Akebia Therapeutics (AKBA) 10-Q 8 Aug 16 2016 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Jul. 31, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q2
Trading Symbol	AKBA
Entity Registrant Name	Akebia Therapeutics, Inc.
Entity Central Index Key	1,517,022
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		38,011,604

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 46,177	$ 49,778
Available for sale securities	142,472	88,676
Prepaid expenses and other current assets	3,873	2,563
Total current assets	192,522	141,017
Property and equipment, net	1,832	540
Deferred offering costs		102
Other assets	1,281	1,281
Total assets	195,635	142,940
Current liabilities:
Accounts payable	5,143	2,313
Accrued expenses	15,789	9,555
Total current liabilities	20,932	11,868
Deferred rent	1,406	69
Deferred revenue	40,000
Other non-current liabilities	9	5
Total liabilities	62,347	11,942
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized at June 30, 2016 and December 31, 2015; 0 shares issued and outstanding at June 30, 2016 and December 31, 2015
Common stock: $0.00001 par value; 175,000,000 shares authorized at June 30, 2016 and December 31, 2015; 38,008,933 and 30,662,218 shares issued and outstanding at June 30, 2016 and December 31, 2015, respectively	0	0
Additional paid-in capital	356,217	292,783
Treasury stock, at cost, 0 shares in 2016, 8,643 shares in 2015		(162)
Accumulated other comprehensive income (loss)	37	(234)
Accumulated deficit	(222,966)	(161,389)
Total stockholders' equity	133,288	130,998
Total liabilities and stockholders' equity	$ 195,635	$ 142,940

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	25,000,000	25,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	175,000,000	175,000,000
Common stock, shares issued	38,008,933	30,662,218
Common stock, shares outstanding	38,008,933	30,662,218
Treasury Stock, shares	0	8,643

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Operating expenses:
Research and development	$ 30,877	$ 6,505	$ 51,112	$ 13,168
General and administrative	5,311	4,384	11,122	8,617
Total operating expenses	36,188	10,889	62,234	21,785
Operating loss	(36,188)	(10,889)	(62,234)	(21,785)
Other income (expense):
Interest income	270	116	504	212
Other income	139	84	153	189
Net loss	$ (35,779)	$ (10,689)	$ (61,577)	$ (21,384)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.95)	$ (0.40)	$ (1.65)	$ (0.92)
Weighted-average number of common shares used in net loss per share applicable to common stockholders—basic and diluted	37,811,056	26,614,671	37,342,324	23,340,590
Comprehensive loss:
Net loss	$ (35,779)	$ (10,689)	$ (61,577)	$ (21,384)
Other comprehensive income (loss) - unrealized gain (loss) on securities	63	(19)	37	(27)
Comprehensive loss	$ (35,716)	$ (10,708)	$ (61,540)	$ (21,411)

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities:
Net loss	$ (61,577)	$ (21,384)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	78	50
Amortization of premium/discount on investments	287	271
Stock-based compensation	2,473	2,223
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,311)	(610)
Accounts payable	2,830	391
Accrued expense	6,362	(1,378)
Deferred revenue	40,000
Deferred rent	1,337	(27)
Net cash used in operating activities	(9,521)	(20,464)
Investing activities:
Purchase of equipment	(1,358)	(227)
Proceeds from the maturities of available for sale securities	64,874	34,790
Purchase of available for sale securities	(118,684)	(35,434)
Net cash used in investing activities	(55,168)	(871)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	60,869	64,624
Proceeds from the sale of stock under employee stock purchase plan	105	109
Proceeds from the exercise of stock options	120	73
Payments on capital lease obligations	(6)	(3)
Net cash provided by financing activities	61,088	64,803
Decrease in cash and cash equivalents	(3,601)	43,468
Cash and cash equivalents at beginning of the period	49,778	32,780
Cash and cash equivalents at end of the period	46,177	76,248
Non-cash financing activities
Unpaid follow-on offering costs	$ 131
Assets acquired under capital lease		$ 12

