Akebia Therapeutics (AKBA) 10-Q 8 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
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 Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		57,059,063

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 162,430	$ 70,156
Available for sale securities	227,714	247,636
Accounts receivable	688	34,216
Prepaid expenses and other current assets	6,694	6,348
Total current assets	397,526	358,356
Property and equipment, net	3,808	3,617
Other assets	2,492	2,274
Total assets	403,826	364,247
Current liabilities:
Accounts payable	12,684	6,998
Accrued expenses	94,616	52,441
Short-term deferred revenue	70,099	81,667
Total current liabilities	177,399	141,106
Deferred rent, net of current portion	2,421	2,588
Deferred revenue, net of current portion	81,424	97,957
Other non-current liabilities	41	22
Total liabilities	261,285	241,673
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock $0.00001 par value, 25,000,000 shares authorized; 0 shares issued and outstanding at September 30, 2018 and December 31, 2017
Common stock: $0.00001 par value; 175,000,000 shares authorized at September 30, 2018 and December 31, 2017; 57,046,563 and 47,612,619 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	1	0
Additional paid-in capital	597,290	493,823
Accumulated other comprehensive loss	(409)	(442)
Accumulated deficit	(454,341)	(370,807)
Total stockholders' equity	142,541	122,574
Total liabilities and stockholders' equity	$ 403,826	$ 364,247

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
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	57,046,563	47,612,619
Common stock, shares outstanding	57,046,563	47,612,619

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Collaboration revenue	$ 53,169	$ 41,283	$ 147,892	$ 90,668
Type of revenue [extensible list]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 70,634	$ 58,711	$ 203,955	$ 162,511
General and administrative	10,378	6,748	31,940	19,441
Total operating expenses	81,012	65,459	235,895	181,952
Operating loss	(27,843)	(24,176)	(88,003)	(91,284)
Other income:
Interest income	1,780	842	4,417	1,886
Other income	16	200	52	204
Net loss	$ (26,047)	$ (23,134)	$ (83,534)	$ (89,194)
Net loss per share - basic and diluted	$ (0.46)	$ (0.49)	$ (1.54)	$ (2.11)
Weighted-average number of common shares - basic and diluted	57,027,598	46,938,618	54,207,973	42,202,560
Comprehensive loss:
Net loss	$ (26,047)	$ (23,134)	$ (83,534)	$ (89,194)
Other comprehensive gain (loss) - unrealized gain (loss) on debt securities	50	73	33	(181)
Total comprehensive loss	$ (25,997)	$ (23,061)	$ (83,501)	$ (89,375)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net loss	$ (83,534)	$ (89,194)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	638	420
Amortization of premium/discount on investments	(698)	543
Stock-based compensation	6,978	6,674
Fair value of warrants issued for license		3,413
Changes in operating assets and liabilities:
Accounts receivable	33,528	33,542
Prepaid expenses and other current assets	(346)	(1,797)
Other long-term assets	67	(4)
Accounts payable	5,686	6,666
Accrued expense	42,118	(8,834)
Deferred revenue	(28,101)	8,443
Deferred rent	(131)	347
Net cash used in operating activities	(23,795)	(39,781)
Investing activities:
Purchase of equipment	(776)	(1,172)
Proceeds from the maturities of available for sale securities	180,091	97,868
Proceeds from sales of available for sale securities	13,000
Purchase of available for sale securities	(172,438)	(265,648)
Net cash provided by (used in) investing activities	19,877	(168,952)
Financing activities:
Proceeds from the issuance of common stock, net of issuance costs	95,453	109,541
Proceeds from the sale of stock under employee stock purchase plan	482	352
Proceeds from the exercise of stock options	555	1,108
Payments on capital lease obligations	(13)	(4)
Net cash provided by financing activities	96,477	110,997
Increase (decrease) in cash, cash equivalents, and restricted cash	92,559	(97,736)
Cash, cash equivalents, and restricted cash at beginning of the period	71,437	188,616
Cash, cash equivalents, and restricted cash at end of the period	$ 163,996	$ 90,880

Nature of Organization and Oper

Nature of Organization and Operations	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Nature of Organization and Operations	1. Nature of Organization and Operations The Company is a biopharmaceutical company focused on developing and commercializing novel therapeutics for patients based on hypoxia-inducible factor, or HIF, biology, and building its pipeline while leveraging its development and commercial expertise in renal disease. HIF is the primary regulator of the production of red blood cells in the body, as well as other important metabolic functions. Pharmacologic modulation of the HIF pathway may have broad therapeutic applications. The Company’s lead product candidate, vadadustat, is an oral therapy in Phase 3 development, and has the potential to set a new standard of care in the treatment of anemia due to chronic kidney disease, or CKD. The Company’s management team has extensive experience in developing and commercializing drugs for the treatment of renal and metabolic disorders, as well as a deep understanding of HIF biology. This unique combination of HIF and renal expertise is enabling the Company to advance a pipeline of HIF-based therapies to potentially address serious diseases. Since inception, the Company has devoted most of its resources to research and development, including its preclinical and clinical development activities, raising capital, and providing general and administrative support. The Company’s product candidates are subject to long development cycles, and the Company may be unsuccessful in its efforts to develop, obtain marketing approval for or market its product candidates. The Company has not generated any product revenue to date and may never generate any product revenue in the future. The Company believes that its existing cash, cash equivalents, and available for sale securities of approximately $390.1 million at September 30, 2018, together with the committed funding from its collaboration partners, will be sufficient to allow the Company to fund its current operating plan through the first quarter of 2020 and, as a result, through at least twelve months from the filing of the Company’s Quarterly Report on Form 10-Q for the quarterly period ended September 30, 2018. There can be no assurance, however, that the current operating plan will be achieved in the time frame anticipated by the Company, or that its cash resources will fund the Company’s operating plan for the period anticipated by the Company. The Company will require additional capital for the further development of its existing product candidates and will need to raise additional funds to pursue development activities related to additional product candidates; however, there can be no assurances that additional funding will be available on terms acceptable to the Company, or at all. If and until the Company can generate a sufficient amount of revenue from its products, it expects to finance future cash needs through public or private equity or debt offerings, payments from its collaborators, strategic transactions, or a combination of these approaches. On June 28, 2018, the Company entered into an Agreement and Plan of Merger, which was amended on October 1, 2018, or the Merger Agreement, with Keryx Biopharmaceuticals, Inc., or Keryx, and Alpha Therapeutics Merger Sub, Inc., a direct, wholly owned subsidiary of the Company, or the Merger Sub., pursuant to which the Merger Sub shall be merged with and into Keryx, with Keryx surviving as a wholly owned subsidiary of the Company, subject to the satisfaction or waiver of the conditions specified in the Merger Agreement, or the Merger. Subject to the terms and conditions of the Merger Agreement, at the effective time of the Merger, each share of common stock of Keryx issued and outstanding immediately prior to the effective time of the Merger will be cancelled and converted into the right to receive 0.37433, or the Exchange Multiplier, fully paid and non-assessable shares of common stock of the Company. The Merger Agreement also provides that at the effective time of the Merger, each share of Keryx common stock that is subject to an outstanding Keryx restricted stock award issued under a Keryx equity plan, or Keryx Restricted Shares, other than those Keryx Restricted Shares that accelerate or lapse as a result of the completion of the Merger, will convert into restricted stock unit awards, or RSUs, of the Company, the number of which will be adjusted in accordance with the Exchange Multiplier, and in accordance with the terms of the Merger Agreement. In addition, each outstanding and unexercised option to acquire Keryx common stock granted under the Keryx equity plan will be converted into an option to acquire shares of the Company’s common stock, with the number of shares and exercise price adjusted by the Exchange Multiplier, in accordance with the terms of the Merger Agreement. The foregoing exchange is expected to result in implied equity ownership in the combined company of 49.4 percent for the Company shareholders and 50.6 percent for Keryx shareholders on a fully-diluted basis, calculated based on the companies’ fully diluted market capitalizations as of the date of signing of the Merger Agreement and also taking into account the 4,000,000 additional shares of Keryx common stock that are expected to be issued to Keryx’s significant shareholder, Baupost Group Securities, L.L.C., or Baupost, prior to consummation of the Merger, as described below. The Merger is expected to be completed by the end of 2018 and is subject to the satisfaction of customary closing conditions including, among other things, (i) approval by the affirmative vote of the holders of a majority of the votes cast affirmatively or negatively, at the Company’s shareholders’ meeting in favor of the issuance of Company common stock in connection with the Merger, (ii) the adoption of the Merger Agreement by the affirmative vote of the holders of a majority of all outstanding shares of Keryx common stock entitled to vote thereon and (iii) the expiration or termination of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, which waiting period was terminated by the Federal Trade Commission on August 21, 2018. The Company’s obligation to consummate the Merger is also subject to the conversion of Keryx’s Zero Coupon Convertible Senior Notes due 2021, or Senior Notes, pursuant to the terms of the Notes Conversion Agreement entered into by the Company, Keryx and Baupost. The Merger Agreement provides for certain termination rights for both the Company and Keryx. Upon termination of the Merger under certain specified circumstances, the Company or Keryx may be required to pay the other party a termination fee of $22.0 million. Keryx, headquartered in Boston, Massachusetts, is focused on the development and commercialization of medicines for people with kidney disease. Keryx’s proprietary product, Auryxia ® Simultaneously with the execution of the Merger Agreement, the Company entered into a Voting Agreement with Baupost and the Notes Conversion Agreement with Baupost and Keryx. Pursuant to the Voting Agreement, Baupost agreed, among other things, to vote its shares in favor of the adoption of the Merger Agreement and against any alternative proposal and against approval of any proposal made in opposition to, in competition with, or inconsistent with, the Merger Agreement or the Merger or any other transactions contemplated by the Merger Agreement. Pursuant to the Notes Conversion Agreement, Baupost agreed to convert Keryx’s Senior Notes into 35,582,335 shares of Keryx common stock in accordance with the terms of the governing indenture immediately prior to the effective time of the Merger, conditioned upon the issuance to Baupost of an additional 4,000,000 shares of Keryx common stock. The Notes Conversion Agreement provides that the Company will execute a registration rights agreement with Baupost, to provide customary registration rights for any shares of Company common stock held by Baupost if and when the Merger is consummated.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP, for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. 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, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB. In the opinion of management, all adjustments, consisting of normal recurring accruals and revisions of estimates, considered necessary for a fair presentation of the unaudited condensed consolidated financial statements have been included. Certain amounts in the prior period financial statements have been revised to conform to the presentation of the current period financial statements. See “New Accounting Pronouncements – Recently Adopted” below for a discussion of certain revisions to prior period financial statements made in connection with the Company’s adoption of new revenue recognition guidance retroactive to January 1, 2016. Otherwise, these reclassifications had no significant effects on the previously reported net loss. Interim results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2018 or any other future period. The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Akebia Therapeutics Securities Corporation, Akebia Europe Limited and the Merger Sub. All intercompany balances and transactions have been eliminated in consolidation. Management has determined that the Company operates in one segment, which is the business of developing and commercializing proprietary therapeutics based on HIF biology. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the Securities and Exchange Commission on March 12, 2018, or the 2017 Annual Report on Form 10-K. The significant accounting policies used in preparation of these unaudited condensed consolidated financial statements for the three and nine months ended September 30, 2018 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s 2017 Annual Report on Form 10-K and are updated below as necessary. New Accounting Pronouncements – Recently Adopted In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition • For all reporting periods presented before January 1, 2018, the Company has not disclosed the amount of the transaction price allocated to the remaining performance obligations or an explanation of when the Company expects to recognize the amount as revenue. • The Company has not adjusted the promised amount of consideration for the effects of a significant financing component when the Company expects, at contract inception, that the period between when the entity transfers a promised good or a service to a customer and when the customer pays for that good or service will be one year or less. • The Company recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is one year or less. The Company, as a result of adopting ASC 606 on January 1, 2018, has revised its comparative financial statements for the prior year as if ASC 606 had been effective for that period, as set forth below. No changes for the adoption of ASC 606 were deemed necessary for the year ended December 31, 2016 and applicable interim periods within the year. With respect to the collaboration agreements with Otsuka Pharmaceutical Co. Ltd., or Otsuka, and Mitsubishi Tanabe Pharma Corporation, or MTPC, the Company concluded that there was no impact to revenue for the three and nine months ended September 30, 2017 after the adoption of ASC 606. As a result, there is no change to the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2017. The changes shown in the table below relate to the Company’s collaboration agreement with MTPC and the impact of when milestone payments can be recognized under the new standard as well as the period over which this revenue is recognized. Under ASC 605-28, Revenue Recognition-Milestone Method December 31, 2017 (in thousands) As revised under ASC 606 As originally reported under ASC 605 Effect of change Short-term deferred revenue $ 81,667 $ 84,910 $ (3,243 ) Accumulated deficit $ (370,807 ) $ (374,050 ) $ 3,243 In October 2016, the FASB issued ASU 2016-18, Restricted Cash , which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally describes as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, and interim periods within those years, using a retrospective transition method to each period presented, with early adoption permitted. The ASU requires the application of a retrospective transition method to each period presented. The Company elected to adopt this ASU effective January 1, 2018. The adoption of this guidance resulted in the relocation of $1.3 million in restricted cash from cash used in operating activities to cash, cash equivalents, and restricted cash at the beginning of the period in the unaudited condensed consolidated statement of cash flows for each of the nine months ended September 30, 2018 and 2017. New Accounting Pronouncements – Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes, and management must select an amount that falls within that range of reasonable estimates. Estimates are used in the following areas, among others: prepaid and accrued research and development expense, stock-based compensation expense, revenue and income taxes. Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents consist of all cash on hand, deposits and funds invested in available-for-sale securities with original maturities of three months or less at the time of purchase. At September 30, 2018, the Company’s cash is primarily in money market funds. The Company may maintain balances with its banks in excess of federally insured limits. Restricted cash is included in “other assets” in the unaudited condensed consolidated balance sheets. The following provides a reconciliation of cash, cash equivalents, and restricted cash reported in the consolidated balance sheet that sum to the total of the amounts reported in the unaudited condensed consolidated statement of cash flows (in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 162,430 $ 89,599 Other assets 1,566 1,281 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 163,996 $ 90,880 Restricted cash represents amounts required for security deposits under our office and lab space lease agreement. Investments Management determines the appropriate classification of securities at the time of purchase and reevaluates such designation as of each balance sheet date of Revenue Recognition To date, the Company has not generated any revenue from the sales of products. Unless and until the Merger is completed, for the foreseeable future, the Company expects substantially all of its revenues will be generated from its collaborations with MTPC and Otsuka, see Note 3, and any other collaborations the Company may enter into. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for collaborations and other revenues, see Note 3 below. Collaboration Revenues The Company enters into out-license and collaboration agreements which are within the scope of ASC 606, under which it licenses certain rights to its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; development, regulatory, and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. Each of these payments may result in license, collaboration and other revenue, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenues. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company implements the five-step model noted above. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine whether the individual deliverables represent separate performance obligations or whether they must be accounted for as a combined performance obligation as well as the stand-alone selling price for each performance obligation identified in the contract. A deliverable represents a separate performance obligation if both of the following criteria are met: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer, and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. With regard to the MTPC and Otsuka collaboration agreements, the Company recognizes revenue related to amounts allocated to the identified performance obligation on a proportional performance basis as the underlying services are performed. Licenses of Intellectual Property If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company will evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to assess the milestone as probable of being achieved. There is considerable judgment involved in determining whether a milestone is probable of being reached at each specific reporting period. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the customer, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenues as, or when, the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company will re-evaluate the probability of achievement of such development milestones and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenue in the period of adjustment. Manufacturing Supply Services Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. If the Company is entitled to additional payments when the licensee exercises these options, any additional payments are recorded in license, collaboration and other revenues when the licensee obtains control of the goods, which is upon delivery. Royalties The Company will recognize sales-based royalties, including milestone payments based on the level of sales, at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date the Company has not recognized any royalty revenue resulting from its collaboration agreements. Collaborative Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC Topic 808, Collaborative Arrangements Revenue from Contracts with Customers – Scope and Scope Exceptions During the three months ended September 30, 2018, the Company incurred approximately $0.2 million of costs related to the cost-sharing provisions of the Otsuka U.S. Agreement, as defined below in Note 3, of which approximately $0.1 million are reimbursable by Otsuka and recorded as a reduction to research and development expense during the three months ended September 30, 2018. 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 5. The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The rate implicit within the Company’s capital lease obligation approximates market interest rates. Net Loss per Share Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the diluted net loss per share calculation, stock options, warrants, restricted stock and RSUs are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Diluted net income per share is calculated by dividing the net income by the weighted-average shares outstanding for the period, including any dilutive effect from outstanding options, warrants, restricted stock and RSUs using the treasury stock method. Property and Equipment Property and equipment is stated at cost, less accumulated depreciation. Assets under capital lease are included in property and equipment. Property and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors, operating losses, unused capacity, market value declines and technological obsolescence. Recorded values of asset groups of equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale). The following is the summary of property and equipment and related accumulated depreciation as of September 30, 2018 and December 31, 2017. Useful Life September 30, 2018 December 31, 2017 (in thousands) Computer equipment and software 3 $ 914 $ 630 Furniture and fixtures 5 845 800 Equipment 7 1,011 628 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 2,621 2,582 Office equipment under capital lease 3 114 36 5,505 4,676 Less accumulated depreciation (1,697 ) (1,059 ) Net property and equipment $ 3,808 $ 3,617 Depreciation expense, including expense associated with assets under capital leases, was approximately $0.2 million for each of the three months ended September 30, 2018 and 2017, and approximately $0.6 million and $0.4 million for the nine months ended September 30, 2018 and 2017, respectively.

