$ 1,000,000
Due date for payment of upfront payment payable			30 days
Aggregate specified development milestone payments payable			$ 16,500,000
Specified commercial milestones as well as tiered, escalating royalties payable			$ 215,000,000
Development and Commercialize Research and License Agreement \| Maximum \| Janssen Pharmaceutica NV \| Subsequent Event
Nature Of Organization And Operations [Line Items]
Number of extension in research term			2

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Significant uncertain tax positions	$ 0	$ 0
Expected dividend yield	0.00%
Depreciation expense	$ 295,000	$ 96,000	$ 49,000
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

Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 3,054	$ 687
Less accumulated depreciation	(442)	(147)
Net property and equipment	$ 2,612	540
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 476	300
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	$ 729	243
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	$ 50	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	$ 1,763	70
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	$ 24

Available for Sale Securities - Summary of Available for Sale Securities at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 73,048	$ 88,910
Gross Unrealized Gains		1
Gross Unrealized Losses	(40)	(235)
Fair Value	73,008	88,676
Cash and cash equivalents	187,335	49,778	$ 32,780	$ 21,215
Cash and cash equivalents, fair value	187,335	49,778
Total cash, cash equivalents, and available for sale securities - Amortized Cost	260,383	138,688
Cash and cash equivalents and available for sale securities	260,343	138,454
U.S. Government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	50,952	46,461
Gross Unrealized Losses	(32)	(185)
Fair Value	50,920	46,276
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	12,698	21,505
Fair Value	12,698	21,505
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	9,398	20,944
Gross Unrealized Gains		1
Gross Unrealized Losses	(8)	(50)
Fair Value	$ 9,390	$ 20,895

Available for Sale Securities - Estimated Fair Value of Available for Sale Securities by Contractual Maturity (Details) $ in Thousands	Dec. 31, 2016 USD ($)
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 65,071
Due after one year	7,937
Total available for sale securities	$ 73,008

Fair Value of Financial Instruments - Assets Measured or Disclosed at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
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	260,343,000	138,454,000
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	50,920,000	46,276,000
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	187,335,000	49,778,000
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	73,008,000	88,676,000
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	50,920,000	46,276,000
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	187,335,000	49,778,000
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	187,335,000	49,778,000
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	12,698,000	21,505,000
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	12,698,000	21,505,000
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	9,390,000	20,895,000
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	$ 9,390,000	$ 20,895,000

Fair Value of Financial Instruments - Additional Information (Detail) - Level 3 - USD ($)	Dec. 31, 2016	Dec. 31, 2015
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, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued clinical	$ 23,643	$ 4,536
Accrued bonus	2,995	2,178
Accrued payroll	596	518
Professional fees	539	647
Accrued vacation	513	310
Accrued severance	29
Other	1,946	1,366
Total accrued expenses	$ 30,261	$ 9,555

Accrued Expenses - Additional Information (Details)	12 Months Ended
Accrued Expenses - Additional Information (Details)	Dec. 31, 2016 USD ($) Employee
Accrued Expenses [Line Items]
Accrued severance	$ 29,000
Separation Agreement
Accrued Expenses [Line Items]
Severance expense	500,000
Payment out of severance accrual	400,000
Accrued severance	$ 29,000
Number of employees \| Employee	3
Severance agreement description	During 2016, the Company entered into separation agreements with three employees. During 2016, the Company recorded severance expense in the amount of $0.5 million, of which $0.2 million was recorded to general and administrative expense and $0.3 million was recorded to research and development expense. During the year ended December 31, 2016, approximately $0.4 million was paid out of the severance accrual. At December 31, 2016, approximately $29,000 remained in accrued expense in relation to the unpaid severance costs.
Separation Agreement \| General and Administrative Expense
Accrued Expenses [Line Items]
Severance expense	$ 200,000
Separation Agreement \| Research and Development Expense
Accrued Expenses [Line Items]
Severance expense	$ 300,000

