Document and Entity Information	9 Months Ended
Document and Entity Information	Sep. 30, 2015	Nov. 05, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Trading Symbol	AKBA
Entity Registrant Name	Akebia Therapeutics, Inc.
Entity Central Index Key	0001517022
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		30,631,737

Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 66,712	$ 32,780
Available for sale securities	90,754	76,138
Accounts receivable	14	48
Prepaid expenses and other current assets	1,324	1,514
Total current assets	158,804	110,480
Property and equipment, net	479	210
Other assets	305	305
Total assets	159,588	110,995
Current liabilities:
Accounts payable	5,273	2,021
Accrued expenses	8,893	4,864
Total current liabilities	14,166	6,885
Other liabilities	10	32
Total liabilities	14,176	6,917
Commitments and contingencies (Note 9)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized at September 30, 2015 and December 31, 2014; 0 shares issued and outstanding at September 30, 2015 and December 31, 2014
Common stock: $0.00001 par value; 175,000,000 shares authorized at September 30, 2015 and December 31, 2014; 30,218,094 and 20,370,624 shares issued and outstanding at September 30, 2015 and December 31, 2014, respectively	0	0
Additional paid-in capital	287,113	204,969
Treasury stock, at cost, 8,463 shares	(162)	(162)
Accumulated other comprehensive loss	(7)	(56)
Accumulated deficit	(141,532)	(100,673)
Total stockholders' equity	145,412	104,078
Total liabilities and stockholders' equity	$ 159,588	$ 110,995

Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2015	Dec. 31, 2014
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	30,218,094	20,370,624
Common stock, shares outstanding	30,218,094	20,370,624
Treasury Stock, shares	8,463	8,463

Condensed Consolidated Statements of Operations and Comprehensive Loss (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating expenses:
Research and development	$ 15,790	$ 6,648	$ 30,477	$ 18,330
General and administrative	3,888	2,936	10,986	9,003
Total operating expenses	19,678	9,584	41,463	27,333
Operating loss	(19,678)	(9,584)	(41,463)	(27,333)
Other income (expense):
Interest income (expense), net	139	56	350	125
Reimbursements from Aerpio	64	180	254	544
Net loss	(19,475)	(9,348)	(40,859)	(26,664)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(19,475)	(9,348)	(40,859)	(26,664)
Accretion on preferred stock				(86,899)
Net loss applicable to common stockholders	(19,475)	(9,348)	(40,859)	(113,563)
Net loss per share applicable to common stockholders—basic and diluted	$ (0.68)	$ (0.47)	$ (1.62)	$ (8.16)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted	28,784,231	19,691,167	25,175,077	13,920,651
Comprehensive loss:
Net loss	(19,475)	(9,348)	(40,859)	(26,664)
Other comprehensive loss - unrealized loss on securities	20	(43)	(7)	(52)
Comprehensive loss	$ (19,455)	$ (9,391)	$ (40,866)	$ (26,716)

Condensed Consolidated Statements of Cash Flows (USD $)	9 Months Ended
Condensed Consolidated Statements of Cash Flows (USD $)	Sep. 30, 2015	Sep. 30, 2014
Operating activities:
Net loss	$ (40,859,000)	$ (26,664,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	85,000	33,000
Amortization of premium/discount on investments	418,000	124,000
Stock-based compensation expense	3,386,000	5,125,000
Changes in operating assets and liabilities:
Accounts receivable	34,000	78,000
Prepaid expenses and other current assets	190,000	(688,000)
Accounts payable and accrued expenses	7,276,000	3,683,000
Other liabilities	(25,000)	29,000
Net cash used in operating activities	(29,495,000)	(18,280,000)
Investing activities:
Purchase of equipment	(342,000)	(208,000)
Proceeds from maturities of available for sale securities	49,547,000	6,990,000
Purchases of available for sale securities	(64,531,000)	(64,497,000)
Net cash used in investing activities	(15,326,000)	(57,715,000)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	78,579,000	104,293,000
Proceeds from employee stock purchase plan	109,000
Proceeds from the exercise of stock options	70,000
Repurchase of treasury stock		(79,000)
Payments received on promissory notes issued in exchange for shares of common stock		237,000
Payments on capital lease obligations	(5,000)	(3,000)
Net cash provided by financing activities	78,753,000	104,448,000
Increase in cash and cash equivalents	33,932,000	28,453,000
Cash and cash equivalents at beginning of period	32,780,000	21,215,000
Cash and cash equivalents at end of period	66,712,000	49,668,000
Non-cash financing activities:
Accretion of preferred stock to redemption value		86,899,000
Unpaid initial public offering issuance costs		15,000,000
Assets acquired under capital lease	$ 12,000	$ 12,000