Strategic Collaborations and Ot

Strategic Collaborations and Other Significant Agreements	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Strategic Collaborations and Other Significant Agreements	3. Strategic Collaborations and Other Significant Agreements The Company recognized $53.2 million and $41.3 million in collaboration revenue for the three months ended September 30, 2018 and 2017, respectively, and approximately $147.9 million and $90.7 million for the nine months ended September 30, 2018 and 2017, respectively. The $53.2 million in collaboration revenue for the three months ended September 30, 2018 included $53.1 million of the transaction price for the Company’s collaboration agreements with Otsuka (discussed below), all of which are recognized based on a proportional performance method, and approximately $25,000 for other services related to clinical and regulatory related activities performed by the Company on behalf of MTPC that are not included in the performance obligations identified under the MTPC Agreement. The $147.9 million in collaboration revenue for the nine months ended September 30, 2018 included $147.5 million of the transaction price for the MTPC Agreement and the Company’s collaboration agreements with Otsuka and $0.3 million for other services related to clinical and regulatory related activities performed by the Company on behalf of MTPC that are not included in the performance obligations identified under the MTPC Agreement. During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following revenues from its strategic collaboration agreements and had the following deferred revenue balances as of September 30, 2018: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Collaboration Revenue: (in thousands) (in thousands) MTPC Agreement $ — $ — $ 9,281 $ — Otsuka U.S. Agreement 29,030 22,519 75,086 60,001 Otsuka International Agreement 24,114 18,764 63,176 30,667 Total Proportional Performance Revenue $ 53,144 $ 41,283 $ 147,543 $ 90,668 MTPC Stability Studies 25 — 349 — Total Collaboration Revenue $ 53,169 $ 41,283 $ 147,892 $ 90,668 September 30, 2018 Short-Term Long-Term Total Deferred Revenue: (in thousands) MTPC Agreement $ — $ — $ — Otsuka U.S. Agreement 41,152 43,669 84,821 Otsuka International Agreement 28,947 33,076 62,023 Vifor Agreement — 4,679 4,679 Total $ 70,099 $ 81,424 $ 151,523 The following table presents changes in the Company’s contract assets and liabilities during the nine months ended September 30, 2018 and 2017 (in thousands): Nine Months Ended September 30, 2018 Balance at Beginning of Period Additions Deductions Balance at End of Period Contract assets: Other current assets $ — $ 531 $ (531 ) $ — Accounts receivable (1) $ 34,186 $ 120,283 $ (153,938 ) $ 531 Contract liabilities Deferred revenue $ 179,624 $ 119,442 $ (147,543 ) $ 151,523 Accounts payable $ — $ 4,427 $ (1,040 ) $ 3,387 Nine Months Ended September 30, 2017 Contract assets - Accounts receivable $ 33,823 $ 9,138 $ (42,961 ) $ — Contract liabilities - Deferred revenue $ 197,289 $ 99,111 $ (90,668 ) $ 205,732 (1) During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods (in thousands): Three Months Ended September 30, Nine Months Ended September 30, Revenue Recognized in the Period from: 2018 2017 2018 2017 Amounts included in deferred revenue at the beginning of the period $ 53,144 $ 41,026 $ 110,974 $ 60,001 Performance obligations satisfied in previous periods $ — $ — $ 6,813 $ — Mitsubishi Tanabe Pharma Corporation Collaboration Agreement Summary of Agreement On December 11, 2015, the Company and MTPC entered into a collaboration agreement, or the MTPC Agreement, providing MTPC with exclusive development and commercialization rights to vadadustat in Japan and certain other Asian countries, collectively, the MTPC Territory. In addition, the Company will supply vadadustat for both clinical and commercial use in the MTPC Territory, subject to MTPC’s option to manufacture commercial drug product in the MTPC Territory. The Company and MTPC agreed that, instead of including Japanese patients in the Company’s global Phase 3 program for vadadustat, MTPC would be the sponsor of a Phase 3 program for vadadustat in Japan. Following consultation with the Japanese Pharmaceuticals and Medical Devices Agency, or the PMDA, MTPC initiated its Phase 3 development program for vadadustat in Japan in the fourth quarter of 2017. MTPC is responsible for the costs of the Phase 3 program in Japan and other studies required there, and will make no funding payments for the global Phase 3 program. In consideration for the exclusive license and other rights contained in the MTPC Agreement, MTPC is obligated to make payments totaling up to $265.0 million, comprised of a $20.0 million upfront payment, up to $50.0 million in specified development and regulatory milestones, up to $175.0 million in specified commercial milestones, and a $20.0 million advance payment for Phase 2 studies in Japanese patients completed by the Company and reimbursable by MTPC, as well as tiered double-digit royalty payments of up to 20% on sales of vadadustat in the MTPC Territory. The Company completed its Phase 2 study of vadadustat in non-dialysis dependent, or NDD, Japanese patients in Japan and reported top-line data in the third quarter of 2017. The Company also announced top-line data on its Phase 2 study of vadadustat in dialysis dependent, or DD, Japanese patients in Japan in the first quarter of 2018. The costs of these Phase 2 studies are reimbursable by MTPC. MTPC is obligated to reimburse the Company for costs to complete the Phase 2 studies in excess of the $20.0 million advance payment. The Company incurred approximately $20.5 million in Phase 2 costs through June 30, 2018 and did not incur any additional costs subsequent to June 30, 2018 as the studies have been completed. As a result, MTPC is required to reimburse the Company an additional approximately $0.5 million related to the two Phase 2 studies. MTPC has sole responsibility for the commercialization of vadadustat in the MTPC Territory as well as for Medical Affairs (as defined in the MTPC Agreement) in the MTPC Territory. Akebia is responsible for manufacturing and supplying vadadustat for clinical use in the MTPC Territory. Akebia will enter into a supply agreement with MTPC for the commercial supply of vadadustat prior to commercial launch. The Company and MTPC have established a joint steering committee pursuant to the MTPC Agreement to oversee development and commercialization of vadadustat in the MTPC Territory, including approval of any development or commercialization plans. Unless earlier terminated, the MTPC Agreement will continue in effect on a country-by-country basis until the later of the following: expiration of the last-to-expire patent covering vadadustat in such country in the MTPC Territory; expiration of marketing or regulatory exclusivity in such country in the MTPC Territory; or ten years after the first commercial sale of vadadustat in such country in the MTPC Territory. MTPC may terminate the MTPC Agreement upon twelve months’ notice at any time after the second anniversary of the effective date of the MTPC Agreement. Either party may terminate the MTPC Agreement upon the material breach of the other party that is not cured within a specified time period or upon the insolvency of the other party. MTPC is required to make certain milestone payments to the Company aggregating to approximately $225.0 million upon the achievement of specified development, regulatory and commercial events. More specifically, the Company received $10.0 million in development milestone payments and is eligible to receive up to $40.0 million in regulatory milestone payments for the first product to achieve the associated event, and up to $175.0 million in commercial milestone payments associated with aggregate sales of all products. Additionally, if vadadustat is commercialized, the Company would be entitled to receive tiered royalty payments in the low double digits based on a percentage of net sales. Royalty payments are subject to certain reductions, including upon the introduction of competitive products in certain instances. Royalties are due on a country-by-country basis from the date of first commercial sale of a licensed product in a country until the last to occur of: (i) the expiration of the last to expire valid claim within the intellectual property covering the licensed product, (ii) the expiration of marketing or regulatory exclusivity in such country, or (iii) the tenth anniversary of the first commercial sale of such licensed product in such country. Due to the uncertainty of pharmaceutical development and the high historical failure rates associated with drug development, although the Company has received $10.0 million in development milestones, no additional milestone or royalty payments may ever be received from MTPC. In September 2017, the Company provided MTPC with an option to access data from the Company’s global Phase 3 vadadustat program for payments to the Company of up to $25.0 million. Revenue Recognition The Company evaluated the elements of the MTPC Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, MTPC, is a customer. The Company’s arrangement with MTPC contains the following material promises under the contract at inception: (i) license under certain of the Company’s intellectual property to develop and commercialize vadadustat (the License Deliverable) in the MTPC Territory, (ii) clinical supply of vadadustat (the Clinical Supply Deliverable), (iii) knowledge transfer, (iv) Phase 2 dosing study research services (the Research Deliverable), and (v) rights to future know-how. The Company has identified two performance obligations in connection with its material promises under the MTPC Agreement. Factors considered in making the assessment of which material promises will be accounted for as separate performance obligations included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the good or service is highly interdependent or highly interrelated to the other elements in the arrangement, and whether there are other vendors that can provide the items. Additionally, the MTPC Agreement does not include a general right of return. The two performance obligations identified in connection with the Company’s obligations under the MTPC Agreement are as follows: (i) License, Research and Clinical Supply Performance Obligation The License Deliverable does not have standalone functionality from the Clinical Supply Deliverable. More specifically, the license delivered to MTPC does not provide the right to manufacture vadadustat. MTPC therefore, is prohibited from manufacturing any licensed product during clinical trials. Accordingly, MTPC must obtain the clinical trial products from the Company, which significantly limits the ability for MTPC to use the license for their intended use in a way that generates economic benefits . The License Deliverable does not have standalone functionality from the knowledge transfer because MTPC cannot fully utilize the license for its intended purpose without the corresponding information regarding know-how, development data and regulatory materials possessed by the Company. The License Deliverable does not have standalone functionality from the Research Deliverable because MTPC cannot fully utilize the license for its intended purpose without the performance of the Phase 2 dosing studies. The Phase 2 dosing studies needed to be performed prior to the PMDA approving any Phase 3 study to be performed in the MTPC Territory. Furthermore, MTPC cannot benefit from the Phase 2 dosing studies without the license and the undelivered Phase 3 clinical supply. The License Deliverable does not have standalone functionality from the clinical supply, knowledge transfer or Phase 2 studies. As a result, the License Deliverable, clinical supply, knowledge transfer and Phase 2 studies do not qualify for separation and have been combined as a single performance obligation (the License, Research and Clinical Supply Performance Obligation). (ii) Rights to Future Know-How Performance Obligation The License, Research and Clinical Supply Deliverables combined have standalone functionality from the rights to future know how because MTPC can obtain the value of the License, Research and Clinical Supply Deliverables without receipt of any rights to future know how that may be discovered or developed in the future. As a result, the rights to future know how qualify for separation from the License, Research and Clinical Supply Performance Obligation. The Company allocates the transaction price to each performance obligation based on the Company’s best estimate of the relative standalone selling price. The Company developed a best estimate of the standalone selling price for the Rights to Future Know How Performance Obligation primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement. The Company did not develop a best estimate of standalone selling price for the License, Research and Clinical Supply Performance Obligation because the estimate of standalone selling price associated with the Rights to Future Know How Performance Obligation was determined to be immaterial. The Company has concluded that a change in the key assumptions used to determine the best estimate of standalone selling price for each performance obligation would not have a significant impact on the allocation of arrangement consideration. The transaction price at inception was comprised of: (i) the up-front payment, (ii) the estimated cost for the Phase 2 studies, (iii) a non-substantive milestone associated with the first patient enrolled in the NDD-CKD Phase 3 study, and (iv) the cost of all clinical supply provided to MTPC for the Phase 3 studies. No other development and no regulatory milestones have been included in the transaction price at inception, as all other milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. The total aggregate amount of development milestones is $10.0 million and the total aggregate amount of the regulatory milestones is up to $40.0 million. The total aggregate amount of sales milestones is up to $175.0 million. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to MTPC and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. No amounts were allocated to the Rights to Know How Performance Obligation because the associated best estimate of standalone selling price was determined to be immaterial therefore the arrangement consideration will be allocated to the License, Research and Clinical Supply Performance Obligation. As of September 30, 2018, the transaction price is comprised of: (i) the up-front payment of $20.0 million, (ii) the cost for the Phase 2 studies of $20.5 million, (iii) the cost of all clinical supply provided to MTPC for the Phase 3 studies, and (iv) $10.0 million in development milestones received, comprised of a $6.0 million and a $4.0 million development milestone. All development milestones have been reached and no regulatory milestones have been assessed as probable of being reached as of September 30, 2018. Revenue for the License, Research and Clinical Supply Performance Obligation for the MTPC Agreement is being recognized using a proportional performance method using the Company’s delivery of clinical supply of vadadustat to MTPC for the Phase 3 study as the basis. The Company recognized no revenue during the three months ended September 30, 2018, with respect to the MTPC Agreement as all deliverables were completed in the second quarter of 2018, and approximately $9.3 million during the nine months ended September 30, 2018. The revenue is classified as collaboration revenue in the accompanying unaudited condensed consolidated statements of operations. No revenues were recognized for the three and nine months ended September 30, 2017 with respect to the MTPC Agreement. As of September 30, 2018, there is no deferred revenue, approximately $0.5 million in accounts receivable, all of which is in unbilled accounts receivable. U.S. Collaboration and License Agreement with Otsuka Pharmaceutical Co. Ltd. Summary of Agreement On December 18, 2016, the Company entered into a collaboration and license agreement with Otsuka, or the Otsuka U.S. Agreement. The collaboration is focused on the development and commercialization of vadadustat in the United States. Under the terms of the Otsuka U.S. Agreement, the Company is responsible for leading the development of vadadustat, including the ongoing Phase 3 development program. The Company and Otsuka will co-commercialize vadadustat in the United States, subject to the approval of vadadustat by the FDA. Under the terms of the Otsuka U.S. Agreement, the Company granted to Otsuka a co-exclusive, non-sublicensable license under certain intellectual property controlled by the Company solely to perform medical affairs activities and to conduct non-promotional and commercialization activities related to vadadustat in accordance with the associated plans. The co-exclusive license relates to activities that will be jointly conducted by the Company and Otsuka pursuant to the terms of the Otsuka U.S. Agreement. Pursuant to the terms of the Otsuka U.S. Agreement, the Company is responsible for performing all activities related to the development of vadadustat as outlined in the current global development plan. The current global development plan encompasses all activities with respect to the ongoing PRO 2 2 Under the Otsuka U.S. Agreement, the parties jointly conduct, and have equal responsibility for, all medical affairs, commercialization and non-promotional activities pursuant to underlying plans as agreed to by the parties. If approved by the FDA, the Company will provide vadadustat to Otsuka for commercialization pursuant to a separate supply agreement to be negotiated. The activities under the Otsuka U.S. Agreement are governed by a joint steering committee, or JSC, formed by an equal number of representatives from the Company and Otsuka. The JSC coordinates and monitors the parties’ activities under the collaboration. Among other responsibilities, the JSC manages the overall strategic alignment between the parties, oversees the current global development plan and reviews other detailed plans setting forth the parties’ activities under the arrangement, including the medical affairs plan and commercialization and non-promotional activities plan. Additionally, the parties established a joint development committee, or JDC, which is comprised of an equal number of representatives from the Company and Otsuka. Among other responsibilities, the JDC shares information related to, and reviews and discusses activities and progress under, the current global development plan and any other development that may be conducted pursuant to the collaboration. The Company and Otsuka also established a joint manufacturing committee, or JMC, which is comprised of an equal number of representatives from each of the parties. Among other responsibilities, the JMC oversees the manufacturing plan and related manufacturing activities. In support of the potential commercialization of vadadustat, the parties established a joint commercialization committee, or JCC, which is comprised of an equal number of representatives from the Company and Otsuka. Among other responsibilities, the JCC oversees the activities and progress under the commercialization and non-promotional activities plan and all other sales and marketing activities. Subject to the terms of the Otsuka Funding Option, as described below, the Company has retained final decision‑making authority with respect to all development matters, U.S. pricing strategy and certain other key commercialization matters. Under the terms of the Otsuka U.S. Agreement, the Company received a $125.0 million up-front, non-refundable, non-creditable cash payment in December 2016. In March 2017, the Company received a payment of approximately $33.8 million, which represents reimbursement for Otsuka’s share of costs previously incurred by the Company in implementing the current global development plan through December 31, 2016. Commencing in the third quarter of 2017, whereupon the Company had incurred a specified amount of incremental costs, Otsuka began to contribute, as required by the Otsuka U.S. Agreement, a percentage of the remaining costs incurred under the current global development plan. The Company estimates that Otsuka’s funding of the current global development plan costs subsequent to December 31, 2016 will total $167.5 million or more, depending on the actual costs incurred toward the current global development plan. The costs associated with the performance of any development activities in addition to those outlined in the current global development plan will be subject to a cost sharing or reimbursement mechanism to be determined by the parties. Costs incurred with respect to medical affairs and commercialization and non-promotional activities will generally be shared equally by the parties. In addition, if the costs incurred in completing the activities under the current global development plan exceed a certain threshold, or the Cost Threshold, then the Company may elect to require Otsuka to increase the aggregate percentage of current global development costs it funds under the Otsuka U.S. Agreement and the Otsuka International Agreement, as defined below, from 52.5% to 80%, or the Otsuka Funding Option. In such event, the excess of the payments made under such election and Otsuka’s allocated share of the current global development costs is fully creditable against future payments due to the Company under the arrangement, provided that future payments due to the Company may not be reduced by more than 50% in any calendar year and any remaining creditable amount above 50% in any calendar year will be applied to subsequent future payments until fully credited. In addition, decisions regarding certain development matters will be made jointly by the Company and Otsuka in accordance with the procedures set forth in the Otsuka U.S. Agreement. In September 2018, the Company exercised the Otsuka Funding Option, which will be effective when the Cost Threshold is exceeded. The Company estimates that the Cost Threshold will be exceeded in the second quarter of 2019. In addition, Otsuka would be required to make certain milestone payments to the Company upon the achievement of specified development, regulatory and commercial events. More specifically, the Company is eligible to receive up to $125.0 million in development milestone payments and up to $65.0 million in regulatory milestone payments for the first licensed product to achieve the associated event. Moreover, the Company is eligible for up to $575.0 million in commercial milestone payments associated with aggregate sales of licensed products. Due to the uncertainty of pharmaceutical development and the high historical failure rates associated therewith, no milestone payments may ever be received from Otsuka. Under the Otsuka U.S. Agreement, the Company and Otsuka share the costs of developing and commercializing vadadustat in the United States and the profits from the sales of vadadustat after approval by the FDA. In connection with the profit share calculation, net sales include gross sales to third-party customers net of discounts, rebates, chargebacks, taxes, freight and insurance charges and other applicable deductions. Shared costs generally include costs attributable or reasonably allocable to the manufacture of vadadustat for commercialization purposes and the performance of medical affairs activities, non-promotional activities and commercialization activities. Unless earlier terminated, the Otsuka U.S. Agreement will expire in the U.S. on a product-by-product basis on the date that one or more generic versions of vadadustat first achieves 90% market penetration. Either party may terminate the Otsuka U.S. Agreement in its entirety upon an uncured breach or insolvency on the part of the other party. Otsuka may terminate the Otsuka U.S. Agreement in its entirety upon 12 months’ prior written notice at any time after the release of the first topline data from the global Phase 3 development program for vadadustat. In the event of termination of the Otsuka U.S. Agreement, all rights and licensees granted to Otsuka under the Otsuka U.S. Agreement will automatically terminate and the licenses granted to the Company will become freely sublicensable. In addition, the upfront payment, all development costs and milestone payments received by the Company prior to such termination will not be refunded to Otsuka. Revenue Recognition The Company evaluated the elements of the Otsuka U.S. Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, Otsuka, is a customer. The Company’s arrangement with Otsuka contains the following material promises under the contract at inception: (i) license under certain of the Company’s intellectual property to develop, perform medical affairs activities with respect to and conduct non-promotional and commercialization activities related to vadadustat and products containing or comprising vadadustat (the License Deliverable), (ii) development services to be performed pursuant to the current global development plan (the Development Services Deliverable), (iii) rights to future intellectual property (the Future IP Deliverable), and (iv) joint committee services (the Committee Deliverable). The Company has identified three performance obligations in connection with its obligations under the Otsuka U.S. Agreement. Factors considered in making the assessment of which material promises will be accounted for as separate performance obligations included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the good or service is highly interdependent or highly interrelated to the other elements in the arrangement, and whether there are other vendors that can provide the items. Additionally, the Otsuka U.S. Agreement does not include a general right of return. The three performance obligations identified in connection with the Company’s obligations under the Otsuka U.S. Agreement are as follows: (i) License and Development Services Combined (License Performance Obligation) The License Deliverable does not have standalone functionality from the Development Services Deliverable, due to the limitations inherent in the license conveyed. More specifically, the license conveyed to Otsuka does not provide Otsuka with the right to manufacture vadadustat and products containing or comprising vadadustat. However, the manufacturing and supply services that are conducted as part of the services to be performed pursuant to the current global development plan are necessary for Otsuka to fully exploit the associated license for its intended purpose. The value of the rights provided through the license conveyed will be realized when the underlying products covered by the intellectual property progress through the development cycle, receive regulatory approval and are commercialized. Products containing or comprising vadadustat cannot be commercialized until the development services under the current global development plan are completed. Accordingly, Otsuka must obtain the manufacturing and supply of the associated products that are included within the development services to be performed pursuant to the current global development plan from the Company in order to derive benefit from the license, which significantly limits the ability for Otsuka to utilize the License Deliverable for its intended purpose in a way that generates economic benefits. (ii) Rights to Future Intellectual Property (Future IP Performance Obligation) The License and Development Services deliverables combined have standalone functionality from the Future IP Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development services without the receipt of any other intellectual property that may be discovered or developed in the future. The Future IP Deliverable also has standalone functionality from the Committee Deliverable because the joint committee services have no bearing on the value to be derived from the rights to potential future intellectual property. As a result, the Future IP Deliverable qualifies as a separate performance obligation. (iii) Joint Committee Services (Committee Performance Obligation) The License and Development Services deliverables combined have standalone functionality from the Committee Deliverable because Otsuka can obtain the value of the license using the clinical trial materials implicit in the development services without the joint committee services. The Committee Deliverable also has standalone functionality from the rights to Future IP Deliverable because the joint committee services have no bearing on the value to be derived from the rights to potential future intellectual property. As a result, the Committee Deliverable qualifies as a separate performance obligation. The Company allocates the transaction price to each performance obligation based on the Company’s best estimate of the relative standalone selling price. The Company developed a best estimate of standalone selling price for the Committee Performance Obligation after considering the nature of the services to be performed and estimates of the associated effort and rates applicable to such services that would be expected to be realized under similar contracts. The Company developed a best estimate of standalone selling price for the Future IP Performance Obligation primarily based on the likelihood that additional intellectual property covered by the license conveyed will be developed during the term of the arrangement. The Company did not develop a best estimate of standalone selling price for the License Performance Obligation due to the following: (i) the best estimates of standalone selling price associated with the Future IP Performance Obligation was determined to be immaterial and (ii) the period of performance and pattern of recognition for the License Performance Obligation and the Committee Performance Obligation was determined to be similar. The Company has concluded that a change in the key assumptions used to determine the best estimate of standalone selling price for each performance obligation would not have a significant impact on the allocation of arrangement consideration. The transaction price at inception was comprised of: (i) the up-front payment, (ii) the cost share payment with respect to amounts incurred by the Company through December 31, 2016, and (iii) an estimate of the cost share payments to be received with respect to amounts incurred by the Company subsequent to December 31, 2016. No development or regulatory milestones were included in the transaction price at inception, as all milestone amounts were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. No amounts were allocated to the Future IP Performance Obligation because the associated best estimate of standalone selling price was determined to be immaterial. Due to the similar performance period and recognition pattern between the License Performance Obligation and the Committee Performance Obligation, the transaction price has been allocated to the License Performance Obligation and the Committee Performance Obligation on a combined basis. Accordingly, the Company will recognize revenue related to the allocable arran