Stockholders' Equity - Additional Information (Details)				1 Months Ended	12 Months Ended
Stockholders' Equity - Additional Information (Details)	Feb. 22, 2016 shares	Mar. 06, 2014	Dec. 23, 2013 USD ($) $ / shares shares	May 31, 2016 shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Mar. 25, 2014 shares	Feb. 28, 2014 shares
Class of Stock [Line Items]
Common stock, shares authorized					175,000,000	175,000,000	175,000,000
Common stock, par value \| $ / shares					$ 0.00001	$ 0.00001	$ 0.00001
Common stock, shares issued					38,615,709	30,662,218
Common stock, shares outstanding					38,615,709	30,662,218
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
Common stock, shares reserved for future issuance					5,268,127	3,990,093
Granted, Shares					1,416,775
Stock-based compensation expense \| $					$ 5,825,000	$ 4,714,000	$ 6,010,000
Employee Severance
Class of Stock [Line Items]
Stock-based compensation expense \| $							1,000,000
Restricted Stock Units
Class of Stock [Line Items]
Granted shares of restricted stock	382,338				450,838
Vesting periods					3 years
Stock-based compensation expense \| $					$ 780,000	62,000
Weighted average period of recognition for unrecognized compensation costs					2 years 1 month 10 days
Granted, Weighted-Average Grant Date Fair Value \| $ / shares					$ 7.83
Unrecognized compensation cost \| $					$ 2,000,000
Total compensation cost to be recognized \| $					$ 2,900,000
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	624,275
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 or 12 equal quarterly installments beginning in the thirteenth month 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 \| $					$ 4,674,000	3,660,000	1,925,000
Stock Options \| Minimum
Class of Stock [Line Items]
Vesting periods					12 months
Stock Options \| Maximum
Class of Stock [Line Items]
Vesting periods					48 months
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 \| $					$ 266,000	$ 909,000	$ 4,085,000
Weighted average period of recognition for unrecognized compensation costs					6 months 22 days
Granted, Weighted-Average Grant Date Fair Value \| $ / shares			$ 7.42
Restricted stock requisite service period description					The awards of restricted stock contained a performance condition wherein vesting is 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 have a requisite service period that was complete upon grant. The remainder of the awards of restricted stock have a requisite service period of four years whereby the award vests 25% on the one year anniversary of the 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 \| $					$ 48,000
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 \| $					$ 3,000
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance					885,328	1,318,732			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					1,304,275
2014 Plans \| Director
Class of Stock [Line Items]
Granted, Shares					112,500
2014 Plans \| Inducement Award Program
Class of Stock [Line Items]
Common stock, shares reserved for future issuance				350,000
Granted, Shares				255,000
Compensation not yet recognized, stock options \| $					$ 9,600,000
Weighted average period of recognition for unrecognized compensation costs					2 years 5 months 16 days
2014 Plans \| Inducement Award Program \| Employees
Class of Stock [Line Items]
Granted, Shares					255,000
2014 Plans \| Restricted Stock Units \| Employees
Class of Stock [Line Items]
Granted shares of restricted stock					450,838
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					16,629
Stock-based compensation expense \| $					$ 100,000

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	5,268,127	3,990,093
Stock Options and Restricted Stock Units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	3,579,694	2,231,057
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	885,328	1,318,732	1,785,000
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	803,105	440,304

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Parenthetical) (Details) - shares	Feb. 28, 2017	Jan. 01, 2017	Feb. 28, 2016	Jan. 01, 2016
2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance				986,800
Subsequent Event \| 2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance		1,265,863
Employee Stock Purchase Plan
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance			379,430
Employee Stock Purchase Plan \| Subsequent Event
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance	388,296

Stockholders' Equity - Schedule of Assumptions Used in Black-Scholes Option Pricing Model (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
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%
Expected term (years)			6 years 3 months
Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.16%	1.44%	1.63%
Volatility	64.78%	62.47%	67.97%
Expected term (years)	5 years 6 months 4 days	5 years 6 months 4 days
Stock Options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.03%	1.95%	2.06%
Volatility	82.40%	81.25%	77.00%
Expected term (years)	6 years 3 months	6 years 3 months