Nature of Organization and Operations	9 Months Ended
Nature of Organization and Operations	Sep. 30, 2015
Accounting Policies [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Akebia Therapeutics, Inc. (Akebia, or the Company) is a biopharmaceutical company focused on delivering innovative therapies to patients with kidney disease through the biology of hypoxia-inducible factor, or HIF. HIF is the primary regulator of the production of red blood cells in the body and a potentially novel mechanism of treating anemia. The Company’s lead product candidate, vadadustat, formerly known as AKB-6548, is being developed as a once-daily oral therapy and has successfully completed Phase 2 development demonstrating that vadadustat can safely and predictably raise hemoglobin levels in patients with anemia related to chronic kidney disease. 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, nor is there any assurance of any future product revenue. The Company’s product candidates are subject to long development cycles and there is no assurance the Company will be able to successfully 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, 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 the ability to protect its proprietary technology. If the Company does not successfully commercialize any of its products, it will be unable to generate product revenue or achieve profitability. On March 25, 2014, the Company completed its initial public offering, or IPO, whereby the Company sold 6,762,000 shares of common stock, including 879,647 shares of common stock pursuant to the full exercise of an over-allotment option granted to the underwriters in connection with the offering, at a price of $17.00 per share. The shares began trading on the NASDAQ Global Market on March 20, 2014. The aggregate net proceeds received by the Company from the offering were $104.4 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. Upon the closing of the IPO, all outstanding shares of convertible redeemable preferred stock converted into 12,115,183 shares of common stock. Additionally, the Company is now authorized to issue up to 175,000,000 shares of common stock and 25,000,000 shares of undesignated preferred stock. In April 2015, the Company completed a follow-on public offering whereby the Company sold 8,363,636 shares of common stock, including 1,090,909 share of common stock pursuant to the full exercise of an over-allotment granted to the underwriters in connection with the offering, at a price of $8.25 per share. The aggregate net proceeds received by the Company from the offering were approximately $64.6 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. In August 2015, the Company entered into a Sales Agreement with Cantor Fitzgerald & Co. to periodically sell up to $50 million of shares of the Company’s common stock in “at-the-market” (ATM) offerings. During the third quarter of 2015, the Company sold 1,311,562 shares of common stock pursuant to the Sales Agreement. The aggregate net proceeds received by the Company were approximately $14.2 million, net of commissions. The Company believes that it can continue as a going concern as its cash resources of approximately $157.5 million at September 30, 2015 will be sufficient to allow the Company to fund its current operating plan through at least the next twelve months. There can be no assurance, however, that the current operating plan will be achieved in the timeframe 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. Unless otherwise indicated, all information in these condensed 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. The Company was incorporated on February 27, 2007 under the laws of the State of Delaware.

- Definition

The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.

+ References+ Details

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Conversion of Redeemable Preferred Stock

Upon the closing of the Company’s IPO on March 25, 2014, all outstanding shares of convertible redeemable preferred stock converted into 12,115,183 shares of common stock. The Company’s preferred stock was redeemable at the greater of fair value or the original issuance price. The Company recorded $86.9 million of accretion on the preferred stock in the period from January 1, 2014 through the date of the closing of its IPO which represents the difference in the carrying value at December 31, 2013 and the fair value of the preferred stock just prior to conversion into common stock.

Basis of Presentation

The accompanying condensed 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 United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K (File No. 001-3652), which was filed with the Securities and Exchange Commission (“SEC”) on March 4, 2015.

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.

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 condensed consolidated 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: percent complete for clinical accruals, stock-based compensation expense, fair value of common stock and preferred stock and the Company’s other equity instruments (in periods prior to the IPO), accrued expenses, prepaid expenses and income taxes.

Prior to the IPO, 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 IPO 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 IPO or sale of the Company.

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 September 30, 2015, 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 September 30, 2015. Unrealized losses on available-for-sale securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, 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 (expense), net” within the Condensed Consolidated Statements of Operations and Comprehensive Loss. We also include 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.

Research and Development

Costs incurred in connection with research and development activities are expensed as incurred. Research and development expenses consist of (i) employee-related expenses, including salaries, benefits, travel and stock-based compensation expense; (ii) external research and development expenses incurred under arrangements with third parties, such as contract research organizations, investigational sites and consultants; (iii) the cost of acquiring, developing and manufacturing clinical study materials; (iv) facilities and other expenses, which include direct and allocated expenses for rent and maintenance of facilities; and (v) costs associated with preclinical and clinical activities and regulatory operations.

The Company enters into consulting, research and other agreements with consulting firms, researchers, universities and others for the provision of goods and services. Under such agreements, the Company may pay for services on an hourly, monthly, quarterly, project or other basis. Such arrangements are generally cancellable upon reasonable notice and payment of costs incurred. Costs are considered incurred based on an evaluation of the progress to completion of specific tasks under each contract using information and data provided to us by the Company’s clinical sites and vendors. These costs consist of direct and indirect costs associated with specific projects, as well as fees paid to various entities that perform certain research on behalf of the Company.

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 ASC 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 condensed consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the condensed consolidated 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 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 September 30, 2015 and December 31, 2014, 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 value of its common stock 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 a public market for the trading of the Company’s common stock and a lack of company-specific historical and implied volatility data, 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 either service- or performance-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. Compensation expense related to awards to employees with performance-based vesting conditions is recognized based on the grant date fair value over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable. Consistent with the guidance in ASC 505-50, compensation expense related to awards to non-employees with performance-based vesting conditions is recognized based on the then-current fair value at each financial reporting date prior to the measurement date over the requisite service period using the accelerated attribution method to the extent achievement of the performance condition is probable.

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 5). The carrying amounts of accounts receivable, 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, investments and accounts receivable are the only financial instruments that potentially subject the Company to concentrations of credit risk. At September 30, 2015 and December 31, 2014, all of the Company’s cash was deposited in accounts at two principal financial institutions. 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 September 30, 2015 and December 31, 2014.

	Useful Life	September 30, 2015			December 31, 2014
		(in thousands)
Computer equipment and software	3	$	237		$	99
Furniture and fixtures	5		243			117
Equipment	7		46			6
Leasehold improvements	Shorter of the useful life or remaining lease term (3 years)		64			27
Office equipment under capital lease	3		24			12
			614			261
Less accumulated depreciation			(135	)		(51	)
Net property and equipment		$	479		$	210

Depreciation expense, including expense associated with assets under capital leases, was approximately $35,000 and $13,000 for the three months ended September 30, 2015 and 2014, respectively and $85,000 and $33,000 for the nine months ended September 30, 2015 and 2014, respectively.

- Definition

The entire disclosure for all significant accounting policies of the reporting entity.

