Agios Pharmaceuticals (AGIO) 10-Q 4 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 30, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	AGIOS PHARMACEUTICALS INC
Trading Symbol	AGIO
Entity Central Index Key	1,439,222
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		57,605,621

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 364,469	$ 102,724
Marketable securities	417,981	321,212
Collaboration receivable – related party	3,512	2,448
Royalty receivable – related party	1,417	1,222
Prepaid expenses and other current assets	15,614	17,655
Total current assets	802,993	445,261
Marketable securities	212,297	143,814
Property and equipment, net	23,732	24,431
Other non-current assets	1,104	891
Total assets	1,040,126	614,397
Current liabilities:
Accounts payable	17,932	22,767
Accrued expenses	17,005	34,031
Deferred revenue – related party	39,212	37,842
Deferred rent	550	301
Total current liabilities	74,699	94,941
Deferred revenue, net of current portion – related party	81,831	125,798
Deferred rent, net of current portion	18,002	18,155
Total liabilities	174,532	238,894
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized; no shares issued or outstanding at March 31, 2018 and December 31, 2017	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized; 57,541,613 and 48,826,153 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	58	49
Additional paid-in capital	1,717,609	1,174,904
Accumulated other comprehensive loss	(2,643)	(1,389)
Accumulated deficit	(849,430)	(798,061)
Total stockholders’ equity	865,594	375,503
Total liabilities and stockholders’ equity	$ 1,040,126	$ 614,397

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued (in shares)	57,541,613	48,826,153
Common stock, shares outstanding (in shares)	57,541,613	48,826,153

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Collaboration revenue – related party	$ 7,345	$ 10,508
Royalty revenue – related party	1,417	0
Total revenue	8,762	10,508
Operating expenses:
Research and development (net of $2,776 and $8,794 of cost reimbursement from related party for the three months ended March 31, 2017 and 2016, respectively)	78,224	62,732
General and administrative	24,550	14,823
Total operating expenses	102,774	77,555
Loss from operations	(94,012)	(67,047)
Interest income	3,187	881
Net loss	$ (90,825)	$ (66,166)
Net loss per share – basic and diluted (usd per share)	$ (1.63)	$ (1.56)
Weighted-average number of common shares used in computing net loss per share – basic and diluted (in shares)	55,694,603	42,280,525

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Reduction of research and development expenses	$ 0	$ 2,776

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (90,825)	$ (66,166)
Other comprehensive (loss) income
Unrealized (loss) gain on available-for-sale securities	(1,254)	101
Comprehensive loss	$ (92,079)	$ (66,065)

Condensed Consolidated Stateme7

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net loss	$ (90,825)	$ (66,166)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,725	1,591
Stock-based compensation expense	14,522	10,734
Net amortization of premium and discounts on investments	(406)	163
Loss on disposal of property and equipment	0	40
Changes in operating assets and liabilities:
Collaboration receivable – related party	(1,064)	(6,379)
Royalty receivable – related party	(195)	0
Tenant improvement and other receivables	0	(24)
Prepaid expenses and other current and non-current assets	1,901	(3,425)
Accounts payable	(4,469)	(994)
Accrued expenses	(17,144)	(6,889)
Deferred revenue – related party	(3,141)	(1,924)
Deferred rent	96	(801)
Net cash used in operating activities	(99,000)	(74,074)
Investing activities
Purchases of marketable securities	(330,971)	(26,740)
Proceeds from maturities and sales of marketable securities	164,871	136,585
Purchases of property and equipment	(1,432)	(293)
Net cash (used in) provided by investing activities	(167,532)	109,552
Financing activities
Payment of public offering costs, net of reimbursements	(188)	(100)
Proceeds from public offering of common stock, net of commissions	516,206	0
Net proceeds from stock option exercises and employee stock purchase plan	12,259	4,146
Net cash provided by financing activities	528,277	4,046
Net change in cash and cash equivalents	261,745	39,524
Cash and cash equivalents at beginning of the period	102,724	160,754
Cash and cash equivalents at end of the period	364,469	200,278
Supplemental disclosure of non-cash investing and financing transactions
Additions to property and equipment in accounts payable and accrued expenses	605	213
Proceeds from stock option exercises in other current assets	73	6
Public offering costs in accounts payable and accrued expenses	0	329
Public offering costs in accounts payable and accrued expenses	$ 158	$ 0