Stockholders' Equity - Schedule of Stock Option Activity (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares
Share under option
Outstanding beginning balance, Shares \| shares	2,206,635
Granted, Shares \| shares	1,416,775
Exercised, Shares \| shares	(86,625)
Forfeited, Shares \| shares	(388,779)
Outstanding ending balance, Shares \| shares	3,148,006
Options exercisable at end of period, Shares \| shares	1,134,870
Expected to vest at end of period, Shares \| shares	2,805,675
Weighted Average-Exercise Price
Outstanding beginning balance, Weighted-Average Exercise Price \| $ / shares	$ 9.04
Granted, Weighted-Average Exercise Price \| $ / shares	8.11
Exercised, Weighted-Average Exercise Price \| $ / shares	1.43
Forfeited, Weighted-Average Exercise Price \| $ / shares	8.24
Outstanding ending balance, Weighted-Average Exercise Price \| $ / shares	8.93
Options exercisable at end of period, Weighted-Average Exercise Price \| $ / shares	8.34
Expected to vest at end of period, Weighted-Average Exercise Price \| $ / shares	$ 9.31
Weighted-Average Remaining Contractual Term
Outstanding ending balance, Weighted-Average Contractual Life(in years)	8 years 22 days
Options exercisable at end of period, Weighted-Average Contractual Life(in years)	6 years 7 months 21 days
Expected to vest at end of period, Weighted-Average Contractual Life(in years)	8 years 3 months 7 days
Aggregate Intrinsic Value
Outstanding beginning balance, Aggregate Intrinsic Value \| $	$ 13,114,811
Exercised, Aggregate Intrinsic Value \| $	623,686
Forfeited, Aggregate Intrinsic Value \| $	267,459
Outstanding ending balance, Aggregate Intrinsic Value \| $	10,437,947
Options exercisable at end of period, Aggregate Intrinsic Value \| $	5,785,199
Expected to vest at end of period, Aggregate Intrinsic Value \| $	$ 8,759,055

Stockholders' Equity - Summary of Company Restricted Stock Activity (Details) - $ / shares			12 Months Ended
	Feb. 22, 2016	Dec. 23, 2013	Dec. 31, 2016
Restricted Stock
Restricted stock activity, Shares
Restricted shares, Unvested beginning balance, Shares			216,716
Vested, Shares			(108,688)
Forfeited, Shares			(15,056)
Restricted shares, Unvested ending balance, Shares			92,972
Restricted shares, Unvested beginning balance, Weighted-Average Grant Date Fair Value			$ 7.80
Granted, Weighted-Average Grant Date Fair Value		$ 7.42
Vested, Weighted-Average Grant Date Fair Value			7.71
Forfeited, Weighted-Average Grant Date Fair Value			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			24,425
Granted, Shares	382,338		450,838
Forfeited, Shares			(43,575)
Restricted shares, Unvested ending balance, Shares			431,688
Restricted shares, Unvested beginning balance, Weighted-Average Grant Date Fair Value			$ 11.15
Granted, Weighted-Average Grant Date Fair Value			7.83
Forfeited, Weighted-Average Grant Date Fair Value			8.38
Restricted shares, Unvested ending balance, Weighted-Average Grant Date Fair Value			$ 7.96

Stockholders Equity - Compensation Cost Related to Share-Based Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,825	$ 4,714	$ 6,010
Research and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	2,136	2,079	2,766
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 3,689	$ 2,635	$ 3,244

Stockholders Equity - Schedule of Compensation Expense by Type of Award (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 5,825	$ 4,714	$ 6,010
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	4,674	3,660	1,925
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	266	909	$ 4,085
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	780	62
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 105	$ 83

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Line Items]
Current income tax expense or benefit	$ 0	$ 0	$ 0
Deferred income tax expense or benefit	0	0	0
Increase in valuation allowance, deferred tax assets	56,400,000	22,300,000
Deferred capitalized start up expense net of amortization	900,000	1,000,000
Deferred income tax amortization	$ 1,000,000	900,000
NOL and R&D tax credit carry forward expiration year	2036
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
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 234,500,000	140,500,000
Operating Loss Carryforwards Expiration Year	2036
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 103,900,000	$ 111,900,000
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	2013
Federal and State \| Latest Tax Year
Income Tax Disclosure [Line Items]
Tax years remain open and subject to examination	2015
Federal and State \| Research and Development
Income Tax Disclosure [Line Items]
Tax credit carryforwards	$ 10,800,000