+ References+ Details

Available for Sale Securities

9 Months Ended

Sep. 30, 2015

Investments Debt And Equity Securities [Abstract]

Available for Sale Securities

3. Available for sale securities

Available for sale securities at September 30, 2015 and December 31, 2014 consist of the following:

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
September 30, 2015
Cash and cash equivalents:
Cash and money market account	$	66,712	$	—	$	—		$	66,712
Total cash and cash equivalents	$	66,712	$	—	$	—		$	66,712
Available for sale securities:
Certificates of deposit	$	20,170	—		—			$	20,170
U.S. Government debt securities		48,531		15		(6	)		48,540
Corporate debt securities		22,060		5		(21	)		22,044
Total available for sale securities	$	90,761	$	20	$	(27	)	$	90,754
Total cash, cash equivalents, and available for sale securities	$	157,473	$	20	$	(27	)	$	157,466

The estimated fair value of the Company’s available for sale securities balance at September 30, 2015, by contractual maturity, is as follows:

Due in one year or less	$	39,783
Due after one year		50,971
Total available for sale securities	$	90,754

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2014
Cash and cash equivalents:
Cash and money market account	$	32,780	$	—	$	—		$	32,780
Total cash and cash equivalents	$	32,780	$	—	$	—		$	32,780
Available for sale securities:
Certificates of deposit	$	13,429	—			—		$	13,429
U.S. Government debt securities		38,412		1		(28	)		38,385
Commercial paper		2,499		—		—			2,499
Corporate debt securities		21,854		3		(32	)		21,825
Total available for sale securities	$	76,194	$	4	$	(60	)	$	76,138
Total cash, cash equivalents, and available for sale securities	$	108,974	$	4	$	(60	)	$	108,918

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-Glossary Debt Security

-URI http://asc.fasb.org/extlink&oid=6509901

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

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-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

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-Name Accounting Standards Codification

-Topic 942

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-Glossary Equity Security

-URI http://asc.fasb.org/extlink&oid=6511694

+ Details

Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2015

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 marketable securities within Level 1 or Level 2. This is because the Company values its cash equivalents and marketable 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 September 30, 2015 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Cash and cash equivalents	$	66,712	$	—	$	—	$	66,712
Certificates of deposit		—		20,170		—		20,170
U.S. Government debt securities		—		48,540		—		48,540
Corporate debt securities		—		22,044		—		22,044
	$	66,712	$	90,754	$	—	$	157,466

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

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2014 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Cash and cash equivalents	$	32,780	$	—	$	—	$	32,780
Certificates of deposit		—		13,429		—		13,429
U.S. Government debt securities		—		38,385		—		38,385
Commercial paper		—		2,499		—		2,499
Corporate debt securities		—		21,825		—		21,825
	$	32,780	$	76,138	$	—	$	108,918

The Company had no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) at September 30, 2015 and December 31, 2014.

Investment securities are exposed to various risks such as interest rate, market and credit risks. 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

9 Months Ended

Sep. 30, 2015

Payables And Accruals [Abstract]

Accrued Expenses

5. Accrued Expenses

Accrued expenses are as follows:

	September 30,		December 31,
	2015		2014
	(in thousands)
Professional fees	$	5,785	$	2,460
Accrued bonus		1,240		1,286
Accrued vacation		258		177
Accrued severance		29		179
Accrued payroll		582		213
Other		999		549
Total accrued expenses	$	8,893	$	4,864

In August 2014, the Company entered into a separation agreement with an employee. The Company records the expense and liability associated with the separation agreement ratably over the period from August 5, 2014 through December 31, 2015 because the severance payments are subject to continued service and forfeiture until December 31, 2015. During the third quarter of 2015, the Company recorded severance expense in the amount of approximately $73,000, which was recorded to research and development expense. During the first nine months of 2015, approximately $287,000 was paid out of the severance accrual. Payments under this separation agreement will be paid out through December 2015.

Stockholders' Equity

9 Months Ended

Sep. 30, 2015

Equity [Abstract]

Stockholders' Equity

6. Stockholders’ Equity

As of September 30, 2015, the authorized capital stock of the Company included 175,000,000 shares of common stock, par value $0.00001 per share and 25,000,000 shares of undesignated preferred stock, par value $0.00001 per share.

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 condensed consolidated 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.

Reserved for Future Issuance

As of September 30, 2015 and December 31, 2014 based on the authorized shares for each series, the Company has reserved the following shares of common stock for future issuance:

	September 30,		December 31,
	2015		2014
Options to purchase common stock		2,251,908		1,526,346
Shares available for future issuance		1,342,719		1,549,154
Total		3,594,627		3,075,500

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section C

Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-Name Staff Accounting Bulletin (SAB)

-Number Topic 4

-Section E

Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(d),(e))

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-Name Accounting Standards Codification

-Topic 505

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-Paragraph 4

-Subparagraph (SAB TOPIC 4.C)

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-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.29-31)

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

-Glossary Preferred Stock

-URI http://asc.fasb.org/extlink&oid=6521494

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-Topic 505

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-Paragraph 2

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-Topic 505

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-Paragraph 4

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-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 4.E)

-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

+ Details

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	7. Income Taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. There were no significant income tax provisions or benefits for the three and nine months ended September 30, 2015 and 2014. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References+ Details

Commitments and Contingencies

9 Months Ended

Sep. 30, 2015

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. Commitments and Contingencies

In December 2013, the Company entered into a three-year lease for 6,837 square feet of office space in Cambridge, Massachusetts. The lease has monthly lease payments of approximately $31,000 for the first twelve months, with annual rent escalation thereafter, and provides a rent abatement of approximately $31,000 for the first full calendar month of the lease term. The lease term commenced and rental payments began in January 2014. The Company recorded a deferred lease obligation in 2014 which represents the cumulative difference between actual facility lease payments and lease expense recognized ratably over the lease period, which is included in other liabilities. In accordance with the lease, the Company entered into a cash-collateralized irrevocable standby letter of credit in the amount of $125,345, naming the landlord as beneficiary.