Available for Sale Securities

Available for Sale Securities	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Available for Sale Securities	4. Available For Sale Securities Available for sale securities at September 30, 2018 and December 31, 2017 consist of the following : Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) September 30, 2018 Cash and cash equivalents $ 162,430 $ — $ — $ 162,430 Available for sale securities: Certificates of deposit $ 445 $ — $ — $ 445 U.S. government debt securities 177,181 — (363 ) 176,818 Corporate debt securities 50,497 — (46 ) 50,451 Total available for sale securities $ 228,123 $ — $ (409 ) $ 227,714 Total cash, cash equivalents, and available for sale securities $ 390,553 $ — $ (409 ) $ 390,144 Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) December 31, 2017 Cash and cash equivalents $ 70,156 $ — $ — $ 70,156 Available for sale securities: Certificates of deposit $ 14,117 $ — $ — $ 14,117 U.S. government debt securities 175,155 — (352 ) 174,803 Corporate debt securities 58,806 — (90 ) 58,716 Total available for sale securities $ 248,078 $ — $ (442 ) $ 247,636 Total cash, cash equivalents, and available for sale securities $ 318,234 $ — $ (442 ) $ 317,792 The estimated fair value of the Company’s available for sale securities balance at September 30, 2018, by contractual maturity, is as follows: Due in one year or less $ 212,725 Due after one year 14,989 Total available for sale securities $ 227,714 There were no realized gains or losses on available for sale securities for the nine months ended September 30, 2018 and 2017. The following table summarizes the Company’s available for sale securities that were in a continuous unrealized loss position, but were not deemed to be other-than temporarily impaired, as of September 30, 2018 and December 31, 2017: Unrealized Loss for Less Than 12 Months Unrealized Loss for 12 Months or More Total Gross Gross Gross Unrealized Estimated Unrealized Estimated Unrealized Estimated Losses Fair Value Losses Fair Value Losses Fair Value (in thousands) September 30, 2018 Available for sale securities: U.S. government debt securities $ (342 ) $ 158,845 $ (21 ) $ 14,981 $ (363 ) $ 173,826 Corporate debt securities (38 ) 42,009 (8 ) 7,470 (46 ) 49,479 Total $ (380 ) $ 200,854 $ (29 ) $ 22,451 $ (409 ) $ 223,305 Unrealized Loss for Less Than 12 Months Unrealized Loss for 12 Months or More Total Gross Gross Gross Unrealized Estimated Unrealized Estimated Unrealized Estimated Losses Fair Value Losses Fair Value Losses Fair Value (in thousands) December 31, 2017 Available for sale securities: U.S. government debt securities $ (343 ) $ 170,812 $ (9 ) $ 3,991 $ (352 ) $ 174,803 Corporate debt securities (90 ) 58,716 — — (90 ) 58,716 Total $ (433 ) $ 229,528 $ (9 ) $ 3,991 $ (442 ) $ 233,519 There were 49 securities and 60 securities as of September 30, 2018 and December 31, 2017, respectively, that were in an unrealized loss position. The Company considered the decline in the market value of these securities to be primarily attributable to current economic conditions. The contractual terms of these securities do not permit the issuer to settle the securities at a price less than the amortized cost basis of the investment. As of September 30, 2018, the Company does not intend to sell these securities and it was not more likely than not that the Company would be required to sell these securities before the recovery of their amortized cost basis, which may be at maturity. As a result, the Company did not consider these investments to be other-than-temporarily impaired as of September 30, 2018.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	5. Fair Value of Financial Instruments The Company utilizes a portfolio management company for the valuation of the majority of its investments. This company is an independent, third-party vendor recognized to be an industry leader with access to market information that obtains or computes fair market values from quoted market prices, pricing for similar securities, recently executed transactions, cash flow models with yield curves and other pricing models. For valuations obtained from the pricing service, the Company performs due diligence to understand how the valuation was calculated or derived, focusing on the valuation technique used and the nature of the inputs. Based on the fair value hierarchy, the Company classifies its cash equivalents and marketable securities within Level 1 or Level 2. This is because the Company values its cash equivalents and marketable securities using quoted market prices or alternative pricing sources and models utilizing market observable inputs. Assets measured or disclosed at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 are summarized below: Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) September 30, 2018 Assets: Cash and cash equivalents $ 162,430 $ — $ — $ 162,430 Certificates of deposit — 445 — 445 U.S. government debt securities — 176,818 — 176,818 Corporate debt securities — 50,451 — 50,451 $ 162,430 $ 227,714 $ — $ 390,144 Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) December 31, 2017 Assets: Cash and cash equivalents $ 70,156 $ — $ — $ 70,156 Certificates of deposit — 14,117 — 14,117 U.S. government debt securities — 174,803 — 174,803 Corporate debt securities — 58,716 — 58,716 $ 70,156 $ 247,636 $ — $ 317,792 The Company’s corporate debt securities are all investment grade. The Company had no assets or liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3) at September 30, 2018 and December 31, 2017. 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	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Accrued Expenses	6. Accrued Expenses Accrued expenses as of September 30, 2018 and December 31, 2017 are as follows: September 30, 2018 December 31, 2017 (in thousands) Accrued clinical expenses $ 80,315 $ 43,297 Accrued bonus 3,481 3,388 Merger costs 2,084 — Professional fees 1,537 808 Accrued vacation 858 797 Accrued payroll 398 795 Accrued severance 40 — Income tax payable — 987 Accrued other 5,903 2,369 Total accrued expenses $ 94,616 $ 52,441

Warrant

Warrant	9 Months Ended
	Sep. 30, 2018
Warrant Disclosure [Abstract]
Warrant	7. Warrant In connection with the Janssen Agreement, in February 2017 the Company issued a warrant to purchase 509,611 shares of the Company’s common stock at an exercise price of $9.81 per share. The warrant was fully vested upon issuance and is exercisable in whole or in part, at any time prior to the fifth anniversary of the date of issuance. The warrant satisfied the equity classification criteria of ASC 815, and is therefore classified as an equity instrument. The fair value at issuance of $3.4 million was calculated using the Black Scholes option pricing model and was charged to research and development expense as it represented consideration for a license for which the underlying intellectual property was deemed to have no alternative future use. As of September 30, 2018, the warrant remains outstanding and expires on February 9, 2022.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Authorized and Outstanding Capital Stock As of September 30, 2018, the authorized capital stock of the Company included 175,000,000 shares of common stock, par value $0.00001 per share, of which 57,046,563 and 47,612,619 shares are issued and outstanding at September 30, 2018 and December 31, 2017, 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 September 30, 2018 and December 31, 2017. At-the-Market Facility In May 2016, the Company established an at-the-market, or ATM, equity offering program pursuant to which it was able to offer and sell up to $75.0 million of common stock at the then current market prices from time to time. In September 2016, the Company commenced sales under this program. Through December 31, 2017, the Company sold 1,080,908 shares of common stock under this program with net proceeds (after deducting commissions and other offering expenses) of $12.1 million, of which 150,023 shares were sold in the nine months ended September 30, 2017 for net proceeds (after deducting commissions and other offering expenses) of approximately $1.6 million. Additionally, the Company sold 694,306 shares in the three months ended March 31, 2018 for net proceeds (after deducting commissions and other offering expenses) of approximately $10.5 million. The Company has not sold any additional shares under this program subsequent to March 31, 2018. Equity Offering In March 2018, the Company completed a follow-on public equity offering, whereby the Company sold 8,500,000 shares of common stock at a public offering price of $10.50 per share. The aggregate net proceeds received by the Company from the offering were approximately $84.8 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company. Equity Plans On February 28, 2014, the Company’s Board of Directors adopted its 2014 Incentive Plan, or the 2014 Plan, and its 2014 Employee Stock Purchase Plan, or the ESPP, which were subsequently approved by its stockholders and became effective upon the closing of the Company’s initial public offering on March 25, 2014. The 2014 Plan replaced the 2008 Equity Incentive Plan, as amended, the 2008 Plan; however, options or other awards granted under the 2008 Plan prior to the adoption of the 2014 Plan that have not been settled or forfeited remain outstanding and effective. In May 2016 the Company’s Board of Directors approved an inducement award program that was separate from the Company’s equity plans and which, consistent with Nasdaq Listing Rule 5635(c)(4), did not require shareholder approval, the Inducement Award Program. For 2018, the Company authorized the issuance of up to 750,000 shares for the purpose of granting options to purchase shares of the Company’s common stock to new hires under the Inducement Award Program, of which 255,550 options to purchase shares were granted during the nine months ended September 30, 2018 and 249,550 options to purchase shares remain outstanding as of September 30, 2018. The 2014 Plan allows for the granting of stock options, stock appreciation rights, or SARs, restricted stock, unrestricted stock, RSUs, performance awards and other awards convertible into or otherwise based on shares of our common stock. Dividend equivalents may also be provided in connection with an award under the 2014 Plan. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2014 Plan. The Company initially reserved 1,785,000 shares of its common stock for the issuance of awards under the 2014 Plan. The 2014 Plan provides that the number of shares reserved and available for issuance under the 2014 Plan will automatically increase annually on January 1 st st st The ESPP provides for the issuance of options to purchase shares of the Company’s common stock to participating employees at a discount to their fair market value. The maximum aggregate number of shares of common stock available for purchase pursuant to the exercise of options granted under the ESPP will be the lesser of (a) 262,500 shares, increased on each anniversary of the adoption of the ESPP by one percent (1%) of the total shares of common stock then outstanding, the ESPP Evergreen Provision, and (b) 739,611 shares, which is equal to five percent (5%) of the total shares of common stock outstanding on the date of the adoption of the ESPP on a fully diluted, as converted basis. Under the ESPP, each offering period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering. The per-share purchase price at the end of each offering period is equal to the lesser of eighty-five percent (85%) of the closing price of our common stock at the beginning or end of the offering period. Shares Reserved for Future Issuance The Company has reserved for future issuance the following number of shares of common stock: September 30, 2018 December 31, 2017 Common stock options and RSUs outstanding (1) 4,851,790 4,388,752 Shares available for issuance under the 2014 Plan (2) 3,347,957 1,790,600 Warrant to purchase common stock 509,611 509,611 Shares available for issuance under the ESPP (3) 603,522 652,290 Total 9,312,880 7,341,253 (1) (2) (3) On February 28, 2016, the shares reserved for future issuance under the ESPP increased by 273,404 shares pursuant to the ESPP Evergreen Provision. There were no increases in the shares reserved for future issuance subsequent to this period as the maximum aggregate number of shares available for purchase had reached its cap of 739,611. Stock-Based Compensation Stock Options On February 28, 2018, as part of the Company’s annual grant of equity, the Company issued 522,200 stock options to employees. In addition, the Company issues stock options to directors, new hires and occasionally to other employees not in connection with the annual grant process. Options granted by the Company vest over periods of between 12 and 48 months, subject, in each case, to the individual’s continued service through the applicable vesting date. Options vest either 100% on the first anniversary of the grant date or in installments of (i) 25% at the one year anniversary and (ii) 12 equal quarterly installments beginning on the first day of each calendar quarter after the one year anniversary of the grant date, subject to the individual’s continuous service with the Company. Options generally expire ten years after the date of grant. The Company recorded approximately $1.5 million and $1.6 million of stock-based compensation expense related to stock options during the three months ended September 30, 2018 and 2017, respectively, and approximately $5.1 million and $4.9 million during the nine months ended September 30, 2018 and 2017, respectively. 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 Company records stock-based compensation expense for restricted stock awards based on the grant date fair value for employees and the reporting date and upon vesting fair value for non-employees. The fair value of the award is considered the intrinsic value as of each measurement date. Compensation expense related to the restricted stock awards was being recognized over the associated requisite service period. The Company recorded approximately $0.1 million and $0.2 million of stock-based compensation expense related to restricted stock during the three and nine months ended September 30, 2017, respectively. Restricted shares were fully vested as of December 31, 2017 and there were no additional grants of restricted stock during the nine months ended September 30, 2018, as such, there was no stock-based compensation expense related to restricted stock during the three and nine months ended September 30, 2018. Restricted Stock Units On February 28, 2018, as part of the Company’s annual grant of equity, the Company issued 367,250 RSUs to employees. In addition, the Company occasionally issues RSUs not in connection with the annual grant process to employees. 100% of each RSU grant vests on either the first or the third anniversary of the grant date, subject, in each case, to the individual’s continued service through the applicable vesting date. The expense recognized for these awards is based on the grant date fair value of the Company’s common stock multiplied by the number of units granted and recognized on a straight-line basis over the vesting period. The Company recorded approximately $0.7 million and $0.4 million of stock-based compensation expense related to the RSUs during the three months ended September 30, 2018 and 2017, respectively, and approximately $1.8 million and $1.5 million during the nine months ended September 30, 2018 and 2017, respectively. Employee Stock Purchase Plan The Company issued 48,768 shares during the nine months ended September 30, 2018. The Company recorded approximately $52,000 and $47,000 of stock-based compensation expense related to the ESPP during the three months ended September 30, 2018 and 2017, respectively, and approximately $0.2 million and $0.1 million during the nine months ended September 30, 2018 and 2017, respectively. Stock-Based Compensation Expense Summary The Company has classified its stock-based compensation expense related to share-based awards as follows: Three Months Ended Nine Months Ended September 30, 2018 September 30, 2017 September 30, 2018 September 30, 2017 (in thousands) (in thousands) Research and development $ 647 $ 569 $ 2,090 $ 5,741 (1) General and administrative 1,605 1,584 4,888 4,346 Total $ 2,252 $ 2,153 $ 6,978 $ 10,087 (1) Compensation expense by type of award: Three Months Ended Nine Months Ended September 30, 2018 September 30, 2017 September 30, 2018 September 30, 2017 (in thousands) (in thousands) Stock options $ 1,458 $ 1,606 $ 5,074 $ 4,927 Restricted stock — 93 — 158 Restricted stock units 742 407 1,751 1,458 Employee stock purchase plan 52 47 153 131 Warrant — — — 3,413 Total $ 2,252 $ 2,153 $ 6,978 $ 10,087