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, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Federal tax at statutory rate	34.00%	34.00%	34.00%
State and local tax at statutory rate	1.40%	3.00%	5.50%
Research and development tax credits	6.40%	0.40%	(0.60%)
Equity compensation	(0.20%)	(0.60%)	(1.60%)
Other permanent differences and credits			(0.10%)
Change in valuation allowance	(41.60%)	(36.80%)	(37.20%)
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, 2016	Dec. 31, 2015
Deferred tax assets:
Accrued expenses	$ 2,170	$ 912
Deferred revenue	12,157
Intangible assets	449	527
Restricted stock	45	301
Non-qualified stock options	2,963	1,558
Research and development credits	10,510	1,829
Net operating loss carryforward	84,372	51,356
Other	326	64
Total deferred tax assets	112,992	56,547
Less valuation allowance	(112,986)	(56,545)
Total deferred tax assets, net of valuation allowance	6	2
Deferred tax liabilities:
Fixed assets	(6)	(2)
Total deferred tax liabilities	(6)	(2)
Net deferred tax asset	$ 0	$ 0

Commitments and Contingencies - Additional Information (Details)		12 Months Ended
	Feb. 21, 2017	Dec. 31, 2016 USD ($) ft² Extension_Option	Dec. 31, 2015 USD ($)	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		$ 256,765
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		$ 514,000
Term for security deposit from execution of sublease		30 days
Rent expense associated with lease		$ 2,500,000	$ 900,000
Contract cost incurred in research and development activities		24,900,000
Total remaining contract costs		$ 406,400,000
Subsequent Event
Commitments And Contingencies [Line Items]
Plaintiff period of appeal	30 days
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 period, number of extension options \| Extension_Option		1
Lease extension period		2 years
Lease period		5 years
Office Equipment One
Commitments And Contingencies [Line Items]
Capital leases term		3 years
Capital lease commencement period		2014-02
Office Equipment Two
Commitments And Contingencies [Line Items]
Capital leases term		3 years
Capital lease commencement period		2015-04
Office Equipment Three
Commitments And Contingencies [Line Items]
Capital leases term		3 years
Capital lease commencement period		2016-02
Other Assets
Commitments And Contingencies [Line Items]
Total security deposit in connection with lease		$ 1,280,857	$ 1,280,857
Other Liabilities
Commitments And Contingencies [Line Items]
Total security deposit liability in connection with sublease		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, 2016 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2017	$ 3,545
Operating Lease, 2018	3,545
Operating Lease, 2019	3,545
Operating Lease, 2020	3,545
Operating Lease, 2021	3,510
Operating Lease, Thereafter	14,666
Operating Lease, Total	32,356
Lease Payments to be Received from Sublease, 2017	257
Lease Payments to be Received from Sublease, 2018	257
Lease Payments to be Received from Sublease, Total	514
Net Operating Lease Payments, 2017	3,288
Net Operating Lease Payments, 2018	3,288
Net Operating Lease Payments, 2019	3,545
Net Operating Lease Payments, 2020	3,545
Net Operating Lease Payments, 2021	3,510
Net Operating Lease Payments, Thereafter	14,666
Net Operating Lease Payments, Total	31,842
Capital Lease, 2017	9
Capital Lease, 2018	5
Capital Lease, Total	14
Capital Lease, Present value of minimum lease payments at December 31, 2016	14
Net Operating Lease Payments and Capital Lease, 2017	3,297
Net Operating Lease Payments and Capital Lease, 2018	3,293
Net Operating Lease Payments and Capital Lease, 2019	3,545
Net Operating Lease Payments and Capital Lease, 2020	3,545
Net Operating Lease Payments and Capital Lease, 2021	3,510
Net Operating Lease Payments and Capital Lease, Thereafter	14,666
Net Operating Lease Payments and Capital Lease, Total	$ 31,856