In December 2014, the Company entered into a First Amendment to Lease, or the Amendment, for additional office space contiguous to its current office space in Cambridge, Massachusetts. The Amendment includes leasing an additional 8,530 square feet of office space, or the Expansion Space, with an occupancy date of March 13, 2015. The Amendment provides for additional monthly lease payments of approximately $45,000 for the 8,530 square feet for the first twelve months and provides for annual rent escalations thereafter. The monthly rent on the existing 6,837 square feet will remain at approximately $32,000 through December 31, 2016, the expiration of the lease. The Amendment includes a Landlord’s contribution for leasehold improvements in the amount of approximately $100,000 which will be accounted for as a deferred lease incentive and reduction in monthly rent expense over the term of the lease. The Company recorded an additional deferred lease obligation for the Expansion Space which represents the cumulative difference between actual facility lease payments and lease expense recognized ratably over the lease period. The Company has an existing cash-collateralized irrevocable standby letter of credit of $125,345, naming the landlord as beneficiary. In connection with the Amendment, the Company paid an additional cash security deposit to the landlord of $179,130. These amounts are included in other assets.

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

At September 30, 2015, the Company’s future minimum payments required under these leases are as follows:

	Operating		Capital
	Lease		Lease		Total
	(in thousands)
2015	$	230	$	2	$	232
2016		936		8		944
2017		—		5		5
2018		—		1		1
Total	$	1,166		16	$	1,182
Less amount representing interest				—
Present value of minimum lease payments at September 30, 2015			$	16

The Company recorded approximately $0.2 million and $0.1 million in rent expense for the three months ended September 30, 2015 and 2014, respectively, and approximately $0.6 million and $0.3 million in rent expense for the nine months ended September 30, 2015 and 2014, respectively.

The Company contracts with various organizations to conduct research and development activities with remaining contract costs to the Company of approximately $19.6 million and $4.3 million at September 30, 2015 and December 31, 2014, respectively. The scope of the services under the 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 its 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 our 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 “Securities Act”). 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, we 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 is currently pending. The Company believes such claims are without merit, and will engage in a vigorous defense of such litigation.

The Company is not able to predict the outcome of the lawsuit described above or estimate the amount or range of any possible loss the Company might incur if the Company does not prevail in the final, non-appealable determination of this lawsuit. Therefore, we have not accrued any amounts in connection with this lawsuit.

- Definition

The entire disclosure for commitments and contingencies.

+ References+ Details

Stock-Based Compensation

9 Months Ended

Sep. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

9. Stock-Based Compensation

On February 28, 2014, the Company’s Board of Directors adopted its 2014 Incentive Plan (2014 Plan) and its 2014 Employee Stock Purchase Plan (ESPP), which were subsequently approved by its stockholders and became effective upon the closing of the Company’s IPO on March 25, 2014. The 2014 Plan replaces the 2008 Equity Incentive Plan (2008 Plan).

The 2014 Plan allows for the granting of stock options, stock appreciation rights, or SARs, restricted stock, unrestricted stock, RSUs, performance awards and other awards convertible into or otherwise based on shares of our common stock. Dividend equivalents may also be provided in connection with an award under the 2014 Plan. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2014 Plan. The Company initially reserved 1,785,000 shares of its common stock for the issuance of awards under the 2014 Plan. The 2014 Plan provides that the number of shares reserved and available for issuance under the 2014 Plan will automatically increase annually on January 1^st of each calendar year, by an amount equal to three percent (3%) of the number of shares of stock outstanding on a fully diluted basis as of the close of business on the immediately preceding December 31^st. The 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). Subject to adjustment, no more than 1,131,937 shares of our common stock may be delivered in satisfaction of incentive stock options awarded under the 2014 Plan. Any options or awards outstanding under the 2008 Plan at the time of adoption of the 2014 Plan remain outstanding and effective.

The ESPP authorizes the initial issuance of up to a total of 262,500 shares of the Company’s common stock to participating employees. The first offering period under the ESPP opened on January 2, 2015.

As of September 30, 2015, the total number of common shares that may be issued under all equity award plans is 3,594,627 and 1,342,719 shares remain available for future grants.

In August 2014, the Company entered into both a separation agreement with an employee and a consulting agreement for continued services to the Company upon the separation date of December 31, 2014. As a result of the change in employment status to a consultant effective January 1, 2015, the Company recorded approximately $0.3 million of stock compensation expense during the first nine months of 2015.

During the first nine months of 2015, the Company granted 913,050 stock options to employees, 35,000 stock options to directors and 27,875 RSUs to employees.

Stock Options

On March 6, 2015, the Company issued 479,750 stock options to employees. Options granted by the Company vest over periods of between 12 and 48 months. 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 (as defined) or grant date, subject to the employee’s continuous service with the Company. Options generally expire ten years after the date of grant.

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 Vesting Commencement Date (as defined), then ratably on the first day of each calendar quarter for 12 quarters, subject to continuous service by the individual and achievement of the performance target. Due to the nature of the performance condition, the Company had concluded that the performance condition was not probable of achievement and therefore, recognition of compensation cost had been deferred until the occurrence of a liquidity event, as defined. The liquidity event occurred upon the closing of the Company’s IPO on March 25, 2014. Accordingly, the Company recognized $0.1 million of compensation expense on March 25, 2014 related to the restricted stock awards with a requisite service period that was complete upon grant. Compensation expense related to the remainder of the restricted stock awards is being recognized over the associated requisite service period commencing on March 25, 2014. The Company recorded approximately $61,000 of stock-based compensation expense related to restricted stock during the third quarter of 2015 and approximately $0.6 million of stock-based compensation during the first nine months of 2015.

Restricted Stock Units

On March 6, 2015, the Company issued 27,875 RSUs to employees. The RSUs vest 100% on the three year anniversary. Total stock-compensation expense to be recognized over the life of the RSUs is $0.3 million and will be recognized on a straight-line basis over the vesting period. The Company recorded approximately $13,000 of stock-based compensation expense related to the RSUs during the third quarter of 2015 and approximately $44,000 of stock-based compensation during the first nine months of 2015.