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. There were no significant income tax provisions or benefits for the three and nine months ended September 30, 2018 and 2017. 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. As noted in Note 2, effective January 1, 2018, the Company adopted ASC 606, using the full retrospective transition method. Under this method, the Company has revised its consolidated financial statements for the year ended December 31, 2017, and applicable interim periods within those years, as if ASC 606 had been effective for those periods. The adoption of this guidance did not have a significant impact on the Company’s related tax disclosures. For the year ended December 31, 2017, the Company had taxable income primarily due to timing differences. The income was fully offset with available net operating losses, NOLs, for regular federal and state tax purposes. The Company did have a tax liability for Alternative Minimum Tax in 2017 of approximately $0.8 million; however, due to tax reform, the amount is fully refundable through 2021, and thus the net result is that the Company generated an income tax receivable of approximately $0.8 million rather than a tax expense for the year ended December 31, 2017. During the second quarter of 2018, the Company paid the $0.8 million tax liability, as such, the Company’s unaudited condensed consolidated balance sheet included a tax receivable of approximately $0.8 million, which is included in other assets, and no tax payable as of September 30, 2018. The Tax Cuts and Jobs Act, which was signed on December 22, 2017, made significant change in U.S. tax law including a reduction in U.S. corporate tax rate from 35% to 21% for tax years beginning after December 31, 2017. As a result of the enacted law, the Company was required to revalue deferred tax assets and liabilities existing as of December 31, 2017 from the 35% federal rate in effect through the end of 2017, to the new 21% rate. As a result of the change in law, the Company recorded a $43.0 million reduction in the deferred tax asset and corresponding valuation allowance as of December 31, 2017. In accordance with SAB 118, the Company has determined that its deferred tax asset value and associated valuation allowance reduction is a provisional amount and a reasonable estimate at December 31, 2017. The final impact may differ from this provisional amount due to, among other things, changes in interpretations and assumptions we have made thus far and the issuance of additional regulatory or other guidance. During the nine months ended September 30, 2018, we did not identify any additional adjustments necessary to the deferred tax asset value and associated valuation allowance recorded at December 31, 2017. We expect to complete the final impact within the measurement period.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Leases The Company leases approximately 65,167 square feet of office and lab space in Cambridge, Massachusetts under a lease which was most recently amended in April 2018, collectively the Lease. Under the Third Amendment to Lease, or the Third Amendment, executed in July 2016, total monthly lease payments under the initial base rent were approximately $242,000 and are subject to annual rent escalations. In addition to such annual rent escalations, base rent payments for a portion of said premises commenced on January 1, 2017 in the monthly amount of approximately $22,000. The Fourth Amendment to Lease, executed in May 2017, provided additional storage space to the Company and did not impact rent payments. In April 2018, the Company entered into a Fifth Amendment to Lease, or the Fifth Amendment, for an additional 19,805 square feet of office space on the 12 th Committed landlord contributions included in the Lease totaled $3,289,170, including $1,142,010 in leasehold improvements not yet utilized. The landlord contributions are being accounted for as a deferred lease incentive and reduction in monthly rent expense over the term of the Lease. The term of the Lease with respect to the office space expires on September 11, 2026, with one five year extension option available. The term of the Lease with respect to the lab space expires on November 30, 2021, with an extension option for one additional period of two years. Under the Fifth Amendment, the total security deposit in connection with the Lease increased by $0.5 million from $1.3 million to $1.8 million. In May 2018, the security deposit was reduced by $0.2 million to $1.6 million, which remains in effect as of September 30, 2018 and is in the form of a letter of credit, all of which is included in other current assets in the Company’s condensed consolidated balance sheets as of September 30, 2018. The Company recognizes rent expense for the space it currently occupies under the Lease 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 September 30, 2018 and December 31, 2017. At September 30, 2018, the Company’s future minimum payments required under this Lease are as follows: Operating Lease (in thousands) 2018 $ 896 2019 5,122 2020 5,325 2021 5,355 2022 4,997 Thereafter 18,991 Total $ 40,686 The Company recorded approximately $0.8 million in rent expense for each of the three months ended September 30, 2018 and 2017, respectively, and approximately $2.4 million for each of the nine months ended September 30, 2018 and 2017, respectively. Other Third Party Contracts Under the Company’s agreement with IQVIA, formerly known as Quintiles IMS, to provide contract research organization services for the PRO 2 2

Employee Retirement Plan

Employee Retirement Plan	9 Months Ended
	Sep. 30, 2018
Compensation And Retirement Disclosure [Abstract]
Employee Retirement Plan	11. Employee Retirement Plan During 2008, the Company established a retirement plan, or the 401(k) Plan, authorized by Section 401(k) of the Internal Revenue Code. In accordance with the 401(k) Plan, all employees who have attained the age of 21 are eligible to participate in the 401(k) Plan as of the first Entry Date, as defined therein, 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 $41,000 and $27,000 were made during the three months ended September 30, 2018 and 2017, respectively, and approximately $0.3 million and $0.2 million during the nine months ended September 30, 2018 and 2017, respectively.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Net Loss per Share	12. Net Loss per Share The shares in the table below were excluded from the calculation of diluted net loss per share, prior to the use of the treasury stock method, due to their anti-dilutive effect: As of September 30, 2018 2017 Warrant 509,611 509,611 Outstanding stock options 3,957,940 3,743,303 Unvested restricted stock — 13,982 Unvested restricted stock units 893,850 728,438 Total 5,361,401 4,995,334

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America, or U.S. GAAP, for interim financial reporting and as required by Regulation S-X, Rule 10-01. Accordingly, they do not include all of the information and footnotes required by U.S. GAAP for complete financial statements. 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, or ASC, and Accounting Standards Update, or ASU, of the Financial Accounting Standards Board, or FASB. In the opinion of management, all adjustments, consisting of normal recurring accruals and revisions of estimates, considered necessary for a fair presentation of the unaudited condensed consolidated financial statements have been included. Certain amounts in the prior period financial statements have been revised to conform to the presentation of the current period financial statements. See “New Accounting Pronouncements – Recently Adopted” below for a discussion of certain revisions to prior period financial statements made in connection with the Company’s adoption of new revenue recognition guidance retroactive to January 1, 2016. Otherwise, these reclassifications had no significant effects on the previously reported net loss. Interim results for the three and nine months ended September 30, 2018 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2018 or any other future period. The accompanying unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, Akebia Therapeutics Securities Corporation, Akebia Europe Limited and the Merger Sub. All intercompany balances and transactions have been eliminated in consolidation. Management has determined that the Company operates in one segment, which is the business of developing and commercializing proprietary therapeutics based on HIF biology. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s consolidated financial statements and the accompanying notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the Securities and Exchange Commission on March 12, 2018, or the 2017 Annual Report on Form 10-K. The significant accounting policies used in preparation of these unaudited condensed consolidated financial statements for the three and nine months ended September 30, 2018 are consistent with those discussed in Note 2 to the consolidated financial statements in the Company’s 2017 Annual Report on Form 10-K and are updated below as necessary.
New Accounting Pronouncements	New Accounting Pronouncements – Recently Adopted In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition • For all reporting periods presented before January 1, 2018, the Company has not disclosed the amount of the transaction price allocated to the remaining performance obligations or an explanation of when the Company expects to recognize the amount as revenue. • The Company has not adjusted the promised amount of consideration for the effects of a significant financing component when the Company expects, at contract inception, that the period between when the entity transfers a promised good or a service to a customer and when the customer pays for that good or service will be one year or less. • The Company recognizes the incremental costs of obtaining a contract as an expense when incurred if the amortization period of the asset that the Company otherwise would have recognized is one year or less. The Company, as a result of adopting ASC 606 on January 1, 2018, has revised its comparative financial statements for the prior year as if ASC 606 had been effective for that period, as set forth below. No changes for the adoption of ASC 606 were deemed necessary for the year ended December 31, 2016 and applicable interim periods within the year. With respect to the collaboration agreements with Otsuka Pharmaceutical Co. Ltd., or Otsuka, and Mitsubishi Tanabe Pharma Corporation, or MTPC, the Company concluded that there was no impact to revenue for the three and nine months ended September 30, 2017 after the adoption of ASC 606. As a result, there is no change to the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2017. The changes shown in the table below relate to the Company’s collaboration agreement with MTPC and the impact of when milestone payments can be recognized under the new standard as well as the period over which this revenue is recognized. Under ASC 605-28, Revenue Recognition-Milestone Method December 31, 2017 (in thousands) As revised under ASC 606 As originally reported under ASC 605 Effect of change Short-term deferred revenue $ 81,667 $ 84,910 $ (3,243 ) Accumulated deficit $ (370,807 ) $ (374,050 ) $ 3,243 In October 2016, the FASB issued ASU 2016-18, Restricted Cash , which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally describes as restricted cash or restricted cash equivalents. Therefore, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, and interim periods within those years, using a retrospective transition method to each period presented, with early adoption permitted. The ASU requires the application of a retrospective transition method to each period presented. The Company elected to adopt this ASU effective January 1, 2018. The adoption of this guidance resulted in the relocation of $1.3 million in restricted cash from cash used in operating activities to cash, cash equivalents, and restricted cash at the beginning of the period in the unaudited condensed consolidated statement of cash flows for each of the nine months ended September 30, 2018 and 2017. New Accounting Pronouncements – Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases
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, revenue and income taxes.
Cash, Cash Equivalents, and Restricted Cash	Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents consist of all cash on hand, deposits and funds invested in available-for-sale securities with original maturities of three months or less at the time of purchase. At September 30, 2018, the Company’s cash is primarily in money market funds. The Company may maintain balances with its banks in excess of federally insured limits. Restricted cash is included in “other assets” in the unaudited condensed consolidated balance sheets. The following provides a reconciliation of cash, cash equivalents, and restricted cash reported in the consolidated balance sheet that sum to the total of the amounts reported in the unaudited condensed consolidated statement of cash flows (in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 162,430 $ 89,599 Other assets 1,566 1,281 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 163,996 $ 90,880 Restricted cash represents amounts required for security deposits under our office and lab space lease agreement.
Investments	Investments Management determines the appropriate classification of securities at the time of purchase and reevaluates such designation as of each balance sheet date of
Revenue Recognition	Revenue Recognition To date, the Company has not generated any revenue from the sales of products. Unless and until the Merger is completed, for the foreseeable future, the Company expects substantially all of its revenues will be generated from its collaborations with MTPC and Otsuka, see Note 3, and any other collaborations the Company may enter into. ASC 606 applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for collaborations and other revenues, see Note 3 below. Collaboration Revenues The Company enters into out-license and collaboration agreements which are within the scope of ASC 606, under which it licenses certain rights to its product candidates to third parties. The terms of these arrangements typically include payment to the Company of one or more of the following: non-refundable, up-front license fees; development, regulatory, and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. Each of these payments may result in license, collaboration and other revenue, except for revenues from royalties on net sales of licensed products, which are classified as royalty revenues. In determining the appropriate amount of revenue to be recognized as the Company fulfills its obligations under each of its agreements, the Company implements the five-step model noted above. As part of the accounting for these arrangements, the Company must develop assumptions that require judgment to determine whether the individual deliverables represent separate performance obligations or whether they must be accounted for as a combined performance obligation as well as the stand-alone selling price for each performance obligation identified in the contract. A deliverable represents a separate performance obligation if both of the following criteria are met: (i) the customer can benefit from the good or service either on its own or together with other resources that are readily available to the customer, and (ii) the entity’s promise to transfer the good or service to the customer is separately identifiable from other promises in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include forecasted revenues, development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. With regard to the MTPC and Otsuka collaboration agreements, the Company recognizes revenue related to amounts allocated to the identified performance obligation on a proportional performance basis as the underlying services are performed. Licenses of Intellectual Property If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company will evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes development milestone payments, the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to assess the milestone as probable of being achieved. There is considerable judgment involved in determining whether a milestone is probable of being reached at each specific reporting period. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the customer, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenues as, or when, the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company will re-evaluate the probability of achievement of such development milestones and any related constraint, and if necessary, adjust its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration revenue in the period of adjustment. Manufacturing Supply Services Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. If the Company is entitled to additional payments when the licensee exercises these options, any additional payments are recorded in license, collaboration and other revenues when the licensee obtains control of the goods, which is upon delivery. Royalties The Company will recognize sales-based royalties, including milestone payments based on the level of sales, at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date the Company has not recognized any royalty revenue resulting from its collaboration agreements. Collaborative Arrangements The Company records the elements of its collaboration agreements that represent joint operating activities in accordance with ASC Topic 808, Collaborative Arrangements Revenue from Contracts with Customers – Scope and Scope Exceptions During the three months ended September 30, 2018, the Company incurred approximately $0.2 million of costs related to the cost-sharing provisions of the Otsuka U.S. Agreement, as defined below in Note 3, of which approximately $0.1 million are reimbursable by Otsuka and recorded as a reduction to research and development expense during the three months ended September 30, 2018.
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 5. The carrying amounts of prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to their short-term maturities. The rate implicit within the Company’s capital lease obligation approximates market interest rates.
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the diluted net loss per share calculation, stock options, warrants, restricted stock and RSUs are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Diluted net income per share is calculated by dividing the net income by the weighted-average shares outstanding for the period, including any dilutive effect from outstanding options, warrants, restricted stock and RSUs using the treasury stock method.
Property and Equipment	Property and Equipment Property and equipment is stated at cost, less accumulated depreciation. Assets under capital lease are included in property and equipment. Property and equipment is depreciated using the straight-line method over the estimated useful lives of the assets, generally three to seven years. Such costs are periodically reviewed for recoverability when impairment indicators are present. Such indicators include, among other factors, operating losses, unused capacity, market value declines and technological obsolescence. Recorded values of asset groups of equipment that are not expected to be recovered through undiscounted future net cash flows are written down to current fair value, which generally is determined from estimated discounted future net cash flows (assets held for use) or net realizable value (assets held for sale). The following is the summary of property and equipment and related accumulated depreciation as of September 30, 2018 and December 31, 2017. Useful Life September 30, 2018 December 31, 2017 (in thousands) Computer equipment and software 3 $ 914 $ 630 Furniture and fixtures 5 845 800 Equipment 7 1,011 628 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 2,621 2,582 Office equipment under capital lease 3 114 36 5,505 4,676 Less accumulated depreciation (1,697 ) (1,059 ) Net property and equipment $ 3,808 $ 3,617 Depreciation expense, including expense associated with assets under capital leases, was approximately $0.2 million for each of the three months ended September 30, 2018 and 2017, and approximately $0.6 million and $0.4 million for the nine months ended September 30, 2018 and 2017, respectively.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2018
Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following provides a reconciliation of cash, cash equivalents, and restricted cash reported in the consolidated balance sheet that sum to the total of the amounts reported in the unaudited condensed consolidated statement of cash flows (in thousands): September 30, 2018 September 30, 2017 Cash and cash equivalents $ 162,430 $ 89,599 Other assets 1,566 1,281 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 163,996 $ 90,880
Summary of Property and Equipment and Related Accumulated Depreciation	The following is the summary of property and equipment and related accumulated depreciation as of September 30, 2018 and December 31, 2017. Useful Life September 30, 2018 December 31, 2017 (in thousands) Computer equipment and software 3 $ 914 $ 630 Furniture and fixtures 5 845 800 Equipment 7 1,011 628 Leasehold improvements Shorter of the useful life or remaining lease term (10 years) 2,621 2,582 Office equipment under capital lease 3 114 36 5,505 4,676 Less accumulated depreciation (1,697 ) (1,059 ) Net property and equipment $ 3,808 $ 3,617
ASC 606
Impact on Condensed Consolidated Balance Sheets as Result of Adopting ASC 606	The Company, as a result of adopting ASC 606 on January 1, 2018, has revised its comparative financial statements for the prior year as if ASC 606 had been effective for that period, as set forth below. December 31, 2017 (in thousands) As revised under ASC 606 As originally reported under ASC 605 Effect of change Short-term deferred revenue $ 81,667 $ 84,910 $ (3,243 ) Accumulated deficit $ (370,807 ) $ (374,050 ) $ 3,243