Nature of Organization and Oper

Nature of Organization and Operations	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations Incorporated in Delaware in 2007, Akebia Therapeutics, Inc. (Akebia, or the Company) is a biopharmaceutical company focused on the development of novel proprietary therapeutics based on hypoxia inducible factor, or HIF, biology and the commercialization of these products for patients with serious unmet medical needs. HIF is the primary regulator of the production of red blood cells, or RBCs, in the body and a potentially novel mechanism for the treatment of anemia secondary to chronic kidney disease, or CKD. Pharmacologic modulation of the HIF pathway may also have broader therapeutic applications in acute renal failure, organ protection, ischemia-reperfusion injury, cancer, ophthalmology, and inflammatory diseases. The Company’s lead product candidate, vadadustat, formerly known as AKB-6548, is The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates and undertaking preclinical and clinical studies. The Company has not generated any product revenue to date and may never generate any product revenue in the future. The Company’s product candidates are subject to long development cycles and the Company may be unsuccessful in its efforts to develop, obtain regulatory approval for or market its product candidates. The Company is subject to a number of risks including, but not limited to, the need to obtain adequate additional funding, including the resources necessary to fund its recently commenced global Phase 3 development of vadadustat in non-dialysis and dialysis patients with anemia related to CKD. In December 2015, the Company began dosing patients in its Phase 3 vadadustat program in non-dialysis patients, PRO 2 2 2 2 2 2 The Company is also subject to a number of other risks including possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, the development of new technological innovations by competitors, the need to successfully commercialize and gain market acceptance of any of the Company’s products that are approved and uncertainty around intellectual property matters. If the Company does not successfully commercialize any of its products, it will be unable to generate product revenue or achieve profitability. In December 2015, the Company entered into a collaboration agreement with Mitsubishi Tanabe to develop and commercialize vadadustat in Japan and certain other countries in Asia for total milestone payments of up to $350.0 million, including up to $100.0 million in upfront and development payments, of which $40.0 million was received in January 2016. If Japanese patients are not included in either the global Phase 3 PRO 2 2 Through the end of 2015 the Company had raised approximately $187.4 million of net proceeds from three underwritten public offerings, including our initial public offering. In January 2016, the Company completed a follow-on public offering whereby the Company sold 7,250,000 shares of common stock at a price of $9.00 per share. The aggregate net proceeds received by the Company from the offering were approximately $61.0 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. In May 2016, the Company entered into a Sales Agreement with Cantor Fitzgerald & Co. to periodically sell up to $75 million of shares of common stock in an at-the-market, or ATM, offering. During the second quarter of 2016, there were no sales of common stock pursuant to the Sales Agreement. The Company believes that its cash, cash equivalents and available for sale securities of $188.6 million as of June 30, 2016 is sufficient to fund its current operating plan through the second quarter of 2017. 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. As of June 30, 2016, the Company had cash and cash equivalents of approximately $188.6 million and current accounts payable and accrued expenses of $20.9 million. The Company has incurred substantial losses since inception, primarily due to investments in research and development, and we expect to continue to incur substantial losses over the next four to five years. Without any additional financings or other transactions, the Company anticipates that it will have sufficient cash available to support its development programs and business operations through the second quarter of 2017. The accompanying financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. In the future, the Company’s ability to continue as a going concern is dependent on its ability to raise additional capital to fund its research and development programs and meet its obligations on a timely basis. As of June 30, 2016, the financial statements do not include any adjustments relating to recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might be necessary should the Company be unable to continue its existence. To potentially mitigate the risk that the Company may be unable to continue as a going concern, it plans to pursue all or a combination of potential strategic alliances, collaboration agreements and other strategic transactions. The Company also may seek additional capital through public or private equity offerings (including its ATM offering), which could have a dilutive impact on stockholders and the issuance, or even potential issuance, of shares could have a negative effect on the market price of common stock. Even if the Company is able to secure additional capital, such financings may only be available on unattractive terms, or could result in significant dilution of stockholders’ interests. If none of the foregoing alternatives is available, or if available, the Company is unable to raise sufficient capital through such transactions, it may be forced to limit or cease its development activities.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies 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 U.S. GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Update (ASU) of the Financial Accounting Standards Board (FASB). In the quarter ended December 31, 2015, the Company identified and corrected an error in the historical classification of certain operating costs between research and development and general and administrative expenses. The Company concluded the effect of this classification error was not material to its consolidated financial statements for any prior period. The classification correction had no effect on the Company’s current or historical total operating expenses or net loss. 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, 2015, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K (File No. 001-36352), which was filed with the Securities and Exchange Commission (SEC) on March 14, 2016. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard-setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting In February 2016, the FASB issued ASU 2016-02, Leases In August 2014, the FASB issued ASU 2014-15, which requires management of public and private companies to evaluate whether there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. If conditions or events raise substantial doubt about an entity’s ability to continue as a going concern, and substantial doubt is not alleviated after consideration of management’s plans, an entity should include a statement in the footnotes indicating that there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. The new standard is effective for annual periods ending after December 15, 2016, and for annual periods and interim periods thereafter. Early application is permitted. While the Company intends to adopt the standard as of December 31, 2016, if this standard had been adopted as of June 30, 2016, management of the Company believes that it would have concluded there is substantial doubt about the Company’s ability to continue as a going concern one year from the date of filing of this Form 10-Q. See Note 1 for additional information on our liquidity risks and management’s plans. In May 2014, the FASB issued a new revenue recognition standard which amends revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The new standard provides a five step framework whereby revenue is recognized when promised goods or services are transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires enhanced disclosures pertaining to revenue recognition in both interim and annual periods. In August 2015, the FASB deferred the effective date of the new revenue standard from January 1, 2017 to January 1, 2018. Early adoption is permitted any time after the original effective date, which for us is January 1, 2017. The standard allows for adoption using a full retrospective method or a modified retrospective method. The Company is currently evaluating the timing, method of adoption and the expected impact that the standard could have on our consolidated financial statements and related disclosures. Segment Information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing and commercializing proprietary therapeutics based on HIF biology. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: prepaid and accrued research and development expense, stock-based compensation expense, accrued expenses and income taxes. Prior to the initial public offering, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company granted stock options at exercise prices not less than the fair market value of its common stock as determined by the Board of Directors contemporaneously at the date such grants were made, with input from management. Prior to the Company’s initial public offering in March 2014, the fair value of common stock at the grant date was adjusted in connection with the Company’s retrospective fair value assessment for financial reporting purposes. Accordingly, the Board of Directors determined the estimated fair value of the Company’s common stock based on a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector and the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale of the Company. 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 June 30, 2016, the Company’s cash is primarily in money market funds. The Company may maintain balances with its banks in excess of federally insured limits. Investments Management determines the appropriate classification of securities at the time of purchase and reevaluates such designation as of each balance sheet date. Currently, the Company classifies all securities as available-for-sale which are included in current assets as they are intended to fund current operations. The Company carries available-for-sale securities at fair value. The Company conducts periodic reviews to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment and its application to certain investments. When assessing whether a decline in the fair value of a security is other-than-temporary, the Company considers the fair market value of the security, the duration of the security’s decline, and prospects for the underlying business. Based on these considerations, the Company did not identify any other-than-temporary unrealized losses at June 30, 2016. Unrealized losses on available-for-sale securities that are determined to be temporary, and not related to credit loss, are recorded in accumulated other comprehensive loss, a component of stockholders’ equity. The amortized cost of debt securities in this category reflects amortization of premiums and accretion of discounts to maturity computed under the effective interest method. The Company includes this amortization in the caption “Interest income” within the consolidated statements of operations and comprehensive loss. The Company also includes in net investment income, realized gains and losses and declines in value determined to be other than temporary. The Company bases the cost of securities sold upon the specific identification method, and includes interest and dividends on securities in interest income. Revenue Recognition To date, the Company has not generated any revenue from the sales of products or other means. For the foreseeable future, the Company expects substantially all of its revenues will be generated from its collaboration with Mitsubishi Tanabe (see Note 9) and any other collaborations the Company may enter into. The Company will recognize revenue in accordance with ASC Topic 605, Revenue Recognition · Persuasive evidence of an arrangement exists; · Delivery has occurred or services have been rendered; · The seller’s price to the buyer is fixed or determinable; and · Collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company evaluates multiple‑element arrangements based on the guidance in ASC Topic 605‑25, Revenue Recognition Multiple‑Element Arrangements The consideration received under the arrangement that is fixed or determinable is then allocated among the separate units of accounting using the relative selling price method. The Company determines the estimated selling price for units of accounting within each arrangement using vendor‑specific objective evidence (VSOE) of selling price, if available, third‑party evidence (TPE) of selling price if VSOE is not available, or best estimate of selling price (BESP) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity‑specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company will recognize arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. In the event that a deliverable does not represent a separate unit of accounting, the Company will recognize revenue from the combined unit of accounting over the Company’s contractual or estimated performance period for the undelivered elements, which is typically the term of the Company’s research and development obligations. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company will recognize revenue under the arrangement on a straight‑line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue to be recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight‑line method or proportional performance method, as applicable, as of the period ending date. At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (1) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (2) the consideration relates solely to past performance and (3) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone and the level of effort and investment required to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are not considered substantive are recognized as earned if there are no remaining performance obligations or over the remaining period of performance, assuming all other revenue recognition criteria are met. Options are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the cost to exercise the option, the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option and the likelihood the option will be exercised. When an option is considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in allocable consideration, assuming the option is not priced at a significant and incremental discount. Conversely, when an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount would be included as a deliverable at the inception of the arrangement. The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met. 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 ASC Topic 740, Income Taxes 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 June 30, 2016 and 2015, the Company does not have any significant uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. Stock-Based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation Equity-Based Payments to Non-Employees The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of company-specific historical and implied volatility data for trading the Company’s stock in the public market, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company is in the product development stage with no 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. ASC Topic 820, Fair Value Measurements and Disclosures Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments, and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below: · Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. · Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active, or for which all significant inputs are observable, either directly or indirectly. · Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Items measured at fair value on a recurring basis include short-term investments (see Note 4). The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The rate implicit within the Company’s capital lease obligation approximates market interest rates. Concentrations of Credit Risk and Off-Balance Sheet Risk Cash and investments are the only financial instruments that potentially subject the Company to concentrations of credit risk. The Company maintains its cash with high quality, accredited financial institutions and, accordingly, such funds are subject to minimal credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements. Net Loss per Share Basic net loss per share is calculated by dividing net loss attributable to common stockholders by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the diluted net loss per share calculation, preferred stock, stock options, unvested restricted stock and RSUs are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Property and Equipment Property and equipment is stated at cost, less accumulated depreciation. Assets under capital lease are included in property and equipment. Property and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors, operating losses, unused capacity, market value declines and technological obsolescence. Recorded values of asset groups of equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale). The following is the summary of property and equipment and related accumulated depreciation as of June 30, 2016 and December 31, 2015. Useful Life June 30, 2016 December 31, 2015 (in thousands) Computer equipment and software 3 $ 618 $ 300 Furniture and fixtures 5 475 243 Equipment 7 50 50 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 878 70 Office equipment under capital lease 3 36 24 2,057 687 Less accumulated depreciation (225 ) (147 ) Net property and equipment $ 1,832 $ 540 Depreciation expense, including expense associated with assets under capital leases, was approximately $46,000 and $32,000 for the three months ended June 30, 2016 and 2015, respectively and $78,000 and $50,000 for the six months ended June 30, 2016 and 2015, respectively.