Compensation Expense Summary

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


	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
	(in thousands)				(in thousands)
Research and development	$	468	$	583	$	1,431	$	2,490
General and administrative		694		652		1,955		2,635
Total	$	1,162	$	1,235	$	3,386	$	5,125

Compensation expense by type of award:


	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
	(in thousands)				(in thousands)
Stock options	$	1,065	$	554	$	2,673	$	1,330
Restricted stock		61		681		604		3,795
Restricted stock units		13		—		44		—
Employee stock purchase plan		23		—		65		—
Total	$	1,162	$	1,235	$	3,386	$	5,125

Included in the compensation expense for the nine months ended September 30, 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 compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References+ Details

Net Loss per Share

9 Months Ended

Sep. 30, 2015

Earnings Per Share [Abstract]

Net Loss per Share

10. Net Loss per Share

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


	Three months ended						Nine months ended
	September 30, 2015			September 30, 2014			September 30, 2015			September 30, 2014
	(in thousands, except share and per share data)						(in thousands, except share and per share data)
Numerator:
Net loss	$	(19,475	)	$	(9,348	)	$	(40,859	)	$	(26,664	)
Accretion on preferred stock		—			—			—			(86,899	)
Net loss applicable to common stockholders	$	(19,475	)	$	(9,348	)	$	(40,859	)	$	(113,563	)

Denominator:
Weighted-average number of common shares – basic and diluted		28,784,231			19,691,167			25,175,077			13,920,651
Net loss per share applicable to common stockholders – basic and diluted	$	(0.68	)	$	(0.47	)	$	(1.62	)	$	(8.16	)

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:

	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
Outstanding stock options		2,251,908		1,596,538		2,251,908		1,596,538
Unvested restricted stock		265,402		563,810		265,402		563,810
Unvested restricted stock units		24,425		—		24,425		—
Total		2,541,735		2,160,348		2,541,735		2,160,348

- Definition

The entire disclosure for earnings per share.

+ References+ Details

Employee Retirement Plan	9 Months Ended
Employee Retirement Plan	Sep. 30, 2015
Compensation And Retirement Disclosure [Abstract]
Employee Retirement Plan	11. Employee Retirement Plan During 2008, the Company established a retirement plan (the Plan) authorized by Section 401(k) of the Internal Revenue Code. In accordance with the Plan, all employees who have attained the age of 21 are eligible to participate in the Plan as of the first Entry Date, as defined, following their date of employment. Each employee can contribute a percentage of compensation up to a maximum of the statutory limits per year. Company contributions are discretionary, contributions in the amount of approximately $71,000 and $0 were made during the three months ended September 30, 2015 and 2014, respectively.

- Definition

The entire disclosure for pension and other postretirement benefits.

+ References+ Details

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2015
Subsequent Events [Abstract]
Subsequent Event	12. Subsequent Event During the period October 1, 2015 through November 5, 2015, the Company sold an additional 372,058 shares pursuant to the Sales Agreement with Cantor Fitzgerald & Co. The aggregate net proceeds received by the Company were approximately $3.9 million, net of commissions.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2015

Accounting Policies [Abstract]

Conversion of Redeemable Preferred Stock

Basis of Presentation

Recent Accounting Pronouncements

Segment Information

Use of Estimates

Cash and Cash Equivalents

Investments

Research and Development

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 September 30, 2015 and December 31, 2014.

	Useful Life	September 30, 2015			December 31, 2014
		(in thousands)
Computer equipment and software	3	$	237		$	99
Furniture and fixtures	5		243			117
Equipment	7		46			6
Leasehold improvements	Shorter of the useful life or remaining lease term (3 years)		64			27
Office equipment under capital lease	3		24			12
			614			261
Less accumulated depreciation			(135	)		(51	)
Net property and equipment		$	479		$	210

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2015

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 September 30, 2015 and December 31, 2014.

	Useful Life	September 30, 2015			December 31, 2014
		(in thousands)
Computer equipment and software	3	$	237		$	99
Furniture and fixtures	5		243			117
Equipment	7		46			6
Leasehold improvements	Shorter of the useful life or remaining lease term (3 years)		64			27
Office equipment under capital lease	3		24			12
			614			261
Less accumulated depreciation			(135	)		(51	)
Net property and equipment		$	479		$	210

Available for Sale Securities (Tables)

9 Months Ended

Sep. 30, 2015

Investments Debt And Equity Securities [Abstract]

Summary of Available for Sale Securities at Fair Value

Available for sale securities at September 30, 2015 and December 31, 2014 consist of the following:

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
September 30, 2015
Cash and cash equivalents:
Cash and money market account	$	66,712	$	—	$	—		$	66,712
Total cash and cash equivalents	$	66,712	$	—	$	—		$	66,712
Available for sale securities:
Certificates of deposit	$	20,170	—		—			$	20,170
U.S. Government debt securities		48,531		15		(6	)		48,540
Corporate debt securities		22,060		5		(21	)		22,044
Total available for sale securities	$	90,761	$	20	$	(27	)	$	90,754
Total cash, cash equivalents, and available for sale securities	$	157,473	$	20	$	(27	)	$	157,466

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2014
Cash and cash equivalents:
Cash and money market account	$	32,780	$	—	$	—		$	32,780
Total cash and cash equivalents	$	32,780	$	—	$	—		$	32,780
Available for sale securities:
Certificates of deposit	$	13,429	—			—		$	13,429
U.S. Government debt securities		38,412		1		(28	)		38,385
Commercial paper		2,499		—		—			2,499
Corporate debt securities		21,854		3		(32	)		21,825
Total available for sale securities	$	76,194	$	4	$	(60	)	$	76,138
Total cash, cash equivalents, and available for sale securities	$	108,974	$	4	$	(60	)	$	108,918

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 September 30, 2015, by contractual maturity, is as follows:

Due in one year or less	$	39,783
Due after one year		50,971
Total available for sale securities	$	90,754

- 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)

9 Months Ended

Sep. 30, 2015

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 September 30, 2015 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Cash and cash equivalents	$	66,712	$	—	$	—	$	66,712
Certificates of deposit		—		20,170		—		20,170
U.S. Government debt securities		—		48,540		—		48,540
Corporate debt securities		—		22,044		—		22,044
	$	66,712	$	90,754	$	—	$	157,466