Strategic Collaborations and _2

Strategic Collaborations and Other Significant Agreements (Tables)	9 Months Ended
	Sep. 30, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Revenues Recognized From Strategic Collaboration Agreements	During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following revenues from its strategic collaboration agreements and had the following deferred revenue balances as of September 30, 2018: Three Months Ended September 30, Nine Months Ended September 30, 2018 2017 2018 2017 Collaboration Revenue: (in thousands) (in thousands) MTPC Agreement $ — $ — $ 9,281 $ — Otsuka U.S. Agreement 29,030 22,519 75,086 60,001 Otsuka International Agreement 24,114 18,764 63,176 30,667 Total Proportional Performance Revenue $ 53,144 $ 41,283 $ 147,543 $ 90,668 MTPC Stability Studies 25 — 349 — Total Collaboration Revenue $ 53,169 $ 41,283 $ 147,892 $ 90,668
Deferred Revenues Balance	During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following revenues from its strategic collaboration agreements and had the following deferred revenue balances as of September 30, 2018: September 30, 2018 Short-Term Long-Term Total Deferred Revenue: (in thousands) MTPC Agreement $ — $ — $ — Otsuka U.S. Agreement 41,152 43,669 84,821 Otsuka International Agreement 28,947 33,076 62,023 Vifor Agreement — 4,679 4,679 Total $ 70,099 $ 81,424 $ 151,523
Schedule of Changes In Contract Assets and Liabilities	The following table presents changes in the Company’s contract assets and liabilities during the nine months ended September 30, 2018 and 2017 (in thousands): Nine Months Ended September 30, 2018 Balance at Beginning of Period Additions Deductions Balance at End of Period Contract assets: Other current assets $ — $ 531 $ (531 ) $ — Accounts receivable (1) $ 34,186 $ 120,283 $ (153,938 ) $ 531 Contract liabilities Deferred revenue $ 179,624 $ 119,442 $ (147,543 ) $ 151,523 Accounts payable $ — $ 4,427 $ (1,040 ) $ 3,387 Nine Months Ended September 30, 2017 Contract assets - Accounts receivable $ 33,823 $ 9,138 $ (42,961 ) $ — Contract liabilities - Deferred revenue $ 197,289 $ 99,111 $ (90,668 ) $ 205,732 (1)
Schedule of Revenue Recognized Resulting from Changes in Contract Asset and Contract Liability	During the three and nine months ended September 30, 2018 and 2017, the Company recognized the following revenues as a result of changes in the contract asset and contract liability balances in the respective periods (in thousands): Three Months Ended September 30, Nine Months Ended September 30, Revenue Recognized in the Period from: 2018 2017 2018 2017 Amounts included in deferred revenue at the beginning of the period $ 53,144 $ 41,026 $ 110,974 $ 60,001 Performance obligations satisfied in previous periods $ — $ — $ 6,813 $ —

Available for Sale Securities (

Available for Sale Securities (Tables)	9 Months Ended
	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Available for Sale Securities at Fair Value	Available for sale securities at September 30, 2018 and December 31, 2017 consist of the following : Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) September 30, 2018 Cash and cash equivalents $ 162,430 $ — $ — $ 162,430 Available for sale securities: Certificates of deposit $ 445 $ — $ — $ 445 U.S. government debt securities 177,181 — (363 ) 176,818 Corporate debt securities 50,497 — (46 ) 50,451 Total available for sale securities $ 228,123 $ — $ (409 ) $ 227,714 Total cash, cash equivalents, and available for sale securities $ 390,553 $ — $ (409 ) $ 390,144 Gross Gross Unrealized Unrealized Amortized Cost Gains Losses Fair Value (in thousands) December 31, 2017 Cash and cash equivalents $ 70,156 $ — $ — $ 70,156 Available for sale securities: Certificates of deposit $ 14,117 $ — $ — $ 14,117 U.S. government debt securities 175,155 — (352 ) 174,803 Corporate debt securities 58,806 — (90 ) 58,716 Total available for sale securities $ 248,078 $ — $ (442 ) $ 247,636 Total cash, cash equivalents, and available for sale securities $ 318,234 $ — $ (442 ) $ 317,792
Estimated Fair Value of Available for Sale Securities by Contractual Maturity	The estimated fair value of the Company’s available for sale securities balance at September 30, 2018, by contractual maturity, is as follows: Due in one year or less $ 212,725 Due after one year 14,989 Total available for sale securities $ 227,714
Summary of Available for Sale Securities that were in Continuous Unrealized Loss Position	The following table summarizes the Company’s available for sale securities that were in a continuous unrealized loss position, but were not deemed to be other-than temporarily impaired, as of September 30, 2018 and December 31, 2017: Unrealized Loss for Less Than 12 Months Unrealized Loss for 12 Months or More Total Gross Gross Gross Unrealized Estimated Unrealized Estimated Unrealized Estimated Losses Fair Value Losses Fair Value Losses Fair Value (in thousands) September 30, 2018 Available for sale securities: U.S. government debt securities $ (342 ) $ 158,845 $ (21 ) $ 14,981 $ (363 ) $ 173,826 Corporate debt securities (38 ) 42,009 (8 ) 7,470 (46 ) 49,479 Total $ (380 ) $ 200,854 $ (29 ) $ 22,451 $ (409 ) $ 223,305 Unrealized Loss for Less Than 12 Months Unrealized Loss for 12 Months or More Total Gross Gross Gross Unrealized Estimated Unrealized Estimated Unrealized Estimated Losses Fair Value Losses Fair Value Losses Fair Value (in thousands) December 31, 2017 Available for sale securities: U.S. government debt securities $ (343 ) $ 170,812 $ (9 ) $ 3,991 $ (352 ) $ 174,803 Corporate debt securities (90 ) 58,716 — — (90 ) 58,716 Total $ (433 ) $ 229,528 $ (9 ) $ 3,991 $ (442 ) $ 233,519

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Assets Measured or Disclosed at Fair Value on Recurring Basis	Assets measured or disclosed at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 are summarized below: Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) September 30, 2018 Assets: Cash and cash equivalents $ 162,430 $ — $ — $ 162,430 Certificates of deposit — 445 — 445 U.S. government debt securities — 176,818 — 176,818 Corporate debt securities — 50,451 — 50,451 $ 162,430 $ 227,714 $ — $ 390,144 Fair Value Measurements Using Level 1 Level 2 Level 3 Total (in thousands) December 31, 2017 Assets: Cash and cash equivalents $ 70,156 $ — $ — $ 70,156 Certificates of deposit — 14,117 — 14,117 U.S. government debt securities — 174,803 — 174,803 Corporate debt securities — 58,716 — 58,716 $ 70,156 $ 247,636 $ — $ 317,792

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
	Sep. 30, 2018
Payables And Accruals [Abstract]
Components of Accrued Expenses	Accrued expenses as of September 30, 2018 and December 31, 2017 are as follows: September 30, 2018 December 31, 2017 (in thousands) Accrued clinical expenses $ 80,315 $ 43,297 Accrued bonus 3,481 3,388 Merger costs 2,084 — Professional fees 1,537 808 Accrued vacation 858 797 Accrued payroll 398 795 Accrued severance 40 — Income tax payable — 987 Accrued other 5,903 2,369 Total accrued expenses $ 94,616 $ 52,441

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2018
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: September 30, 2018 December 31, 2017 Common stock options and RSUs outstanding (1) 4,851,790 4,388,752 Shares available for issuance under the 2014 Plan (2) 3,347,957 1,790,600 Warrant to purchase common stock 509,611 509,611 Shares available for issuance under the ESPP (3) 603,522 652,290 Total 9,312,880 7,341,253 (1) (2) (3) On February 28, 2016, the shares reserved for future issuance under the ESPP increased by 273,404 shares pursuant to the ESPP Evergreen Provision. There were no increases in the shares reserved for future issuance subsequent to this period as the maximum aggregate number of shares available for purchase had reached its cap of 739,611.
Stock-Based Compensation Expense Related to Share-Based Awards	The Company has classified its stock-based compensation expense related to share-based awards as follows: Three Months Ended Nine Months Ended September 30, 2018 September 30, 2017 September 30, 2018 September 30, 2017 (in thousands) (in thousands) Research and development $ 647 $ 569 $ 2,090 $ 5,741 (1) General and administrative 1,605 1,584 4,888 4,346 Total $ 2,252 $ 2,153 $ 6,978 $ 10,087 (1)
Schedule of Compensation Expense by Type of Award	Compensation expense by type of award: Three Months Ended Nine Months Ended September 30, 2018 September 30, 2017 September 30, 2018 September 30, 2017 (in thousands) (in thousands) Stock options $ 1,458 $ 1,606 $ 5,074 $ 4,927 Restricted stock — 93 — 158 Restricted stock units 742 407 1,751 1,458 Employee stock purchase plan 52 47 153 131 Warrant — — — 3,413 Total $ 2,252 $ 2,153 $ 6,978 $ 10,087

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments Required Under Lease	At September 30, 2018, the Company’s future minimum payments required under this Lease are as follows: Operating Lease (in thousands) 2018 $ 896 2019 5,122 2020 5,325 2021 5,355 2022 4,997 Thereafter 18,991 Total $ 40,686

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2018
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: As of September 30, 2018 2017 Warrant 509,611 509,611 Outstanding stock options 3,957,940 3,743,303 Unvested restricted stock — 13,982 Unvested restricted stock units 893,850 728,438 Total 5,361,401 4,995,334

Nature of Organization and Op_2

Nature of Organization and Operations - Additional Information (Details) $ in Thousands	Jun. 28, 2018USD ($)shares	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Nature Of Organization And Operations [Line Items]
Cash, and cash equivalents, and available for sale securities | $		$ 390,144	$ 317,792
Number of months for operating plan sufficiently funded by cash resources		12 months
Merger Agreement
Nature Of Organization And Operations [Line Items]
Issued and outstanding common stock converted into right to receive shares, ratio	0.37433
Implied equity ownership in combined company, shareholders percentage	49.40%
Company or Keryx required to pay other party, termination fee | $	$ 22,000
Keryx | Merger Agreement
Nature Of Organization And Operations [Line Items]
Implied equity ownership in combined company, shareholders percentage	50.60%
Additional shares expected to be issued | shares	4,000,000
Keryx | Merger Agreement | Zero Coupon Convertible Senior Notes due 2021
Nature Of Organization And Operations [Line Items]
Debt instrument, due year	2,021
Keryx | Notes Conversion Agreement | Zero Coupon Convertible Senior Notes due 2021 | Common Stock
Nature Of Organization And Operations [Line Items]
Senior notes converted to stock | shares	35,582,335

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment			1
Recognized revenue under license agreement	$ 53,144,000	$ 41,026,000	$ 110,974,000	$ 60,001,000
Depreciation expense	200,000	$ 200,000	$ 600,000	400,000
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
Accounting Standards Update 2016-18
Summary Of Significant Accounting Policies [Line Items]
Relocation in restricted cash from cash used in operating activities to cash, cash equivalents, and restricted cash at beginning of period			$ 1,300,000	$ 1,300,000
Otsuka U.S. Agreement
Summary Of Significant Accounting Policies [Line Items]
Cost share costs for license agreement	200,000
Reimbursable by Otsuka	100,000
Cost share costs by partner for license agreement	500,000
Reimbursable to Otsuka	$ 100,000
Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement
Summary Of Significant Accounting Policies [Line Items]
Milestone revenue			10,000,000
Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | ASC 606
Summary Of Significant Accounting Policies [Line Items]
Recognized revenue under license agreement					$ 3,200,000
Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones
Summary Of Significant Accounting Policies [Line Items]
Milestone revenue			4,000,000
Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones | Maximum
Summary Of Significant Accounting Policies [Line Items]
Milestone revenue			10,000,000
Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones | ASC 606
Summary Of Significant Accounting Policies [Line Items]
Allocated arrangement consideration			$ 4,000,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Impact on Condensed Consolidated Balance Sheets as Result of Adopting ASC 606 (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Short-term deferred revenue	$ 70,099	$ 81,667
Accumulated deficit	$ (454,341)	(370,807)
As originally reported under ASC 605 | ASC 606
Summary Of Significant Accounting Policies [Line Items]
Short-term deferred revenue		84,910
Accumulated deficit		(374,050)
Effect of change | ASC 606
Summary Of Significant Accounting Policies [Line Items]
Short-term deferred revenue		(3,243)
Accumulated deficit		$ 3,243

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents	$ 162,430	$ 70,156	$ 89,599
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	163,996	$ 71,437	90,880	$ 188,616
Other Assets
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, noncurrent	$ 1,566		$ 1,281