Available for Sale Securities

Available for Sale Securities	6 Months Ended
	Jun. 30, 2016
Investments Debt And Equity Securities [Abstract]
Available for Sale Securities	3. Available for sale securities Available for sale securities at June 30, 2016 and December 31, 2015 consist of the following : Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) June 30, 2016 Cash and cash equivalents $ 46,177 $ — $ — $ 46,177 Available for sale securities: Certificates of deposit $ 19,063 — — $ 19,063 U.S. Government debt securities 111,004 38 (5 ) 111,037 Corporate debt securities 12,368 5 (1 ) 12,372 Total available for sale securities $ 142,435 $ 43 $ (6 ) $ 142,472 Total cash, cash equivalents, and available for sale securities $ 188,612 $ 43 $ (6 ) $ 188,649 Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) December 31, 2015 Cash and cash equivalents $ 49,778 $ — $ — $ 49,778 Available for sale securities: Certificates of deposit $ 21,505 — — $ 21,505 U.S. Government debt securities 46,461 — (185 ) 46,276 Corporate debt securities 20,944 1 (50 ) 20,895 Total available for sale securities $ 88,910 $ 1 $ (235 ) $ 88,676 Total cash, cash equivalents, and available for sale securities $ 138,688 $ 1 $ (235 ) $ 138,454 The estimated fair value of the Company’s available for sale securities balance at June 30, 2016, by contractual maturity, is as follows: Due in one year or less $ 114,894 Due after one year 27,578 Total available for sale securities $ 142,472

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	4. Fair Value of Financial Instruments The Company utilizes a portfolio management company for the valuation of the majority of its investments. This company is an independent, third-party vendor recognized to be an industry leader with access to market information that obtains or computes fair market values from quoted market prices, pricing for similar securities, recently executed transactions, cash flow models with yield curves and other pricing models. For valuations obtained from the pricing service, the Company performs due diligence to understand how the valuation was calculated or derived, focusing on the valuation technique used and the nature of the inputs. Based on the fair value hierarchy, the Company classifies its cash equivalents and 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 June 30, 2016 and December 31, 2015 are summarized below: Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) June 30, 2016 Assets: Cash and cash equivalents $ 46,177 $ — $ — $ 46,177 Certificates of deposit — 19,063 — 19,063 U.S. Government debt securities — 111,037 — 111,037 Corporate debt securities — 12,372 — 12,372 $ 46,177 $ 142,472 $ — $ 188,649 Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) December 31, 2015 Assets: Cash and cash equivalents $ 49,778 $ — $ — $ 49,778 Certificates of deposit — 21,505 — 21,505 U.S. Government debt securities — 46,276 — 46,276 Corporate debt securities — 20,895 — 20,895 $ 49,778 $ 88,676 $ — $ 138,454 The Company had no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) at June 30, 2016 and December 31, 2015. The Company’s corporate debt securities are all investment grade. 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.

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2016
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses are as follows: June 30, 2016 December 31, 2015 (in thousands) Accrued clinical $ 10,692 $ 4,536 Accrued bonus 1,250 2,178 Professional fees 761 647 Accrued vacation 433 310 Accrued payroll 410 518 Accrued severance 196 — Other 2,047 1,366 Total accrued expenses $ 15,789 $ 9,555 In January 2016, the Company entered into separation agreements with two employees. During the first quarter of 2016, the Company recorded severance expense in the amount of $0.4 million, of which $0.2 million was recorded to general and administrative expense and $0.2 million was recorded to research and development expense. During the three months ended June 30, 2016, approximately $0.1 million was paid out of the severance accrual and during the six months ended June 30, 2016, approximately $0.2 was paid out of the severance accrual.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2016
Equity [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Authorized and Outstanding Capital Stock As of December 31, 2014, the authorized capital stock of the Company included 175,000,000 shares of common stock, par value $0.00001 per share, of which 38,008,933 and 30,662,218 shares are issued and outstanding at June 30, 2016 and December 31, 2015, respectively; and 25,000,000 shares of undesignated preferred stock, par value $0.00001 per share, of which 0 shares are issued and outstanding at June 30, 2016 and December 31, 2015. Equity Plans 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 initial public offering on March 25, 2014. The 2014 Plan replaces the 2008 Equity Incentive Plan (2008 Plan), however, any options or awards outstanding under the 2008 Plan at the time of adoption of the 2014 Plan remain outstanding and effective. The 2014 Plan allows for the granting of stock options, stock appreciation rights, or SARs, restricted stock, unrestricted stock, stock units, performance awards and other awards convertible into or otherwise based on shares of our common stock. Dividend equivalents may also be provided in connection with an award under the 2014 Plan. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2014 Plan. The Company initially reserved 1,785,000 shares of its common stock for the issuance of awards under the 2014 Plan. The 2014 Plan provides that the number of shares reserved and available for issuance under the 2014 Plan will automatically increase annually on January 1 st st st 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 maximum aggregate number of shares of common stock available for purchase pursuant to the exercise of options granted under the ESPP will be the lesser of (a) 262,500 shares, increased on each anniversary of the adoption of the ESPP by one percent (1%) of the total shares of common stock then outstanding and (b) 739,611 shares (which is equal to five percent (5%) of the total shares of common stock outstanding on the date of the adoption of the ESPP on a fully diluted, as converted basis (ESPP Evergreen Provision). Under the ESPP, each offering period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering. The per-share purchase price at the end of each offering period is equal to the lesser of 85% of the closing price of our common stock at the beginning or end of the offering period. Shares Reserved for Future Issuance The Company has reserved for future issuance the following number of shares of common stock: June 30, 2016 December 31, 2015 Unvested restricted common stock 159,640 216,716 Common stock options and RSU's outstanding 3,150,718 2,231,057 Shares available for issuance under the 2014 Plan (1) 1,305,784 1,318,732 Shares available for issuance under the ESPP (2) 803,105 440,304 Total 5,419,247 4,206,809 (1) On January 1, 2016, the shares reserved for future grants under the 2014 Plan increased by 986,800 shares pursuant to the 2014 Plan Evergreen Provision. (2) On February 28, 2016, the shares reserved for future issuance under the ESPP increased by 379,430 shares pursuant to the ESPP Evergreen Provision. Stock-Based Compensation Stock Options On February 22, 2016, as part of the Company’s annual grant of equity, the Company issued 624,275 stock options to employees. In addition, the Company issues stock options to new hires and occasionally to other employees not in connection with the annual grant process. Options granted by the Company vest over periods of between 12 and 48 months. 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. The Company recorded approximately $1.0 million of stock-based compensation expense related to stock options during the three months ended June 30, 2016 and approximately $2.1 million during the six months ended June 30, 2016. 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. Compensation expense related to the restricted stock awards is being recognized over the associated requisite service period which commenced on March 25, 2014. The Company recorded approximately $27,000 of stock-based compensation expense related to restricted stock during the three months ended June 30, 2016 and recorded approximately $13,000 during the six months ended June 30, 2016 as a result of mark to market adjustments related to non-employees. Restricted Stock Units On February 22, 2016, as part of the Company’s annual grant of equity, the Company issued 382,338 RSUs to employees. In addition, the Company occasionally issues RSUs not in connection with the annual grant process to employees. The RSUs vest 100% on the third year anniversary of the grant date. Total stock-compensation expense to be recognized over the life of the RSUs is $2.9 million and will be recognized on a straight-line basis over the vesting period. The Company recorded approximately $0.2 million of stock-based compensation expense related to the RSUs during the three months ended June 30, 2016 and approximately $0.3 million during the six months ended June 30, 2016. ESPP T 16,629 Compensation Expense Summary The Company has recognized the following compensation cost related to share-based awards: Three Months Ended Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 (in thousands) (in thousands) Research and development $ 365 $ 397 $ 757 $ 962 General and administrative 857 698 1,716 1,261 Total $ 1,222 $ 1,095 $ 2,473 $ 2,223 Compensation expense by type of award: Three Months Ended Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 (in thousands) (in thousands) Stock options $ 1,021 $ 908 $ 2,149 $ 1,607 Restricted stock 27 142 13 542 Restricted stock units 158 24 264 32 Employee stock purchase plan 16 21 47 42 Total $ 1,222 $ 1,095 $ 2,473 $ 2,223