Significant Agreements - Additional Information (Details)		1 Months Ended				3 Months Ended	12 Months Ended
	Jan. 02, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) AccountingUnit
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, noncurrent			$ 115,321,000			$ 115,321,000	$ 115,321,000
Number of accounting units \| AccountingUnit							3
Cost share payment received							$ 33,800,000
Allocated arrangement consideration							265,000,000
Recognized revenue under license agreement						1,535,000	1,535,000
Deferred revenue			157,300,000			157,300,000	157,300,000
Unbilled receivable			33,800,000			33,800,000	33,800,000
Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated cost share payment receivable	$ 106,200,000
Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							125,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Additional milestone payments to be received as development costs							$ 0
Collaboration Agreement, expiration period							10 years
Collaboration Agreement, notice period for termination							12 months
Deferred revenue, noncurrent				$ 40,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue					$ 350,000,000		$ 350,000,000
Additional milestone payments to be received as development costs							60,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue				$ 40,000,000
Milestone revenue refundable			20,000,000			$ 20,000,000	20,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Upfront \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue					$ 100,000,000		100,000,000
Mitsubishi Tanabe Pharma Corporation \| Development and Commercialize Collaboration Agreement \| Additional Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							250,000,000
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 \| Approval Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							65,000,000
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
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize Collaboration and License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							$ 0
Percentage of market penetration for license agreement							90.00%
License agreement, notice period for termination							12 months
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize 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 Collaboration and License Agreement \| Minimum \| Subsequent Event \| Global Development Plan
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fund	$ 106,200,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize Collaboration and License Agreement \| Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue			$ 125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize Collaboration and License Agreement \| Development Milestones \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							$ 125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize Collaboration and License Agreement \| Up-front, Non-refundable and Non-creditable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							125,000,000
Otsuka Pharmaceutical Company. Ltd. \| Development and Commercialize 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 Collaboration and License Agreement \| Commercial Milestone Payments \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue							$ 575,000,000

Net Loss per Share - Calculation of Basic and Diluted Net Loss per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net loss	$ (37,862)	$ (36,308)	$ (35,779)	$ (25,798)	$ (19,857)	$ (19,475)	$ (10,689)	$ (10,695)	$ (135,747)	$ (60,716)	$ (37,034)
Accretion on preferred stock											(86,899)
Net loss applicable to common stockholders - basic and diluted									$ (135,747)	$ (60,716)	$ (123,933)
Denominator:
Weighted-average number of common shares – basic and diluted									37,716,949	26,469,170	15,406,386
Net loss per share applicable to common stockholders - basic and diluted	$ (0.99)	$ (0.96)	$ (0.95)	$ (0.70)	$ (0.66)	$ (0.68)	$ (0.40)	$ (0.53)	$ (3.60)	$ (2.29)	$ (8.04)

Net Loss per Share - Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,672,666	2,447,776	1,948,491
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	3,148,006	2,206,635	1,526,346
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	422,145
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	431,688	24,425

Quarterly Results (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue	$ 1,535								$ 1,535
Operating expenses	39,579	$ 36,182	$ 36,188	$ 26,046	$ 20,050	$ 19,678	$ 10,889	$ 10,896	137,995	$ 61,513	$ 37,940
Loss from operations	(38,044)	(36,182)	(36,188)	(26,046)	(20,050)	(19,678)	(10,889)	(10,896)	(136,460)	(61,513)	(37,940)
Other income (expense), net	182	(126)	409	248	193	203	200	201
Net loss	$ (37,862)	$ (36,308)	$ (35,779)	$ (25,798)	$ (19,857)	$ (19,475)	$ (10,689)	$ (10,695)	$ (135,747)	$ (60,716)	$ (37,034)
Net loss per share applicable to common stockholders—basic and diluted	$ (0.99)	$ (0.96)	$ (0.95)	$ (0.70)	$ (0.66)	$ (0.68)	$ (0.40)	$ (0.53)	$ (3.60)	$ (2.29)	$ (8.04)

Subsequent Event - Additional Information (Details) - USD ($)	1 Months Ended
	Feb. 28, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Common stock, shares issued		38,615,709	30,662,218
Subsequent Event \| Janssen Pharmaceutica NV \| Development and Commercialize Research and License Agreement
Subsequent Event [Line Items]
Upfront payment payable	$ 1,000,000
Due date for payment of upfront payment payable	30 days
Aggregate specified development milestone payments payable	$ 16,500,000
Specified commercial milestones as well as tiered, escalating royalties payable	$ 215,000,000
Subsequent Event \| Johnson & Johnson Innovation \| Development and Commercialize Research and License Agreement \| Warrant
Subsequent Event [Line Items]
Common stock, shares issued	509,611
Exercise price	$ 9.81

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