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Property and Equipment and Related Accumulated Depreciation (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gross property, plant and equipment	$ 5,505	$ 4,676
Less accumulated depreciation	(1,697)	(1,059)
Net property and equipment	$ 3,808	3,617
Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	3 years
Gross property, plant and equipment	$ 914	630
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	5 years
Gross property, plant and equipment	$ 845	800
Equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Useful life	7 years
Gross property, plant and equipment	$ 1,011	628
Leasehold improvements
Property, Plant and Equipment [Line Items]
Leasehold improvements, Useful Life	Shorter of the useful life or remaining lease term (10 years)
Gross property, plant and equipment	$ 2,621	2,582
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	$ 114	$ 36

Strategic Collaborations and _3

Strategic Collaborations and Other Significant Agreements - Additional Information (Details)

May 12, 2017USD ($)

Apr. 25, 2017USD ($)

Feb. 09, 2017USD ($)$ / sharesshares

May 31, 2017USD ($)$ / sharesshares

Mar. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Sep. 30, 2018USD ($)shares

Sep. 30, 2017USD ($)

Mar. 31, 2017USD ($)

Jun. 30, 2018USD ($)

Sep. 30, 2018USD ($)Obligationshares

Sep. 30, 2017USD ($)

Dec. 31, 2017USD ($)shares

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

$ 53,169,000

$ 41,283,000

$ 147,892,000

$ 90,668,000

Deferred revenue

151,523,000

151,523,000

Deferred revenue, current

70,099,000

70,099,000

$ 81,667,000

Deferred revenue, noncurrent

$ 81,424,000

$ 81,424,000

$ 97,957,000

Common stock shares sold | shares

57,046,563

57,046,563

47,612,619

Accounts Payable

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue

$ 3,387,000

$ 3,387,000

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 0

Number of performance obligations | Obligation

3

Deferred revenue

84,821,000

$ 84,821,000

Collaborative arrangements cost sharing payments

$ 167,500,000

Percentage of market penetration for license agreement

90.00%

License agreement, notice period for termination

12 months

Transaction price

$ 326,300,000

Reimbursement for Otsuka's share of costs previously incurred

$ 33,800,000

Transaction price, description

As of September 30, 2018, the transaction price totaling $326.3 million is comprised of: (i) the up-front payment of $125.0 million, (ii) the cost share payment with respect to amounts incurred by the Company through December 31, 2016 of $33.8 million, and (iii) the estimate of the cost share payments to be received of approximately $167.5 million with respect to amounts incurred by the Company subsequent to December 31, 2016. As of September 30, 2018, no development or regulatory milestones have been assessed as probable of being reached and thus have been fully constrained.

Deferred revenue, current

41,152,000

$ 41,152,000

Deferred revenue, noncurrent

43,669,000

43,669,000

Cost share costs incurred

200,000

Reimbursable by Otsuka

100,000

Cost share costs incurred by partners

500,000

Reimbursable to Otsuka

100,000

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement | Accounts Payable

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue, current

1,900,000

1,900,000

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement | Development and Regulatory Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

0

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement | Up-front, Non-refundable and Non-creditable

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

$ 125,000,000

$ 125,000,000

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Number of performance obligations | Obligation

3

Deferred revenue

62,023,000

$ 62,023,000

Reimbursement for Otsuka's share of costs previously incurred

200,000

Transaction price

$ 249,300,000

Transaction price, description

As of September 30, 2018, the transaction price totaling $249.3 million is comprised of: (i) the up-front payment of $73.0 million, (ii) the cost share payment with respect to amounts incurred by the Company during the quarter ended March 31, 2017 of $0.2 million, and (iii) an estimate of the cost share payments to be received with respect to amounts incurred by the Company subsequent to March 31, 2017 of $176.1 million. As of September 30, 2018, no development or regulatory milestones have been assessed as probable of being reached and thus have been fully constrained.

Deferred revenue, current

28,947,000

$ 28,947,000

Deferred revenue, noncurrent

33,076,000

33,076,000

Estimate Subsequent Cost Share Payment Receivable

176,100,000

Milestone or royalty payments received

$ 0

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement | Accounts Payable

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Deferred revenue, current

1,500,000

1,500,000

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement | Development and Regulatory Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

0

Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement | Up-front, Non-refundable and Non-creditable

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

73,000,000

$ 73,000,000

Otsuka Pharmaceutical Company. Ltd. | Minimum | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Percentage of increase in funding to fund current global development costs

52.50%

Reduction in percentage of future payments due upon current global development costs creditable

50.00%

Percentage of remaining creditable amount applied to future payments

50.00%

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Percentage of increase in funding to fund current global development costs

80.00%

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize United States Collaboration and License Agreement | Commercial Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 575,000,000

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize United States Collaboration and License Agreement | Development Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

125,000,000

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize United States Collaboration and License Agreement | Regulatory Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

65,000,000

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize International Collaboration and License Agreement | Commercial Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

525,000,000

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize International Collaboration and License Agreement | Development Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

80,000,000

Otsuka Pharmaceutical Company. Ltd. | Maximum | Development and Commercialize International Collaboration and License Agreement | Regulatory Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

52,000,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Development costs incurred

$ 20,500,000

Expected additional development costs

0

Expected reimbursement for development costs

$ 500,000

Collaboration Agreement, expiration period

10 years

Collaboration Agreement, notice period for termination

12 months

Milestone revenue

$ 10,000,000

Additional milestone or royalty payments received

$ 0

Number of performance obligations | Obligation

2

Cost of research services

$ 20,500,000

Deferred revenue

0

0

Accounts receivable

500,000

500,000

Unbilled accounts receivables

500,000

500,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Upfront

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

20,000,000

Incurred clinical and commercial development cost

20,000,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development, Regulatory and Commercial Events

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

225,000,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

4,000,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Regulatory Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

0

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones One

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

6,000,000

Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement | Development Milestones Two

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

4,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

265,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Development and Regulatory Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

50,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Commercial Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 175,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Development, Regulatory and Sales Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Percentage of royalty payments on sales

20.00%

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Development Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 10,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Regulatory Milestone Payments

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Upfront cash payment received

40,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | Development and Commercialize Collaboration Agreement | Sales Milestones

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

175,000,000

Mitsubishi Tanabe Pharma Corporation | Maximum | New Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Data access fee receivable

25,000,000

25,000,000

Janssen Pharmaceutica NV | Development and Commercialize Research and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 215,000,000

Collaboration Agreement, expiration period

10 years

Collaboration Agreement, notice period for termination

180 days

Upfront cash payment received

$ 16,500,000

Upfront payment made in cash

$ 1,000,000

Warrant to purchase common stock, shares | shares

509,611

Johnson & Johnson Innovation | Development and Commercialize Research and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Warrant to purchase common stock, shares | shares

509,611

Fair value of warrant

$ 3,400,000

$ 3,400,000

Exercise price | $ / shares

$ 9.81

Vifor (International) Ltd. | License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Milestone revenue

$ 20,000,000

$ 20,000,000

License agreement, notice period for termination

12 months

Deferred revenue, noncurrent

$ 4,700,000

Common stock shares sold | shares

3,571,429

Sale of stock, price per share | $ / shares

$ 14

Proceeds from common stock sold

$ 50,000,000

Premium over the closing stock price of common stock | $ / shares

$ 12.69

Premium amount over the closing stock price of common stock

$ 4,700,000

Global Development Plan | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Reimbursement for Otsuka's share of costs previously incurred

$ 33,800,000

Global Development Plan | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Reimbursement for Otsuka's share of costs previously incurred

$ 200,000

Global Development Plan | Otsuka Pharmaceutical Company. Ltd. | Minimum | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Collaborative arrangements cost sharing payments

167,500,000

Global Development Plan | Otsuka Pharmaceutical Company. Ltd. | Minimum | Development and Commercialize International Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Estimate Subsequent Cost Share Payment Receivable

$ 176,100,000

Collaboration Revenue

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

53,169,000

41,283,000

147,892,000

90,668,000

Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd.

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

53,100,000

Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

29,030,000

22,519,000

75,086,000

60,001,000

Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

24,114,000

18,764,000

63,176,000

30,667,000

Collaboration Revenue | Mitsubishi Tanabe Pharma Corporation and Otsuka Pharmaceutical Company Limited

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

53,144,000

41,283,000

147,543,000

90,668,000

Collaboration Revenue | Mitsubishi Tanabe Pharma Corporation

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

9,281,000

Collaboration Revenue | Mitsubishi Tanabe Pharma Corporation | Development and Commercialize Collaboration Agreement

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

0

$ 0

9,300,000

$ 0

Collaboration Revenue | Clinical and Regulatory Activities

Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]

Recognized revenue under license agreement

$ 25,000

$ 349,000

Strategic Collaborations and _4

Strategic Collaborations and Other Significant Agreements - Revenues Recognized From Strategic Collaboration Agreements (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Collaboration Revenue:
Collaboration revenue	$ 53,169,000	$ 41,283,000	$ 147,892,000	$ 90,668,000
Collaboration Revenue
Collaboration Revenue:
Collaboration revenue	53,169,000	41,283,000	147,892,000	90,668,000
Collaboration Revenue | Mitsubishi Tanabe Pharma Corporation
Collaboration Revenue:
Collaboration revenue			9,281,000
Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd.
Collaboration Revenue:
Collaboration revenue	53,100,000
Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize United States Collaboration and License Agreement
Collaboration Revenue:
Collaboration revenue	29,030,000	22,519,000	75,086,000	60,001,000
Collaboration Revenue | Otsuka Pharmaceutical Company. Ltd. | Development and Commercialize International Collaboration and License Agreement
Collaboration Revenue:
Collaboration revenue	24,114,000	18,764,000	63,176,000	30,667,000
Collaboration Revenue | Mitsubishi Tanabe Pharma Corporation and Otsuka Pharmaceutical Company Limited
Collaboration Revenue:
Collaboration revenue	53,144,000	$ 41,283,000	147,543,000	$ 90,668,000
Collaboration Revenue | Clinical and Regulatory Activities
Collaboration Revenue:
Collaboration revenue	$ 25,000		$ 349,000

Strategic Collaborations and _5

Strategic Collaborations and Other Significant Agreements - Deferred Revenues Balance (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Deferred Revenue:
Short-Term	$ 70,099	$ 81,667
Long-Term	81,424	$ 97,957
Total	151,523
Otsuka Pharmaceutical Company. Ltd. | U.S.
Deferred Revenue:
Short-Term	41,152
Long-Term	43,669
Total	84,821
Otsuka Pharmaceutical Company. Ltd. | International
Deferred Revenue:
Short-Term	28,947
Long-Term	33,076
Total	62,023
Vifor Pharma
Deferred Revenue:
Long-Term	4,679
Total	$ 4,679

Strategic Collaborations and _6

Strategic Collaborations and Other Significant Agreements - Schedule of Changes In Contract Assets and Liabilities (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, Balance at End of Period		$ 151,523
Other Current Assets
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets, Additions		531
Contract assets, Deductions		(531)
Accounts Receivable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets, Balance at Beginning of Period		34,186	[1]	$ 33,823
Contract assets, Additions		120,283	[1]	9,138
Contract assets, Deductions		(153,938)	[1]	(42,961)
Contract assets, Balance at End of Period	[1]	531
Deferred Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, Balance at Beginning of Period		179,624		197,289
Contract liabilities, Additions		119,442		99,111
Contract liabilities, Deductions		(147,543)		(90,668)
Contract liabilities, Balance at End of Period		151,523		$ 205,732
Accounts Payable
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract liabilities, Additions		4,427
Contract liabilities, Deductions		(1,040)
Contract liabilities, Balance at End of Period		$ 3,387
[1]	Excludes accounts receivable from other services related to clinical and regulatory activities performed by the Company on behalf of MTPC that are not included in the performance obligations identified under the MTPC Agreement. These receivables represented approximately $157,000 and $30,000 of accounts receivables in the accompanying unaudited condensed consolidated balance sheet as of September 30, 2018 and the audited consolidated balance sheet as of December 31, 2017, respectively.

Strategic Collaborations and _7

Strategic Collaborations and Other Significant Agreements - Schedule of Changes In Contract Assets and Liabilities (Parenthetical) (Details) - Accounts Receivable - USD ($)	Sep. 30, 2018		Dec. 31, 2017		Dec. 31, 2016
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets - Accounts receivable	$ 531,000	[1]	$ 34,186,000	[1]	$ 33,823,000
Other Services Related to Clinical and Regulatory Activities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contract assets - Accounts receivable	$ 157,000		$ 30,000
[1]	Excludes accounts receivable from other services related to clinical and regulatory activities performed by the Company on behalf of MTPC that are not included in the performance obligations identified under the MTPC Agreement. These receivables represented approximately $157,000 and $30,000 of accounts receivables in the accompanying unaudited condensed consolidated balance sheet as of September 30, 2018 and the audited consolidated balance sheet as of December 31, 2017, respectively.