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2016
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 or six months ended June 30, 2016 and 2015. 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.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2016
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 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 records a deferred lease obligation 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 First Amendment, for additional office space contiguous to its current office space in Cambridge, Massachusetts. The First Amendment included leasing an additional 8,530 square feet of office space, or the Expansion Space, with an occupancy date of March 13, 2015. The First Amendment provided for additional monthly lease payments of approximately $45,000 for 8,530 square feet for the first twelve months and provided for annual rent escalations thereafter. The monthly rent on the existing 6,837 square feet remained at approximately $32,000 through December 31, 2016, the expiration of the lease. The First Amendment included a contribution from the landlord for leasehold improvements in the amount of approximately $100,000 which was 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 represented the cumulative difference between actual facility lease payments and lease expense recognized ratably over the lease period. In connection with the Amendment, the Company paid an additional cash security deposit to the landlord of $179,130. In November 2015, the Company entered into a Second Amendment to Lease, or the Second Amendment, amending the Lease to extend its existing lease for 16,222 square feet on the 11 th th th th th th th th In July, 2016, the Company entered into a Third Amendment to Lease (see Note 12). The Company recognizes rent expense for the space which it currently occupies under its initial lease, the First Amendment, and the Second Amendment, and records a deferred lease obligation representing the cumulative difference between actual facility lease payments and lease expense recognized ratably over the lease period, which is included in the Company’s condensed consolidated balance sheets as of June 30, 2016 and December 31, 2015. The Company will begin recognizing rent expense for the additional space not yet available at June 30, 2016 subsequent to taking possession of the space . The Company leases office equipment under three year capital leases with payments commencing in February 2014, April 2015 and February 2016, respectively. The capital lease amounts are included in accrued expenses and other liabilities. At June 30, 2016, the Company’s future minimum payments required under these leases are as follows: Operating Capital Lease Lease Total (in thousands) 2016 $ 1,425 $ 6 $ 1,431 2017 3,117 9 3,126 2018 3,117 5 3,122 2019 3,117 — 3,117 2020 3,117 — 3,117 Thereafter 17,664 — 17,664 Total $ 31,557 20 $ 31,577 Less amount representing interest (1 ) Present value of minimum lease payments at June 30, 2016 $ 19 The Company recorded approximately $0.7 million and $0.2 million in rent expense for the three months ended June 30, 2016 and 2015, respectively and $1.0 and $0.4 million in rent expense for the six months ended June 30, 2016 and 2015, respectively. Under the Company’s agreement with Quintiles, Inc., or Quintiles, to provide services for the PRO 2 2 In September 2015, a purported securities class action lawsuit was filed against the Company, including its Chief Executive Officer, its Chief Financial Officer, and members of the Company’s Board of Directors, in the Business Litigation Section of the Suffolk County Superior Court of Massachusetts. The complaint is brought on behalf of an alleged class of those who purchased common stock of the Company pursuant or traceable to the Company’s initial public offering, and purports to allege claims arising under Sections 11, 12(a)(2) and 15 of the Securities Act of 1933, as amended. The complaint generally alleges that the defendants violated the federal securities laws by, among other things, making material misstatements or omissions concerning the Phase 2b clinical study of vadadustat. The complaint seeks, among other relief, unspecified compensatory damages, rescission of certain stock purchases, attorneys’ fees, and costs. In October 2015, the Company removed the case to the United States District Court for the District of Massachusetts, and the plaintiff filed a motion to remand the case back to the Business Litigation Section of the Suffolk County Superior Court of Massachusetts. The plaintiff’s motion to remand was granted in April 2016. The Company believes such claims are without merit and will engage in a vigorous defense of such litigation. The Company has had a number of positive developments in our opposition and invalidity proceedings against FibroGen, Inc., or FibroGen. With regard to the opposition that the Company filed in Europe against FibroGen’s European Patent No. 1463823, or the ’823 patent, an oral proceeding took place March 8 and 9, 2016. Following the oral proceeding, the European Opposition Division ruled that the patent as granted did not meet the requirements for patentability under the European Patent Convention and, therefore, revoked the patent in its entirety. FibroGen has appealed that decision. Likewise, with regard to the invalidity proceeding that the Company filed in Japan against certain claims of FibroGen’s Japanese Patent No. 4804131, or the ’131 patent, which is the Japanese counterpart to the ’823 patent, the Japan Patent Office, or JPO, issued a preliminary decision finding all of the challenged claims to be invalid. FibroGen subsequently amended the claims and the JPO accepted the amendments. The resulting FibroGen Japanese ’131 patent does not cover vadadustat or any pyridine carboxamide compounds. To date, FibroGen has been unsuccessful in its attempts to obtain a patent in the United States covering the same claim scope as it obtained initially in Europe and Japan in the ’823 and ’131 patents. In the event FibroGen were to obtain such a patent in the United States, the Company may decide to challenge them like the Company has done in Europe and Japan. On May 13, 2015, May 20, 2015 and July 6, 2015 the Company filed oppositions to FibroGen’s European Patent Nos. 2322153, 2322155, and 1633333, or the ’153 patent, the ’155 patent, and the ’333 patent, respectively, requesting the patents be revoked in their entirety. These related patents claim, among other things, various compounds that either stabilize HIFα or inhibit a HIF hydroxylase or a HIF prolyl hydroxylase for treating or preventing various conditions, including, inter alia The Company’s policy is to record a liability if a loss in a significant legal dispute is considered probable and an amount can be reasonably estimated. The Company provides disclosure when a loss in excess of any reserve is reasonably possible, and the Company is in a position to estimate the potential loss or range of possible loss. Significant judgment is required to assess the likelihood of various potential outcomes and the quantification of loss in those scenarios. The Company’s estimates change as litigation progresses and new information comes to light. Changes in Company estimates could have a material impact on the Company’s results and financial position.

Significant Agreements

Significant Agreements	6 Months Ended
	Jun. 30, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant Agreements	9. Significant Agreements Mitsubishi Tanabe Pharma Collaboration Agreement On December 11, 2015, the Company and Mitsubishi Tanabe Pharma Corporation, or MTPC, entered into a collaboration agreement (Collaboration Agreement) providing MTPC with exclusive development and commercialization rights to vadadustat (formerly known as AKB-6548), the Company’s product candidate for the treatment of anemia related to chronic kidney disease, in Japan and certain other Asian countries (collectively, the Territory). Pursuant to the Collaboration Agreement, MTPC will have an exclusive license to develop and commercialize vadadustat in the Territory. In addition, the Company will supply vadadustat for both clinical and commercial use in the Territory. The countries included in the Territory are Japan, Taiwan, South Korea, Singapore, Malaysia, India, Indonesia, East Timor, Mongolia, the Philippines, Vietnam, Laos, Cambodia, Thailand, Brunei, Myanmar, Nepal, Sri Lanka, Bangladesh, Bhutan, Maldives, Palau and Tonga. In consideration for the exclusive license and other rights contained in the Collaboration Agreement, MTPC will make payments totaling up to $100.0 million to fund the vadadustat global Phase 3 program, including $40.0 million paid in January 2016. If Japanese patients are not included in either the global Phase 3 PRO 2 2 The Company and MTPC will establish a joint steering committee to oversee development and commercialization of vadadustat in the Territory, including approval of any development or commercialization plans. Unless earlier terminated, the Collaboration Collaboration Collaboration As of June 30, 2016, there is $40.0 million of deferred revenue related to the Company’s Collaboration Agreement, all of which is classified as long‑term in the accompanying condensed consolidated balance sheet. Revenue recognition for the Collaboration Agreement will commence when all criteria as required under ASC 605 have been satisfied, which the Company expects will be in 2017 when the scope of the Phase 3 program is agreed upon with Japanese regulatory authorities.

Employee Retirement Plan

Employee Retirement Plan	6 Months Ended
	Jun. 30, 2016
Compensation And Retirement Disclosure [Abstract]
Employee Retirement Plan	10. Employee Retirement Plan During 2008, the Company established a retirement plan (the Plan) authorized by Section 401(k) of the Internal Revenue Code. In accordance with the Plan, all employees who have attained the age of 21 are eligible to participate in the Plan as of the first Entry Date, as defined, following their date of employment. Each employee can contribute a percentage of compensation up to a maximum of the statutory limits per year. Company contributions are discretionary and contributions in the amount of approximately $29,000 and $0 were made during the three months ended June 30, 2016 and 2015, respectively, and $0.1 million and $0 were made during the six months ended June 30, 2016 and 2015, respectively.