Assets measured or disclosed at fair value on a recurring basis as of December 31, 2014 are summarized below:

	Fair Value Measurements Using
	Level 1		Level 2		Level 3		Total
	(in thousands)
Assets:
Cash and cash equivalents	$	32,780	$	—	$	—	$	32,780
Certificates of deposit		—		13,429		—		13,429
U.S. Government debt securities		—		38,385		—		38,385
Commercial paper		—		2,499		—		2,499
Corporate debt securities		—		21,825		—		21,825
	$	32,780	$	76,138	$	—	$	108,918

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2015

Payables And Accruals [Abstract]

Components of Accrued Expenses

Accrued expenses are as follows:

	September 30,		December 31,
	2015		2014
	(in thousands)
Professional fees	$	5,785	$	2,460
Accrued bonus		1,240		1,286
Accrued vacation		258		177
Accrued severance		29		179
Accrued payroll		582		213
Other		999		549
Total accrued expenses	$	8,893	$	4,864

Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2015

Equity [Abstract]

Summary of Reserved Shares of Common Stock for Future Issuance

As of September 30, 2015 and December 31, 2014 based on the authorized shares for each series, the Company has reserved the following shares of common stock for future issuance:

	September 30,		December 31,
	2015		2014
Options to purchase common stock		2,251,908		1,526,346
Shares available for future issuance		1,342,719		1,549,154
Total		3,594,627		3,075,500

- Definition

Tabular disclosure of temporary equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

+ References+ Details

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2015

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Payments Required Under Leases

At September 30, 2015, the Company’s future minimum payments required under these leases are as follows:

	Operating		Capital
	Lease		Lease		Total
	(in thousands)
2015	$	230	$	2	$	232
2016		936		8		944
2017		—		5		5
2018		—		1		1
Total	$	1,166		16	$	1,182
Less amount representing interest				—
Present value of minimum lease payments at September 30, 2015			$	16

- 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

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2015

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Compensation Cost Related to Share-Based Awards

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


	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
	(in thousands)				(in thousands)
Research and development	$	468	$	583	$	1,431	$	2,490
General and administrative		694		652		1,955		2,635
Total	$	1,162	$	1,235	$	3,386	$	5,125

Schedule of Compensation Expense by Type of Award

Compensation expense by type of award:


	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
	(in thousands)				(in thousands)
Stock options	$	1,065	$	554	$	2,673	$	1,330
Restricted stock		61		681		604		3,795
Restricted stock units		13		—		44		—
Employee stock purchase plan		23		—		65		—
Total	$	1,162	$	1,235	$	3,386	$	5,125

- Definition

Tabular disclosure of components of a stock option or other award plan under which equity-based compensation is awarded to employees, typically comprised of the amount of unearned compensation (deferred compensation cost), compensation expense, and changes in the quantity and fair value of the shares (or other type of equity) granted, exercised, forfeited, and issued and outstanding pertaining to that plan. Disclosure may also include nature and general terms of such arrangements that existed during the period and potential effects of those arrangements on shareholders, effect of compensation cost arising from equity-based payment arrangements on the income statement, method of estimating the fair value of the goods or services received, or the fair value of the equity instruments granted, during the period, cash flow effects resulting from equity-based payment arrangements and, for registrants that accelerate vesting of out of the money share options, reasons for the decision to accelerate.

+ References+ Details

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2015

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:


	Three months ended						Nine months ended
	September 30, 2015			September 30, 2014			September 30, 2015			September 30, 2014
	(in thousands, except share and per share data)						(in thousands, except share and per share data)
Numerator:
Net loss	$	(19,475	)	$	(9,348	)	$	(40,859	)	$	(26,664	)
Accretion on preferred stock		—			—			—			(86,899	)
Net loss applicable to common stockholders	$	(19,475	)	$	(9,348	)	$	(40,859	)	$	(113,563	)

Denominator:
Weighted-average number of common shares – basic and diluted		28,784,231			19,691,167			25,175,077			13,920,651
Net loss per share applicable to common stockholders – basic and diluted	$	(0.68	)	$	(0.47	)	$	(1.62	)	$	(8.16	)

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:

	Three months ended				Nine months ended
	September 30, 2015		September 30, 2014		September 30, 2015		September 30, 2014
Outstanding stock options		2,251,908		1,596,538		2,251,908		1,596,538
Unvested restricted stock		265,402		563,810		265,402		563,810
Unvested restricted stock units		24,425		—		24,425		—
Total		2,541,735		2,160,348		2,541,735		2,160,348

Nature of Organization and Operations - Additional Information (Details) (USD $)	0 Months Ended	9 Months Ended			3 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended	0 Months Ended		1 Months Ended
	Mar. 06, 2014	Sep. 30, 2015	Dec. 31, 2014	Mar. 25, 2014	Sep. 30, 2015 Cantor Fitzgerald & Co	Aug. 31, 2015 Cantor Fitzgerald & Co Maximum	Mar. 25, 2014 IPO	Apr. 30, 2015 Follow-on public offering	Mar. 25, 2014 Common Stock IPO	Mar. 25, 2014 Common Stock Overallotment option granted to underwriters	Apr. 30, 2015 Common Stock Overallotment option granted to underwriters	Apr. 30, 2015 Common Stock Follow-on public offering
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares					1,311,562				6,762,000	879,647	1,090,909	8,363,636
Sale of stock, price per share							$ 17.00	$ 8.25
Proceeds from issuance of initial public offering							$ 104,400,000	$ 64,600,000
Convertible redeemable preferred stock converted into common stock							12,115,183
Common stock, shares authorized		175,000,000	175,000,000	175,000,000
Preferred stock, shares authorized		25,000,000	25,000,000	25,000,000
Common stock sales agreement amount						50,000,000
Proceeds from sale of common stock, net of commissions					14,200,000
Cash and cash equivalents and available for sale securities		$ 157,466,000	$ 108,918,000
Stock split, conversion ratio	1.75
Entity incorporation date		Feb. 27, 2007