Strategic Collaborations and _8

Strategic Collaborations and Other Significant Agreements - Schedule of Revenue Recognized Resulting from Changes in Contract Asset and Contract Liability (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Amounts included in deferred revenue at the beginning of the period	$ 53,144	$ 41,026	$ 110,974	$ 60,001
Performance obligations satisfied in previous periods			$ 6,813

Available for Sale Securities -

Available for Sale Securities - Summary of Available for Sale Securities at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 228,123	$ 248,078
Gross Unrealized Losses	(409)	(442)
Fair Value	227,714	247,636
Cash and cash equivalents	162,430	70,156	$ 89,599
Cash and cash equivalents, Fair Value	162,430	70,156
Total cash, cash equivalents, and available for sale securities - Amortized Cost	390,553	318,234
Total cash, cash equivalents, and available for sale securities - Fair Value	390,144	317,792
U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	177,181	175,155
Gross Unrealized Losses	(363)	(352)
Fair Value	176,818	174,803
Certificates of deposit
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	445	14,117
Fair Value	445	14,117
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	50,497	58,806
Gross Unrealized Losses	(46)	(90)
Fair Value	$ 50,451	$ 58,716

Available for Sale Securities_2

Available for Sale Securities - Estimated Fair Value of Available for Sale Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Due in one year or less	$ 212,725
Due after one year	14,989
Total available for sale securities	$ 227,714	$ 247,636

Available for Sale Securities_3

Available for Sale Securities - Additional Information (Details)	9 Months Ended
	Sep. 30, 2018USD ($)Security	Sep. 30, 2017USD ($)	Dec. 31, 2017Security
Investments Debt And Equity Securities [Abstract]
Gains (losses) on available for sale securities | $	$ 0	$ 0
Available-for-sale, securities in unrealized loss position, number of securities | Security	49		60

Available for Sale Securities_4

Available for Sale Securities - Summary of Available for Sale Securities that were in Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Unrealized Loss for Less Than 12 Months, Grosss Unrealized Losses	$ (380)	$ (433)
Unrealized Loss for Less Than 12 Months, Estimated Fair Value	200,854	229,528
Unrealized Loss for 12 Months or More, Gross Unrealized Losses	(29)	(9)
Unrealized Loss for 12 Months or More, Estimated Fair Value	22,451	3,991
Total, Gross Unrealized Losses	(409)	(442)
Total, Estimated Fair Value	223,305	233,519
U.S. government debt securities
Schedule Of Available For Sale Securities [Line Items]
Unrealized Loss for Less Than 12 Months, Grosss Unrealized Losses	(342)	(343)
Unrealized Loss for Less Than 12 Months, Estimated Fair Value	158,845	170,812
Unrealized Loss for 12 Months or More, Gross Unrealized Losses	(21)	(9)
Unrealized Loss for 12 Months or More, Estimated Fair Value	14,981	3,991
Total, Gross Unrealized Losses	(363)	(352)
Total, Estimated Fair Value	173,826	174,803
Corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Unrealized Loss for Less Than 12 Months, Grosss Unrealized Losses	(38)	(90)
Unrealized Loss for Less Than 12 Months, Estimated Fair Value	42,009	58,716
Unrealized Loss for 12 Months or More, Gross Unrealized Losses	(8)
Unrealized Loss for 12 Months or More, Estimated Fair Value	7,470
Total, Gross Unrealized Losses	(46)	(90)
Total, Estimated Fair Value	$ 49,479	$ 58,716

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Assets Measured or Disclosed at Fair Value on Recurring Basis (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, Fair Value	$ 162,430,000	$ 70,156,000
Assets Measured at fair value on recurring basis	212,725,000
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]
Cash and cash equivalents, Fair Value	162,430,000	70,156,000
Assets Measured at fair value on recurring basis	390,144,000	317,792,000
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	445,000	14,117,000
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	176,818,000	174,803,000
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	50,451,000	58,716,000
Fair value measurements recurring | Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash and cash equivalents, Fair Value	162,430,000	70,156,000
Assets Measured at fair value on recurring basis	162,430,000	70,156,000
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	227,714,000	247,636,000
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	445,000	14,117,000
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	176,818,000	174,803,000
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	$ 50,451,000	$ 58,716,000

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Details) - Level 3 - USD ($)	Sep. 30, 2018	Dec. 31, 2017
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	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued clinical expenses	$ 80,315	$ 43,297
Accrued bonus	3,481	3,388
Merger costs	2,084
Professional fees	1,537	808
Accrued vacation	858	797
Accrued payroll	398	795
Accrued severance	40
Income tax payable		987
Accrued other	5,903	2,369
Total accrued expenses	$ 94,616	$ 52,441

Warrant - Additional Informatio

Warrant - Additional Information (Details) - Janssen Agreement - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2018	Feb. 28, 2017
Class Of Warrant Or Right [Line Items]
Warrant to purchase common stock, shares		509,611
Exercise price		$ 9.81
Fair value of warrant at issuance	$ 3.4
Warrant expiration date	Feb. 9, 2022

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details)	Feb. 28, 2018shares	Dec. 23, 2013USD ($)$ / sharesshares	Mar. 31, 2018USD ($)$ / sharesshares	May 31, 2016USD ($)	Sep. 30, 2018USD ($)$ / sharesshares	Mar. 31, 2018USD ($)$ / sharesshares	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2018USD ($)Installment$ / sharesshares	Sep. 30, 2017USD ($)shares	Feb. 28, 2014shares
Class of Stock [Line Items]
Common stock, shares authorized					175,000,000			175,000,000	175,000,000
Common stock, par value | $ / shares					$ 0.00001			$ 0.00001	$ 0.00001
Common stock, shares issued					57,046,563			47,612,619	57,046,563
Common stock, shares outstanding					57,046,563			47,612,619	57,046,563
Preferred stock, shares authorized					25,000,000			25,000,000	25,000,000
Preferred stock, par value | $ / shares					$ 0.00001			$ 0.00001	$ 0.00001
Preferred stock, shares issued					0			0	0
Preferred stock, shares outstanding					0			0	0
Proceeds from the issuance of common stock, net of issuance costs | $									$ 95,453,000	$ 109,541,000
Common stock, shares reserved for future issuance					9,312,880			7,341,253	9,312,880
Stock-based compensation expense | $					$ 2,252,000		$ 2,153,000		$ 6,978,000	10,087,000
Inducement Award Program
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued					750,000				750,000
Granted, Shares									255,550
Outstanding, Shares					249,550				249,550
Inducement Award Program | Employees
Class of Stock [Line Items]
Granted, Shares									255,550
Restricted Stock Units
Class of Stock [Line Items]
Granted shares of restricted stock	367,250
Stock-based compensation expense | $					$ 742,000		407,000		$ 1,751,000	1,458,000
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	522,200
Stock-based compensation description									Options granted by the Company vest over periods of between 12 and 48 months, subject, in each case, to the individual’s continued service through the applicable vesting date. Options vest either 100% on the first anniversary of the grant date or in installments of (i) 25% at the one year anniversary and (ii) 12 equal quarterly installments beginning on the first day of each calendar quarter after the one year anniversary of the grant date, subject to the individual’s continuous service with the Company.
Options expiration after the date of grant									10 years
Stock-based compensation expense | $					1,458,000		1,606,000		$ 5,074,000	4,927,000
Stock Options | Share-based Compensation Award, Tranche, First Anniversary of Grant Date
Class of Stock [Line Items]
Vesting percentage									100.00%
Stock Options | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting periods									1 year
Vesting percentage									25.00%
Stock Options | Share Based Compensation Award Tranche Two
Class of Stock [Line Items]
Number of equal quarterly installments | Installment									12
Restricted Stock
Class of Stock [Line Items]
Granted shares of restricted stock									0
Stock-based compensation expense | $					$ 0		93,000		$ 0	$ 158,000
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares		$ 7.42
Grant-date fair value of restricted stock issued | $		$ 3,900,000
Restricted Stock | Employees
Class of Stock [Line Items]
Granted shares of restricted stock		450,224
Restricted Stock | Non Employees
Class of Stock [Line Items]
Granted shares of restricted stock		79,067
Common Stock | Follow-on public offering
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares			8,500,000
Proceeds from the issuance of common stock, net of issuance costs | $			$ 84,800,000
Sale of stock, price per share | $ / shares			$ 10.50			$ 10.50
Maximum | Restricted Stock Units
Class of Stock [Line Items]
Vesting periods									3 years
Maximum | Stock Options
Class of Stock [Line Items]
Vesting periods									48 months
Minimum | Restricted Stock Units
Class of Stock [Line Items]
Vesting periods									1 year
Minimum | Stock Options
Class of Stock [Line Items]
Vesting periods									12 months
At The Market Equity Offering Program | Common Stock
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares						694,306		1,080,908	0	150,023
Proceeds from the issuance of common stock, net of issuance costs | $						$ 10,500,000		$ 12,100,000		$ 1,600,000
At The Market Equity Offering Program | Maximum
Class of Stock [Line Items]
Common stock sales agreement amount | $				$ 75,000,000
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance					3,347,957			1,790,600	3,347,957		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									522,200
2014 Plans | Director
Class of Stock [Line Items]
Granted, Shares									112,500
2014 Plans | Restricted Stock Units | Employees
Class of Stock [Line Items]
Granted shares of restricted stock									372,250
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									48,768
Stock-based compensation expense | $					$ 52,000		$ 47,000		$ 200,000	$ 100,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Details) - shares	Sep. 30, 2018	Dec. 31, 2017	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	9,312,880	7,341,253
Warrant To Purchase Common Stock
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	509,611	509,611
Stock Options and Restricted Stock Units
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	4,851,790	4,388,752
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	3,347,957	1,790,600	1,785,000
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares reserved for future issuance	603,522	652,290

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Reserved Shares of Common Stock for Future Issuance (Parenthetical) (Details) - shares	Jan. 01, 2018	Jan. 01, 2017	Feb. 28, 2016	Jan. 01, 2016	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Feb. 28, 2014
Class of Stock [Line Items]
Common stock, shares reserved for future issuance					9,312,880		7,341,253
2014 Plans
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance	1,575,329	1,265,863		986,800
Common stock, shares reserved for future issuance					3,347,957		1,790,600	1,785,000
Inducement Award Program | Scenario, Forecast
Class of Stock [Line Items]
Common stock, shares reserved for future issuance						750,000
Employee Stock Purchase Plan
Class of Stock [Line Items]
Increase in common stock, shares reserved for future issuance			273,404		0
Common stock, shares reserved for future issuance					603,522		652,290
Maximum aggregate number of shares available for purchase			739,611

Stockholders Equity - Stock-Bas

Stockholders Equity - Stock-Based Compensation Expense Related to Share-Based Awards (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,252	$ 2,153	$ 6,978	$ 10,087
Research and Development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	647	569	2,090	5,741	[1]
General and Administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,605	$ 1,584	$ 4,888	$ 4,346
[1]	This amount includes $3.4 million of fair value related to the warrant issued to Janssen.

Stockholders Equity - Stock-B_2

Stockholders Equity - Stock-Based Compensation Expense Related to Share-Based Awards (Parenthetical) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2017USD ($)
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value related to warrant	$ 3,413
Janssen Agreement
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Fair value related to warrant	$ 3,400

Stockholders Equity - Schedule

Stockholders Equity - Schedule of Compensation Expense by Type of Award (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 2,252,000	$ 2,153,000	$ 6,978,000	$ 10,087,000
Warrant
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense				3,413,000
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,458,000	1,606,000	5,074,000	4,927,000
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	0	93,000	0	158,000
Restricted Stock Units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	742,000	407,000	1,751,000	1,458,000
Employee Stock Purchase Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 52,000	$ 47,000	$ 153,000	$ 131,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Line Items]
Income tax provisions or benefits	$ 0		$ 0	$ 0	$ 0
Alternative minimum tax payable	0			$ 0		$ 800,000
Alternative minimum tax paid		$ 800,000
Alternative minimum tax receivable						$ 800,000
Federal tax at statutory rate				21.00%		35.00%
Tax Cuts and Jobs Act of 2017 change in tax rate reduction in deferred tax asset and corresponding valuation allowance						$ 43,000,000
Other Assets
Income Tax Disclosure [Line Items]
Alternative minimum tax receivable	$ 800,000			$ 800,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	1 Months Ended			3 Months Ended		9 Months Ended
	May 31, 2018USD ($)	Apr. 30, 2018USD ($)ft²	Jul. 31, 2016USD ($)ft²	Sep. 30, 2018USD ($)Extension_Option	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Extension_Option	Sep. 30, 2017USD ($)	Mar. 31, 2018USD ($)
Commitments And Contingencies [Line Items]
Landlord contributions accounted for deferred lease incentive		$ 3,289,170
Landlord contribution for leasehold improvements		1,142,010
Rent expense associated with lease				$ 800,000	$ 800,000	$ 2,400,000	$ 2,400,000
Contract cost incurred in research and development activities						110,400,000
Total remaining contract costs				162,900,000		162,900,000
Letter of Credit | Other Current Assets
Commitments And Contingencies [Line Items]
Increase (decrease) in security deposit in connection with lease	$ (200,000)	500,000
Total security deposit in connection with lease		$ 1,800,000		$ 1,600,000		$ 1,600,000		$ 1,300,000
Office Space
Commitments And Contingencies [Line Items]
Lease expiration date						Sep. 11, 2026
Lease period, number of extension options | Extension_Option				1		1
Lease extension period				5 years		5 years
Lab Space
Commitments And Contingencies [Line Items]
Lease expiration date						Nov. 30, 2021
Lease period, number of extension options | Extension_Option				1		1
Lease extension period				2 years		2 years
Lease Amendment
Commitments And Contingencies [Line Items]
Area of property leased | ft²		65,167
Third Amendment to Lease
Commitments And Contingencies [Line Items]
Area of property leased | ft²			45,362
Monthly lease payments			$ 242,000
Operating lease payments commencement date			Jan. 1, 2017
Lease Monthly Payments On Or About January 1 2017
Commitments And Contingencies [Line Items]
Monthly lease payments			$ 22,000
Fifth Amendment to Lease | Office Space
Commitments And Contingencies [Line Items]
Area of property leased | ft²		19,805
Monthly lease payments		$ 135,000
Operating lease payments commencement date		Feb. 1, 2019
Leased property delivered, date		2018-09
Leased property subject to annual rent escalations, commencement date		2019-09

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments Required Under Lease (Details) $ in Thousands	Sep. 30, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease, 2018	$ 896
Operating Lease, 2019	5,122
Operating Lease, 2020	5,325
Operating Lease, 2021	5,355
Operating Lease, 2022	4,997
Operating Lease, Thereafter	18,991
Operating Lease, Total	$ 40,686

Employee Retirement Plan - Addi

Employee Retirement Plan - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Employers contributions to defined contribution plan	$ 41,000	$ 27,000	$ 300,000	$ 200,000
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	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	5,361,401	4,995,334
Warrant
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	509,611	509,611
Outstanding Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	3,957,940	3,743,303
Unvested Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share		13,982
Unvested Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from calculation of diluted net loss per share	893,850	728,438