Net Loss per Share

Net Loss per Share	6 Months Ended
	Jun. 30, 2016
Earnings Per Share [Abstract]
Net Loss per Share	11. 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 Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 Outstanding stock options 2,753,908 1,975,620 2,753,908 1,975,620 Unvested restricted stock 159,640 295,206 159,640 295,206 Unvested restricted stock units 396,813 25,875 396,813 25,875 Total 3,310,361 2,296,701 3,310,361 2,296,701

Subsequent Event

Subsequent Event	6 Months Ended
	Jun. 30, 2016
Subsequent Events [Abstract]
Subsequent Event	12. Subsequent Event On July 25, 2016, the Company executed into a Third Amendment to Lease (Third Amendment), amending the lease dated December 3, 2013, for the Company’s headquarters located at 245 First Street, Cambridge, Massachusetts (the Building). Pursuant to the Third Amendment, the Company has agreed to extend its existing lease for approximately 5,951 rentable square feet of office, research and laboratory space located on the first floor of the science center in the Building (Lab Space). Monthly lease payments for the new space will be approximately $35,000 per month commencing approximately December 1, 2016, pending completion of work by the Landlord. The foregoing rent is subject to annual rent escalations commencing on December 1, 2017, depending on the date of delivery of the premises. The Third Amendment includes a Landlord’s contribution for leasehold improvements for the premises in the amount of $89,265. The term of the lease for the Lab Space is five years, with an extension option for one additional period of two years.

Summary of Significant Accoun18

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Basis of Presentation	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 U.S. GAAP as found in the Accounting Standards Codification (ASC) and Accounting Standards Update (ASU) of the Financial Accounting Standards Board (FASB). In the quarter ended December 31, 2015, the Company identified and corrected an error in the historical classification of certain operating costs between research and development and general and administrative expenses. The Company concluded the effect of this classification error was not material to its consolidated financial statements for any prior period. The classification correction had no effect on the Company’s current or historical total operating expenses or net loss. 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, 2015, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K (File No. 001-36352), which was filed with the Securities and Exchange Commission (SEC) on March 14, 2016.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard-setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting In February 2016, the FASB issued ASU 2016-02, Leases In August 2014, the FASB issued ASU 2014-15, which requires management of public and private companies to evaluate whether there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. If conditions or events raise substantial doubt about an entity’s ability to continue as a going concern, and substantial doubt is not alleviated after consideration of management’s plans, an entity should include a statement in the footnotes indicating that there is substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. The new standard is effective for annual periods ending after December 15, 2016, and for annual periods and interim periods thereafter. Early application is permitted. While the Company intends to adopt the standard as of December 31, 2016, if this standard had been adopted as of June 30, 2016, management of the Company believes that it would have concluded there is substantial doubt about the Company’s ability to continue as a going concern one year from the date of filing of this Form 10-Q. See Note 1 for additional information on our liquidity risks and management’s plans. In May 2014, the FASB issued a new revenue recognition standard which amends revenue recognition principles and provides a single, comprehensive set of criteria for revenue recognition within and across all industries. The new standard provides a five step framework whereby revenue is recognized when promised goods or services are transferred to a customer at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The standard also requires enhanced disclosures pertaining to revenue recognition in both interim and annual periods. In August 2015, the FASB deferred the effective date of the new revenue standard from January 1, 2017 to January 1, 2018. Early adoption is permitted any time after the original effective date, which for us is January 1, 2017. The standard allows for adoption using a full retrospective method or a modified retrospective method. The Company is currently evaluating the timing, method of adoption and the expected impact that the standard could have on our consolidated financial statements and related disclosures.
Segment Information	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	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: prepaid and accrued research and development expense, stock-based compensation expense, accrued expenses and income taxes. Prior to the initial public offering, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company granted stock options at exercise prices not less than the fair market value of its common stock as determined by the Board of Directors contemporaneously at the date such grants were made, with input from management. Prior to the Company’s initial public offering in March 2014, the fair value of common stock at the grant date was adjusted in connection with the Company’s retrospective fair value assessment for financial reporting purposes. Accordingly, the Board of Directors determined the estimated fair value of the Company’s common stock based on a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector and the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event, such as an initial public offering or sale of the Company.
Cash and Cash Equivalents	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 June 30, 2016, the Company’s cash is primarily in money market funds. The Company may maintain balances with its banks in excess of federally insured limits.
Investments	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 June 30, 2016. Unrealized losses on available-for-sale securities that are determined to be temporary, and not related to credit loss, are recorded in accumulated other comprehensive loss, a component of stockholders’ equity. The amortized cost of debt securities in this category reflects amortization of premiums and accretion of discounts to maturity computed under the effective interest method. The Company includes this amortization in the caption “Interest income” within the consolidated statements of operations and comprehensive loss. The Company also includes in net investment income, realized gains and losses and declines in value determined to be other than temporary. The Company bases the cost of securities sold upon the specific identification method, and includes interest and dividends on securities in interest income.
Revenue Recognition	Revenue Recognition To date, the Company has not generated any revenue from the sales of products or other means. For the foreseeable future, the Company expects substantially all of its revenues will be generated from its collaboration with Mitsubishi Tanabe (see Note 9) and any other collaborations the Company may enter into. The Company will recognize revenue in accordance with ASC Topic 605, Revenue Recognition · Persuasive evidence of an arrangement exists; · Delivery has occurred or services have been rendered; · The seller’s price to the buyer is fixed or determinable; and · Collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. The Company evaluates multiple‑element arrangements based on the guidance in ASC Topic 605‑25, Revenue Recognition Multiple‑Element Arrangements The consideration received under the arrangement that is fixed or determinable is then allocated among the separate units of accounting using the relative selling price method. The Company determines the estimated selling price for units of accounting within each arrangement using vendor‑specific objective evidence (VSOE) of selling price, if available, third‑party evidence (TPE) of selling price if VSOE is not available, or best estimate of selling price (BESP) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity‑specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company will recognize arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. In the event that a deliverable does not represent a separate unit of accounting, the Company will recognize revenue from the combined unit of accounting over the Company’s contractual or estimated performance period for the undelivered elements, which is typically the term of the Company’s research and development obligations. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company will recognize revenue under the arrangement on a straight‑line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue to be recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight‑line method or proportional performance method, as applicable, as of the period ending date. At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (1) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (2) the consideration relates solely to past performance and (3) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone and the level of effort and investment required to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are not considered substantive are recognized as earned if there are no remaining performance obligations or over the remaining period of performance, assuming all other revenue recognition criteria are met. Options are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the cost to exercise the option, the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option and the likelihood the option will be exercised. When an option is considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in allocable consideration, assuming the option is not priced at a significant and incremental discount. Conversely, when an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount would be included as a deliverable at the inception of the arrangement. The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met.
Patents	Patents Costs incurred in connection with the application for and issuance of patents are expensed as incurred.
Income Taxes	Income Taxes Income taxes are recorded in accordance with ASC Topic 740, Income Taxes 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 June 30, 2016 and 2015, the Company does not have any significant uncertain tax positions. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for its stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation Equity-Based Payments to Non-Employees The Black-Scholes option pricing model requires the input of certain subjective assumptions, including (a) the expected stock price volatility, (b) the calculation of expected term of the award, (c) the risk-free interest rate and (d) expected dividends. Due to the lack of company-specific historical and implied volatility data for trading the Company’s stock in the public market, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The computation of expected volatility is based on the historical volatility of a representative group of companies with similar characteristics to the Company, including stage of product development and life science industry focus. The Company is in the product development stage with no 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	Fair Value of Financial Instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. ASC Topic 820, Fair Value Measurements and Disclosures Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments, and is not a measure of the investment credit quality. The three levels of the fair value hierarchy are described below: · Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. · Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active, or for which all significant inputs are observable, either directly or indirectly. · Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Items measured at fair value on a recurring basis include short-term investments (see Note 4). The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The rate implicit within the Company’s capital lease obligation approximates market interest rates.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Cash and investments are the only financial instruments that potentially subject the Company to concentrations of credit risk. The Company maintains its cash with high quality, accredited financial institutions and, accordingly, such funds are subject to minimal credit risk. The Company has no significant off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.
Net Loss per Share	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 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 June 30, 2016 and December 31, 2015. Useful Life June 30, 2016 December 31, 2015 (in thousands) Computer equipment and software 3 $ 618 $ 300 Furniture and fixtures 5 475 243 Equipment 7 50 50 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 878 70 Office equipment under capital lease 3 36 24 2,057 687 Less accumulated depreciation (225 ) (147 ) Net property and equipment $ 1,832 $ 540 Depreciation expense, including expense associated with assets under capital leases, was approximately $46,000 and $32,000 for the three months ended June 30, 2016 and 2015, respectively and $78,000 and $50,000 for the six months ended June 30, 2016 and 2015, respectively.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2016
Accounting Policies [Abstract]
Summary of Equipment and Related Accumulated Depreciation	The following is the summary of property and equipment and related accumulated depreciation as of June 30, 2016 and December 31, 2015. Useful Life June 30, 2016 December 31, 2015 (in thousands) Computer equipment and software 3 $ 618 $ 300 Furniture and fixtures 5 475 243 Equipment 7 50 50 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 878 70 Office equipment under capital lease 3 36 24 2,057 687 Less accumulated depreciation (225 ) (147 ) Net property and equipment $ 1,832 $ 540