Summary of Significant Accounting Policies - Additional Information (Details) (USD $)	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 25, 2014	Sep. 30, 2015 Segment	Sep. 30, 2014
Summary Of Significant Accounting Policies [Line Items]
Accretion on preferred stock			$ 86,899,000		$ 86,899,000
Number of operating segments				1
Revenue				0
Expected dividend yield				0.00%
Depreciation expense	$ 35,000	$ 13,000		$ 85,000	$ 33,000
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
IPO
Summary Of Significant Accounting Policies [Line Items]
Convertible redeemable preferred stock converted into common stock			12,115,183

Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 614	$ 261
Less accumulated depreciation	(135)	(51)
Net property and equipment	479	210
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	237	99
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	243	117
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	46	6
Leasehold improvements
Property, Plant and Equipment [Line Items]
Leasehold improvements, Useful Life	Shorter of the useful life or remaining lease term (3 years)
Gross property, plant and equipment	64	27
Leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 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	$ 24	$ 12

Available for Sale Securities - Summary of Available for Sale Securities at Fair Value (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 90,761	$ 76,194
Gross Unrealized Gains	20	4
Gross Unrealized Losses	(27)	(60)
Fair Value	90,754	76,138
Cash and cash equivalents	66,712	32,780	49,668	21,215
Cash and cash equivalents, fair value	66,712	32,780
Total cash, cash equivalents, and available for sale securities - Amortized Cost	157,473	108,974
Cash and cash equivalents and available for sale securities	157,466	108,918
U.S. Government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	48,531	38,412
Gross Unrealized Gains	15	1
Gross Unrealized Losses	(6)	(28)
Fair Value	48,540	38,385
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	20,170	13,429
Fair Value	20,170	13,429
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		2,499
Fair Value		2,499
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,060	21,854
Gross Unrealized Gains	5	3
Gross Unrealized Losses	(21)	(32)
Fair Value	22,044	21,825
Cash And Money Market Account
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	66,712	32,780
Cash and cash equivalents, fair value	$ 66,712	$ 32,780

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

+ References+ Details

- Definition

Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

+ References+ Details

Available for Sale Securities - Estimated Fair Value of Available for Sale Securities by Contractual Maturity (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 39,783
Due after one year	50,971
Total available for sale securities	$ 90,754	$ 76,138

Accrued Expenses - Components of Accrued Expenses (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Professional fees	$ 5,785	$ 2,460
Accrued bonus	1,240	1,286
Accrued vacation	258	177
Accrued severance	29	179
Accrued payroll	582	213
Other	999	549
Total accrued expenses	$ 8,893	$ 4,864

- Definition

Carrying value as of the balance sheet date of obligations incurred and payable for incentive compensation awarded to employees and directors or earned by them based on the terms of one or more relevant arrangements. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References+ Details

- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

+ References+ Details

Accrued Expenses - Additional Information (Details) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Accrued Expenses [Line Items]
Severance agreement description		In August 2014, the Company entered into a separation agreement with an employee, which became effective on August 13, 2014. The Company will record the expense and liability associated with the separation agreement ratably over the period from August 5, 2014 through December 31, 2015 because the severance payments are subject to continued service and forfeiture until December 31, 2015. During the third quarter of 2014, the Company recorded severance expense in the amount of $46,682, which was recorded to research and development expense and will be paid out beginning January 2015 through December 2015.
Severance expense	$ 73,000
Paid Out Through December 2015
Accrued Expenses [Line Items]
Payment out of severance accrual		$ 287,000
Payment date for severance costs		will be paid out through December 2015

- Definition

Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

+ References+ Details

Stockholders' Equity - Additional Information (Details) (USD $)	0 Months Ended
	Mar. 06, 2014	Sep. 30, 2015	Dec. 31, 2014	Mar. 25, 2014
Equity [Abstract]
Common stock, shares authorized		175,000,000	175,000,000	175,000,000
Common stock, par value		$ 0.00001	$ 0.00001
Preferred stock, shares authorized		25,000,000	25,000,000	25,000,000
Preferred stock, par value		$ 0.00001	$ 0.00001
Stock split, conversion ratio	1.75

Income Taxes - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended
Income Taxes - Additional Information (Details) (USD $)	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Income tax provisions or benefits	$ 0	$ 0	$ 0	$ 0

Commitments and Contingencies - Additional Information (Details) (USD $)	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2014 sqft	Dec. 31, 2013 sqft	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014 sqft
Commitments And Contingencies Disclosure [Abstract]
Lease period		3 years
Area of property leased	8,530	6,837					8,530
Monthly lease payments	$ 45,000	$ 31,000			$ 32,000
Rent abatement		31,000
Lease commenced and rental payments period		2014-01
Cash-collateralized irrevocable standby letter of credit		125,345	125,345		125,345
Lease space occupancy date	Mar. 13, 2015
Lease expiration date					Dec. 31, 2016
Landlord contribution for leasehold improvements	100,000						100,000
Additional cash security deposit paid to landlord	179,130						179,130
Capital lease term					3 years
Capital lease commencement period					2014-02
Rent expense associated with lease			200,000	100,000	600,000	300,000
Contract cost incurred in research and development activities					$ 19,600,000		$ 4,300,000

Commitments and Contingencies - Schedule of Future Minimum Payments Required Under Leases (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2015	$ 230
Operating Lease, 2016	936
Operating Lease, 2017	0
Operating Lease, 2018	0
Operating Lease, Total	1,166
Capital Lease, 2015	2
Capital Lease, 2016	8
Capital Lease, 2017	5
Capital Lease, 2018	1
Capital Lease	16
Capital Lease, Present value of minimum lease payments at September 30, 2015	16
Operating and Capital Lease, 2015	232
Operating and Capital Lease, 2016	944
Operating and Capital Lease, 2017	5
Operating and Capital Lease, 2018	1
Operating and Capital Lease, Total	$ 1,182