Overview and Basis of Presentat

Overview and Basis of Presentation	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Overview and Basis of Presentation	Overview and Basis of Presentation References to Agios Throughout this Quarterly Report on Form 10-Q, “we,” “us,” and “our,” and similar expressions, except where the context requires otherwise, refer to Agios Pharmaceuticals, Inc. and its consolidated subsidiaries, and “our Board of Directors” refers to the board of directors of Agios Pharmaceuticals, Inc. Overview We are a biopharmaceutical company committed to the fundamental transformation of patients’ lives through scientific leadership in the field of cellular metabolism, with the goal of making transformative, first- or best-in-class medicines. Our therapeutic areas of focus are cancer and rare genetic diseases, or RGDs, which are diseases that are directly caused by changes in genes or chromosomes, often passed from one generation to the next. Most RGDs are often associated with severe or life-threatening features. The incidence of a single RGD can vary widely but is generally very infrequent, usually equal to or less than one per 100,000 births. In both areas of cancer and RGDs, we are seeking to unlock the biology of cellular metabolism as a platform to create transformative therapies. We are located in Cambridge, Massachusetts. Basis of presentation The condensed consolidated balance sheet as of March 31, 2018 , and the condensed consolidated statements of operations, comprehensive loss, and cash flows for the three months ended March 31, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of our management, reflect all adjustments, which include only normal recurring adjustments, necessary to fairly state our financial position as of March 31, 2018 , and our results of operations and cash flows for the three months ended March 31, 2018 and 2017 . The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three -month period are also unaudited. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The year-end condensed consolidated balance sheet data was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. Accordingly, the condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2017 that was filed with the Securities and Exchange Commission, or the SEC, on February 14, 2018 . Our consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, Agios Securities Corporation, Agios International Sarl, and Agios Limited. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. GAAP. Liquidity In January 2018 , we completed a public offering of 7,089,553 shares of common stock at an offering price of $67.00 per share. We received net proceeds from this offering of $448.9 million , after deducting underwriting discounts and commissions paid by us. In addition, we granted the underwriters the right to purchase up to an additional 1,063,433 shares of common stock, which was exercised in January 2018 , resulting in additional net proceeds to us of $67.3 million , after underwriting discounts and commissions. After giving effect to the full exercise of the over-allotment option, the number of shares sold by us in the public offering totaled 8,152,986 shares, and net proceeds to us totaled $516.2 million , after underwriting discounts and commissions. As of March 31, 2018 , we had cash, cash equivalents and marketable securities of $994.7 million . Although we have incurred recurring losses and expect to continue to incur losses for the foreseeable future, we expect our cash, cash equivalents and marketable securities will be sufficient to fund current operations for at least the next twelve months from the issuance date of these financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Recent Accounting Pronouncements	Summary of Significant Accounting Policies and Recent Accounting Pronouncements Significant accounting policies Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , or ASU 2014-09. ASU 2014-09 was codified as Accounting Standards Codification, or ASC, 606, Revenue from Contracts with Customers , or ASC 606. Subsequently, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606) , which adjusted the effective date of ASU 2014-09; ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net) , which amends the principal-versus-agent implementation guidance and illustrations in ASU 2014-09; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies identifying performance obligations and licensing implementation guidance and illustrations in ASU 2014-09; ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , which addresses implementation issues and is intended to reduce the cost and complexity of applying the new revenue standard in ASU 2014-09; ASU No. 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (SEC Update) , which codifies recent announcements by the SEC staff; and ASU No. 2017-14, Income Statement—Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606) (SEC Update) , which codifies SEC Release 33-10403, or collectively with ASU 2014-09, the Revenue ASUs. We were required to adopt the Revenue ASUs effective January 1, 2018. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). We adopted the new standard under the modified retrospective method. In adopting the Revenue ASUs, we applied the practical expedient that permits aggregating the effect of all modifications that occurred prior to January 1, 2018. No other practical expedients were used. Upon finalization of our assessment, which resulted in changes to our estimates as of December 31, 2017, the impact of the cumulative effect of the accounting changes upon the adoption of the standard (in thousands) is as follows: December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue – related party, current and net of current portions $ 163,640 $ (39,456 ) $ 124,184 Accumulated deficit (798,061 ) 39,456 (758,605 ) The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements for the three months ended March 31, 2018 (in thousands, except per share data): Condensed Consolidated Balance Sheets March 31, 2018 Under Topic Under Topic Effect of Deferred revenue – related party $ 39,212 $ 35,396 $ 3,816 Deferred revenue, net of current portion – related party 81,831 122,060 (40,229 ) Accumulated deficit (849,430 ) (885,843 ) 36,413 Condensed Consolidated Statements of Operations Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Collaboration revenue – related party $ 7,345 $ 9,977 $ (2,632 ) Research and development expense 78,224 77,813 411 Total operating expenses 102,774 102,363 411 Loss from operations (94,012 ) (90,969 ) (3,043 ) Net loss (90,825 ) (87,782 ) (3,043 ) Net loss per share – basic and diluted (1.63 ) (1.58 ) (0.05 ) Condensed Consolidated Statements of Comprehensive Loss Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Comprehensive loss (92,079 ) (89,036 ) (3,043 ) Condensed Consolidated Statements of Cash Flows Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Adjustments to reconcile net loss to net cash used in operating activities: Deferred revenue – related party (3,141 ) (6,184 ) 3,043 Recent accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), or ASU 2016-02, which establishes principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing and uncertainty of cash flows arising from a lease. ASU 2016-02 was codified as ASC 842, Leases . Subsequently, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (SEC Update) , which codifies recent announcements by the SEC staff; and ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 , which provides a transition practical expedient for existing or expired land easements, or collectively with ASU 2016-02, the Leases ASUs. We will adopt ASC 842 effective January 1, 2019. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements We record cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our own assumptions (unobservable inputs). The hierarchy consists of three levels: Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, directly or indirectly, for substantially the full term of the asset or liability. Level 3 – Unobservable inputs that reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date. The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of March 31, 2018 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 262,897 $ 84,827 $ — $ 347,724 Marketable securities: Certificates of deposit — 5,226 — 5,226 U.S. Treasuries — 179,580 — 179,580 Government securities — 128,968 — 128,968 Corporate debt securities — 316,504 — 316,504 Total cash equivalents and marketable securities $ 262,897 $ 715,105 $ — $ 978,002 Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third-party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches, and observable market inputs to determine value. After completing our validation procedures, we did not adjust or override any fair value measurements provided by the pricing services as of March 31, 2018 . There have been no changes to the valuation methods during the three months ended March 31, 2018 . We evaluate transfers between levels at the end of each reporting period. There were no transfers between Level 1 and Level 2 during the three months ended March 31, 2018 . We have no financial assets or liabilities that were classified as Level 3 at any point during the three months ended March 31, 2018 .