Available for Sale Securities (

Available for Sale Securities (Tables)	6 Months Ended
	Jun. 30, 2016
Investments Debt And Equity Securities [Abstract]
Summary of Available for Sale Securities at Fair Value	Available for sale securities at June 30, 2016 and December 31, 2015 consist of the following : Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) June 30, 2016 Cash and cash equivalents $ 46,177 $ — $ — $ 46,177 Available for sale securities: Certificates of deposit $ 19,063 — — $ 19,063 U.S. Government debt securities 111,004 38 (5 ) 111,037 Corporate debt securities 12,368 5 (1 ) 12,372 Total available for sale securities $ 142,435 $ 43 $ (6 ) $ 142,472 Total cash, cash equivalents, and available for sale securities $ 188,612 $ 43 $ (6 ) $ 188,649 Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) December 31, 2015 Cash and cash equivalents $ 49,778 $ — $ — $ 49,778 Available for sale securities: Certificates of deposit $ 21,505 — — $ 21,505 U.S. Government debt securities 46,461 — (185 ) 46,276 Corporate debt securities 20,944 1 (50 ) 20,895 Total available for sale securities $ 88,910 $ 1 $ (235 ) $ 88,676 Total cash, cash equivalents, and available for sale securities $ 138,688 $ 1 $ (235 ) $ 138,454
Estimated Fair Value of Available for Sale Securities at Fair Value by Contractual Maturity	The estimated fair value of the Company’s available for sale securities balance at June 30, 2016, by contractual maturity, is as follows: Due in one year or less $ 114,894 Due after one year 27,578 Total available for sale securities $ 142,472

Fair Value of Financial Instr21

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Assets Measured or Disclosed at Fair Value on Recurring Basis	Assets measured or disclosed at fair value on a recurring basis as of June 30, 2016 and December 31, 2015 are summarized below: Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) June 30, 2016 Assets: Cash and cash equivalents $ 46,177 $ — $ — $ 46,177 Certificates of deposit — 19,063 — 19,063 U.S. Government debt securities — 111,037 — 111,037 Corporate debt securities — 12,372 — 12,372 $ 46,177 $ 142,472 $ — $ 188,649 Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) December 31, 2015 Assets: Cash and cash equivalents $ 49,778 $ — $ — $ 49,778 Certificates of deposit — 21,505 — 21,505 U.S. Government debt securities — 46,276 — 46,276 Corporate debt securities — 20,895 — 20,895 $ 49,778 $ 88,676 $ — $ 138,454

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2016
Payables And Accruals [Abstract]
Components of Accrued Expenses	Accrued expenses are as follows: June 30, 2016 December 31, 2015 (in thousands) Accrued clinical $ 10,692 $ 4,536 Accrued bonus 1,250 2,178 Professional fees 761 647 Accrued vacation 433 310 Accrued payroll 410 518 Accrued severance 196 — Other 2,047 1,366 Total accrued expenses $ 15,789 $ 9,555

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2016
Equity [Abstract]
Summary of Reserved Shares of Common Stock for Future Issuance	The Company has reserved for future issuance the following number of shares of common stock: June 30, 2016 December 31, 2015 Unvested restricted common stock 159,640 216,716 Common stock options and RSU's outstanding 3,150,718 2,231,057 Shares available for issuance under the 2014 Plan (1) 1,305,784 1,318,732 Shares available for issuance under the ESPP (2) 803,105 440,304 Total 5,419,247 4,206,809 (1) On January 1, 2016, the shares reserved for future grants under the 2014 Plan increased by 986,800 shares pursuant to the 2014 Plan Evergreen Provision. (2) On February 28, 2016, the shares reserved for future issuance under the ESPP increased by 379,430 shares pursuant to the ESPP Evergreen Provision.
Compensation Cost Related to Share-Based Awards	The Company has recognized the following compensation cost related to share-based awards: Three Months Ended Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 (in thousands) (in thousands) Research and development $ 365 $ 397 $ 757 $ 962 General and administrative 857 698 1,716 1,261 Total $ 1,222 $ 1,095 $ 2,473 $ 2,223
Schedule of Compensation Expense by Type of Award	Compensation expense by type of award: Three Months Ended Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 (in thousands) (in thousands) Stock options $ 1,021 $ 908 $ 2,149 $ 1,607 Restricted stock 27 142 13 542 Restricted stock units 158 24 264 32 Employee stock purchase plan 16 21 47 42 Total $ 1,222 $ 1,095 $ 2,473 $ 2,223

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments Required Under Leases	At June 30, 2016, the Company’s future minimum payments required under these leases are as follows: Operating Capital Lease Lease Total (in thousands) 2016 $ 1,425 $ 6 $ 1,431 2017 3,117 9 3,126 2018 3,117 5 3,122 2019 3,117 — 3,117 2020 3,117 — 3,117 Thereafter 17,664 — 17,664 Total $ 31,557 20 $ 31,577 Less amount representing interest (1 ) Present value of minimum lease payments at June 30, 2016 $ 19

Net Loss per Share (Tables)

Net Loss per Share (Tables)	6 Months Ended
	Jun. 30, 2016
Earnings Per Share [Abstract]
Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share	The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect: Three Months Ended Six Months Ended June 30, 2016 June 30, 2015 June 30, 2016 June 30, 2015 Outstanding stock options 2,753,908 1,975,620 2,753,908 1,975,620 Unvested restricted stock 159,640 295,206 159,640 295,206 Unvested restricted stock units 396,813 25,875 396,813 25,875 Total 3,310,361 2,296,701 3,310,361 2,296,701