Stock-Based Compensation - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended						3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	0 Months Ended	3 Months Ended		9 Months Ended			0 Months Ended		3 Months Ended		9 Months Ended		0 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Sep. 30, 2014 Employee Severance	Sep. 30, 2015 Consultant	Sep. 30, 2015 Employees	Sep. 30, 2015 Director	Sep. 30, 2015 Shares available for future issuance	Dec. 31, 2014 Shares available for future issuance	Sep. 30, 2015 Restricted Stock Units	Sep. 30, 2015 Restricted Stock Units	Sep. 30, 2015 Restricted Stock Units Tranche One	Sep. 30, 2015 Restricted Stock Units Employees	Mar. 06, 2015 Stock Options	Sep. 30, 2015 Stock Options	Sep. 30, 2014 Stock Options	Sep. 30, 2015 Stock Options	Sep. 30, 2014 Stock Options	Sep. 30, 2015 Stock Options Tranche One	Mar. 25, 2014 Restricted Stock	Dec. 23, 2013 Restricted Stock	Sep. 30, 2015 Restricted Stock	Sep. 30, 2014 Restricted Stock	Sep. 30, 2015 Restricted Stock	Sep. 30, 2014 Restricted Stock	Dec. 23, 2013 Restricted Stock Tranche One	Dec. 23, 2013 Restricted Stock Employees	Dec. 23, 2013 Restricted Stock Non-Employees	Sep. 30, 2015 Maximum Stock Options	Sep. 30, 2015 Maximum Stock Options Director	Sep. 30, 2015 Maximum Non Employee Stock Options	Sep. 30, 2015 Minimum Stock Options	Sep. 30, 2015 Minimum Stock Options Director	Sep. 30, 2015 Minimum Non Employee Stock Options	Sep. 30, 2015 2014 Plans	Sep. 30, 2015 2014 Plans Maximum	Sep. 30, 2015 2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares reserved for future issuance	3,594,627		3,594,627		3,075,500					1,342,719	1,549,154																										1,785,000	1,131,937
Incremental rate at which the shares reserved for issuance increase																																					3.00%
Maximum shares of common stock authorized to be issued	3,594,627		3,594,627																																				262,500
Stock-based compensation expense	$ 1,162,000	$ 1,235,000	$ 3,386,000	$ 5,125,000		$ 1,000,000	$ 300,000					$ 13,000	$ 44,000				$ 1,065,000	$ 554,000	$ 2,673,000	$ 1,330,000		$ 100,000		$ 61,000	$ 681,000	$ 604,000	$ 3,795,000
Granted shares								913,050	35,000
Granted shares of restricted stock															27,875														450,224	79,067
Shares issued																479,750
Vesting periods												3 years							1 year				1 year								48 months	48 months	48 months	12 months	12 months	12 months
Vesting percentage														100.00%							25.00%							25.00%
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 (as defined) or grant date, subject to the employee’s continuous service with the Company
Options expiration after the date of grant																			10 years
Granted, Weighted-Average Grant Date Fair Value																							$ 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 Vesting Commencement Date (as defined), 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
Total compensation cost to be recognized												$ 300,000	$ 300,000

Stock-Based Compensation - Compensation Cost Related to Share-Based Awards (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,162,000	$ 1,235,000	$ 3,386,000	$ 5,125,000
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	468,000	583,000	1,431,000	2,490,000
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 694,000	$ 652,000	$ 1,955,000	$ 2,635,000

Stock-Based Compensation - Schedule of Compensation Expense by Type of Award (Details) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended
	Mar. 25, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		$ 1,162,000	$ 1,235,000	$ 3,386,000	$ 5,125,000
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		1,065,000	554,000	2,673,000	1,330,000
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	100,000	61,000	681,000	604,000	3,795,000
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		13,000		44,000
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense		$ 23,000		$ 65,000

Net Loss per Share - Calculation of Basic and Diluted Net Loss per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 25, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net loss	$ (19,475)	$ (9,348)		$ (40,859)	$ (26,664)
Accretion on preferred stock			(86,899)		(86,899)
Net loss applicable to common stockholders	$ (19,475)	$ (9,348)		$ (40,859)	$ (113,563)
Denominator:
Weighted-average number of common shares – basic and diluted	28,784,231	19,691,167		25,175,077	13,920,651
Net loss per share applicable to common stockholders—basic and diluted	$ (0.68)	$ (0.47)		$ (1.62)	$ (8.16)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References+ Details

Net Loss per Share - Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	2,541,735	2,160,348	2,541,735	2,160,348
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	2,251,908	1,596,538	2,251,908	1,596,538
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	265,402	563,810	265,402	563,810
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	24,425		24,425

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References+ Details

Employee Retirement Plan - Additional Information (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015
Compensation And Retirement Disclosure [Abstract]
Employers contributions to defined contribution plan	$ 71,000	$ 0
Employees eligibility age to participate in retirement plan			21 years

Subsequent Event - Additional Information (Details) (Cantor Fitzgerald & Co, USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	1 Months Ended
	Sep. 30, 2015	Nov. 05, 2015 Subsequent Event
Subsequent Event [Line Items]
Issuance of common stock, shares	1,311,562	372,058
Proceeds from issuance of initial public offering		$ 3.9

Fair Value of Financial Instruments - Assets Measured or Disclosed at Fair Value on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 157,466	$ 108,918
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	48,540	38,385
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	66,712	32,780
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	90,754	76,138
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	48,540	38,385
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	66,712	32,780
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	66,712	32,780
Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	20,170	13,429
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	20,170	13,429
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis		2,499
Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis		2,499
Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	22,044	21,825
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	$ 22,044	$ 21,825

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details)	Sep. 30, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	3,594,627	3,075,500
Options to purchase common stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	2,251,908	1,526,346
Shares available for future issuance
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	1,342,719	1,549,154