Nature of Organization and Op26

Nature of Organization and Operations - Additional Information (Details)	Dec. 11, 2015USD ($)	May 31, 2016USD ($)	Jan. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)	Jun. 30, 2016USD ($)shares	Jun. 30, 2016USD ($)Patient	Jun. 30, 2016USD ($)Underwritten_offering
Nature Of Organization And Operations [Line Items]
Cash and cash equivalents and available for sale securities				$ 138,454,000	$ 188,649,000	$ 188,649,000	$ 188,649,000
Cash and cash equivalents					188,600,000	188,600,000	188,600,000
Current accounts payable and accrued expenses					$ 20,900,000	$ 20,900,000	20,900,000
Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares | shares					0
IPO
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of initial public offering							$ 187,400,000
Number of underwritten public offerings | Underwritten_offering							3
Follow-on public offering
Nature Of Organization And Operations [Line Items]
Proceeds from issuance of initial public offering			$ 61,000,000
Sale of stock, price per share | $ / shares			$ 9
Follow-on public offering | Common Stock
Nature Of Organization And Operations [Line Items]
Issuance of common stock, shares | shares			7,250,000
Minimum
Nature Of Organization And Operations [Line Items]
Expected to incur substantial losses (in years)						4 years
Maximum
Nature Of Organization And Operations [Line Items]
Expected to incur substantial losses (in years)						5 years
Maximum | Cantor Fitzgerald & Co
Nature Of Organization And Operations [Line Items]
Common stock sales agreement amount		$ 75,000,000
Phase 3 vadadustat program | Minimum
Nature Of Organization And Operations [Line Items]
Cost of program per patient						$ 80,000
Phase 3 vadadustat program | Maximum
Nature Of Organization And Operations [Line Items]
Cost of program per patient						$ 85,000
PRO2TECT
Nature Of Organization And Operations [Line Items]
Number of patients | Patient						3,100
INNO2VATE
Nature Of Organization And Operations [Line Items]
Number of patients | Patient						2,600
Development and Commercialize Collaboration Agreement
Nature Of Organization And Operations [Line Items]
Collaborative arrangement right description						In December 2015, the Company entered into a collaboration agreement with Mitsubishi Tanabe to develop and commercialize vadadustat in Japan and certain other countries in Asia for total milestone payments of up to $350.0 million, including up to $100.0 million in upfront and development payments, of which $40.0 million was received in January 2016. If Japanese patients are not included in either the global Phase 3 PRO2TECT or INNO2VATE programs, $20.0 million of the $40.0 million received would be used to fund further local development of vadadustat in Japan or be refunded to Mitsubishi. In addition, the Company will receive tiered double-digit royalty payments on sales of vadadustat.
Development and Commercialize Collaboration Agreement | Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue			$ 40,000,000
Milestone revenue refundable			$ 20,000,000
Development and Commercialize Collaboration Agreement | Maximum
Nature Of Organization And Operations [Line Items]
Milestone revenue				350,000,000
Development and Commercialize Collaboration Agreement | Maximum | Upfront
Nature Of Organization And Operations [Line Items]
Milestone revenue	$ 100,000,000			$ 100,000,000

Summary of Significant Accoun27

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2016USD ($)Segment	Jun. 30, 2015USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment			1
Significant uncertain tax positions	$ 0	$ 0	$ 0	$ 0
Revenue			$ 0
Expected dividend yield			0.00%
Depreciation expense	$ 46,000	$ 32,000	$ 78,000	$ 50,000
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property, plant and equipment, Useful life			7 years

Summary of Significant Accoun28

Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 2,057	$ 687
Less accumulated depreciation	(225)	(147)
Net property and equipment	$ 1,832	540
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 618	300
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	$ 475	243
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	$ 50	50
Leasehold improvements
Property, Plant and Equipment [Line Items]
Leasehold improvements, Useful Life	Shorter of the useful life or remaining lease term (10 years)
Gross property, plant and equipment	$ 878	70
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	10 years
Office equipment under capital lease
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 36	$ 24

Available for Sale Securities -

Available for Sale Securities - Summary of Available for Sale Securities at Fair Value (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 142,435	$ 88,910
Gross Unrealized Gains	43	1
Gross Unrealized Losses	(6)	(235)
Fair Value	142,472	88,676
Cash and cash equivalents	46,177	49,778	$ 76,248	$ 32,780
Cash and cash equivalents, fair value	46,177	49,778
Total cash, cash equivalents, and available for sale securities - Amortized Cost	188,612	138,688
Cash and cash equivalents and available for sale securities	188,649	138,454
U.S. Government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	111,004	46,461
Gross Unrealized Gains	38
Gross Unrealized Losses	(5)	(185)
Fair Value	111,037	46,276
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,063	21,505
Fair Value	19,063	21,505
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	12,368	20,944
Gross Unrealized Gains	5	1
Gross Unrealized Losses	(1)	(50)
Fair Value	$ 12,372	$ 20,895

Available for Sale Securities30

Available for Sale Securities - Estimated Fair Value of Available for Sale Securities by Contractual Maturity (Details) $ in Thousands	Jun. 30, 2016USD ($)
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 114,894
Due after one year	27,578
Total available for sale securities	$ 142,472

Fair Value of Financial Instr31

Fair Value of Financial Instruments - Assets Measured or Disclosed at Fair Value on Recurring Basis (Detail) - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 0	$ 0
Fair value measurements recurring
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	188,649,000	138,454,000
Fair value measurements recurring | U.S. Government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	111,037,000	46,276,000
Fair value measurements recurring | Cash and cash equivalents
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	46,177,000	49,778,000
Fair value measurements recurring | Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	19,063,000	21,505,000
Fair value measurements recurring | Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	12,372,000	20,895,000
Fair value measurements recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	46,177,000	49,778,000
Fair value measurements recurring | Level 1 | 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	46,177,000	49,778,000
Fair value measurements recurring | Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	142,472,000	88,676,000
Fair value measurements recurring | Level 2 | U.S. Government debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	111,037,000	46,276,000
Fair value measurements recurring | Level 2 | Certificates of deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	19,063,000	21,505,000
Fair value measurements recurring | Level 2 | Corporate debt securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 12,372,000	$ 20,895,000

Fair Value of Financial Instr32

Fair Value of Financial Instruments - Additional Information (Detail) - Level 3 - USD ($)	Jun. 30, 2016	Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets Measured at fair value on recurring basis	$ 0	$ 0
Liabilities measured at fair value on recurring basis	$ 0	$ 0

Accrued Expenses - Components o

Accrued Expenses - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued clinical	$ 10,692	$ 4,536
Accrued bonus	1,250	2,178
Professional fees	761	647
Accrued vacation	433	310
Accrued payroll	410	518
Accrued severance	196
Other	2,047	1,366
Total accrued expenses	$ 15,789	$ 9,555

Accrued Expenses - Additional I

Accrued Expenses - Additional Information (Details) - Separation Agreement 2 $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2016Employee	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Jun. 30, 2016USD ($)
Accrued Expenses [Line Items]
Severance expense			$ 0.4
Payment out of severance accrual		$ 0.1		$ 0.2
Number of employees | Employee	2
Severance agreement description				In January 2016, the Company entered into separation agreements with two employees. During the first quarter of 2016, the Company recorded severance expense in the amount of $0.4 million, of which $0.2 million was recorded to general and administrative expense and $0.2 million was recorded to research and development expense. During the three months ended June 30, 2016, approximately $0.1 million was paid out of the severance accrual and during the six months ended June 30, 2016, approximately $0.2 was paid out of the severance accrual.
General and Administrative Expense
Accrued Expenses [Line Items]
Severance expense			0.2
Research and Development Expense
Accrued Expenses [Line Items]
Severance expense			$ 0.2

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	Feb. 22, 2016	Dec. 23, 2013	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares authorized			175,000,000		175,000,000		175,000,000	175,000,000
Common stock, par value			$ 0.00001		$ 0.00001		$ 0.00001	$ 0.00001
Common stock, shares issued			38,008,933		38,008,933		30,662,218
Common stock, shares outstanding			38,008,933		38,008,933		30,662,218
Preferred stock, shares authorized			25,000,000		25,000,000		25,000,000
Preferred stock, par value			$ 0.00001		$ 0.00001		$ 0.00001
Preferred stock, shares issued			0		0		0
Preferred stock, shares outstanding			0		0		0
Common stock, shares reserved for future issuance			5,419,247		5,419,247		4,206,809
Stock-based compensation expense			$ 1,222,000	$ 1,095,000	$ 2,473,000	$ 2,223,000
Restricted Stock Units
Class of Stock [Line Items]
Vesting periods					3 years
Stock-based compensation expense			158,000	24,000	$ 264,000	32,000
Total compensation cost to be recognized			2,900,000		$ 2,900,000
Restricted Stock Units | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage					100.00%
Stock Options
Class of Stock [Line Items]
Shares issued	624,275
Stock-based compensation description					Options vest in installments of (i) 25% at the one year anniversary and (ii) in either 36 or 48 equal monthly or 12 equal quarterly installments beginning in the thirteenth month after the initial Vesting Commencement Date (as defined) or grant date, subject to the employee’s continuous service with the Company
Options expiration after the date of grant					10 years
Stock-based compensation expense			$ 1,021,000	908,000	$ 2,149,000	1,607,000
Stock Options | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage					25.00%
Restricted Stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance			159,640		159,640		216,716
Vesting periods		1 year
Stock-based compensation expense			$ 27,000	$ 142,000	$ 13,000	$ 542,000
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
Restricted Stock | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage		25.00%
Restricted Stock | Employees
Class of Stock [Line Items]
Granted, Shares		450,224
Restricted Stock | Non Employees
Class of Stock [Line Items]
Granted, Shares		79,067
Stock-based compensation expense			$ 27,000
Maximum | Stock Options
Class of Stock [Line Items]
Vesting periods					48 months
Minimum | Stock Options
Class of Stock [Line Items]
Vesting periods					12 months
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance			1,305,784		1,305,784		1,318,732		1,785,000
Incremental rate at which the shares reserved for issuance increase					3.00%
2014 Plans | Employees
Class of Stock [Line Items]
Granted, Shares					849,275
2014 Plans | Director
Class of Stock [Line Items]
Granted, Shares					87,500
2014 Plans | Restricted Stock Units
Class of Stock [Line Items]
Granted, Shares					402,338
2014 Plans | Maximum
Class of Stock [Line Items]
Common stock, shares reserved for future issuance			1,131,937		1,131,937
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued			262,500		262,500
Percentage of increase on common stock authorized on each anniversary					1.00%
Number of common stock outstanding					739,611
Common stock shares authorized percentage under the plan					5.00%
Purchase price at the end of offering period					85.00%
Offering period					6 months
Shares issued			16,629
Stock-based compensation expense			$ 16,000		$ 47,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Jun. 30, 2016	Dec. 31, 2015	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	5,419,247	4,206,809
Restricted Stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	159,640	216,716
Stock Options and Restricted Stock Units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	3,150,718	2,231,057
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	803,105	440,304
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	1,305,784	1,318,732	1,785,000

Stockholders' Equity - Summar37

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

Stockholders Equity - Compensat

Stockholders Equity - Compensation Cost Related to Share-Based Awards (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,222	$ 1,095	$ 2,473	$ 2,223
Research and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	365	397	757	962
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 857	$ 698	$ 1,716	$ 1,261

Stockholders Equity - Schedule

Stockholders Equity - Schedule of Compensation Expense by Type of Award (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,222,000	$ 1,095,000	$ 2,473,000	$ 2,223,000
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,021,000	908,000	2,149,000	1,607,000
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	27,000	142,000	13,000	542,000
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	158,000	24,000	264,000	32,000
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 16,000	$ 21,000	$ 47,000	$ 42,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income tax provisions or benefits	$ 0	$ 0	$ 0	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	Nov. 30, 2015USD ($)ft²	Dec. 31, 2014USD ($)ft²	Dec. 31, 2013USD ($)ft²	Jun. 30, 2016USD ($)ft²	Jun. 30, 2015USD ($)	Jun. 30, 2016USD ($)ft²	Jun. 30, 2015USD ($)	Dec. 31, 2015USD ($)
Commitments And Contingencies [Line Items]
Lease period			3 years
Area of property leased | ft²		8,530	6,837
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
Lease space occupancy date		Mar. 13, 2015
Lease expiration date						Dec. 31, 2016
Landlord contribution for leasehold improvements		$ 100,000
Additional cash security deposit paid to landlord		$ 179,130
Rent expense associated with lease				$ 700,000	$ 200,000	$ 1,000,000	$ 400,000
Contract cost incurred in research and development activities						13,900,000		$ 5,200,000
Total remaining contract costs				443,200,000		$ 443,200,000
Office Equipment One
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2014-02
Office Equipment Two
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2015-04
Office Equipment Three
Commitments And Contingencies [Line Items]
Capital leases term						3 years
Capital lease commencement period						2016-02
Second Amendment
Commitments And Contingencies [Line Items]
Lease period						10 years
Area of property leased | ft²	23,189
Monthly lease payments	$ 107,000
Lease expiration date						Aug. 31, 2026
Additional cash security deposit paid to landlord	$ 976,382
Square feet of leased property | ft²	16,222
Operating lease payments commencement date						May 1, 2017
Second Amendment | Other Assets
Commitments And Contingencies [Line Items]
Additional cash security deposit paid to landlord				$ 1,280,857		$ 1,280,857		$ 304,475
Second Amendment | Delivered on December 31, 2015
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 20,000
Square feet of leased property | ft²				3,066		3,066
Operating lease payments commencement date						Apr. 1, 2016
Second Amendment | Delivered on April 11, 2016
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 110,000
Square feet of leased property | ft²				16,739		16,739
Operating lease payments commencement date						Sep. 11, 2016
Second Amendment | Delivered on January 1, 2017
Commitments And Contingencies [Line Items]
Monthly lease payments						$ 23,000
Square feet of leased property | ft²				3,384		3,384
Operating lease payments commencement date						May 1, 2017

Commitments and Contingencies42

Commitments and Contingencies - Schedule of Future Minimum Payments Required Under Leases (Details) $ in Thousands	Jun. 30, 2016USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2016	$ 1,425
Operating Lease, 2017	3,117
Operating Lease, 2018	3,117
Operating Lease, 2019	3,117
Operating Lease, 2020	3,117
Operating Lease, Thereafter	17,664
Operating Lease, Total	31,557
Capital Lease, 2016	6
Capital Lease, 2017	9
Capital Lease, 2018	5
Capital Lease, Total	20
Capital Lease, Less amount representing interest	(1)
Capital Lease, Present value of minimum lease payments at June 30, 2016	19
Operating and Capital Lease, 2016	1,431
Operating and Capital Lease, 2017	3,126
Operating and Capital Lease, 2018	3,122
Operating and Capital Lease, 2019	3,117
Operating and Capital Lease, 2020	3,117
Operating and Capital Lease, Thereafter	17,664
Operating and Capital Lease, Total	$ 31,577

Significant Agreements - Additi

Significant Agreements - Additional Information (Details) - USD ($)	Dec. 11, 2015	Jan. 31, 2016	Dec. 31, 2015	Jun. 30, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, noncurrent				$ 40,000,000
Development and Commercialize Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum percentage of royalty payments	20.00%
Collaboration Agreement, expiration period	10 years
Collaboration Agreement, notice period for termination	12 months
Deferred revenue, noncurrent				$ 40,000,000
Development and Commercialize Collaboration Agreement | Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue		$ 40,000,000
Milestone revenue refundable		$ 20,000,000
Development and Commercialize Collaboration Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue			$ 350,000,000
Development and Commercialize Collaboration Agreement | Maximum | Upfront
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue	$ 100,000,000		$ 100,000,000
Development and Commercialize Collaboration Agreement | Maximum | Additional Milestone Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone revenue	$ 250,000,000

Employee Retirement Plan - Addi

Employee Retirement Plan - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Compensation And Retirement Disclosure [Abstract]
Employers contributions to defined contribution plan	$ 29,000	$ 0	$ 100,000	$ 0
Employees eligibility age to participate in retirement plan			21 years

Net Loss per Share - Anti-Dilut

Net Loss per Share - Anti-Dilutive Securities Excluded from Calculation of Diluted Net Loss per Share (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,310,361	2,296,701	3,310,361	2,296,701
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	2,753,908	1,975,620	2,753,908	1,975,620
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	159,640	295,206	159,640	295,206
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	396,813	25,875	396,813	25,875

Subsequent Event - Additional I

Subsequent Event - Additional Information (Details)	Jul. 25, 2016USD ($)ft²Extension_Option	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Jun. 30, 2016USD ($)
Subsequent Event [Line Items]
Monthly lease payments		$ 45,000	$ 31,000	$ 32,000
Landlord contribution for leasehold improvements		$ 100,000
Subsequent Event | Third Amendment | Lab Space
Subsequent Event [Line Items]
Square feet of leased property | ft²	5,951
Monthly lease payments	$ 35,000
Operating lease payments commencement date	Dec. 1, 2016
Landlord contribution for leasehold improvements	$ 89,265
Lease period	5 years
Lease period, number of extension options | Extension_Option	1
Lease extension period	2 years