Marketable Securities

Marketable Securities	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities Our marketable securities are classified as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities , and are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive loss in stockholders’ equity and a component of total comprehensive loss in the condensed consolidated statements of comprehensive loss , until realized. Realized gains and losses are included in investment income on a specific-identification basis. There were no realized gains or losses on marketable securities for the three months ended March 31, 2018 and 2017 and, as a result, there were no reclassifications of any amounts out of accumulated other comprehensive loss for those periods. Marketable securities at March 31, 2018 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 4,760 $ — $ (8 ) $ 4,752 U.S Treasuries 144,849 — (209 ) 144,640 Government securities 71,773 — (141 ) 71,632 Corporate debt securities 197,334 — (377 ) 196,957 Non-current: Certificates of deposit 480 — (6 ) 474 U.S Treasuries 35,318 — (378 ) 34,940 Government securities 57,646 — (310 ) 57,336 Corporate debt securities 120,752 — (1,205 ) 119,547 Total marketable securities $ 632,912 $ — $ (2,634 ) $ 630,278 Marketable securities at December 31, 2017 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 8,081 $ — $ (11 ) $ 8,070 U.S. Treasuries 113,852 — (119 ) 113,733 Government securities 44,421 — (57 ) 44,364 Corporate debt securities 155,222 — (177 ) 155,045 Non-current: Certificates of deposit 960 — (8 ) 952 U.S. Treasuries 36,165 — (311 ) 35,854 Government securities 23,992 — (182 ) 23,810 Corporate debt securities 83,722 — (524 ) 83,198 Total marketable securities $ 466,415 $ — $ (1,389 ) $ 465,026 At March 31, 2018 and December 31, 2017 , we held both current and non-current investments. Investments classified as current have maturities of less than one year . Investments classified as non-current are those that: (i) have a maturity of one to two years , and (ii) we do not intend to liquidate within the next twelve months , although these funds are available for use and therefore classified as available-for-sale. At March 31, 2018 and December 31, 2017 , we held 257 and 240 debt securities that were in an unrealized loss position for less than one year, respectively. The aggregate fair value of debt securities in an unrealized loss position at March 31, 2018 and December 31, 2017 was $572.7 million and $439.4 million , respectively. There were no individual securities that were in a significant unrealized loss position as of March 31, 2018 and December 31, 2017 . Given our intent and ability to hold such securities until recovery, and the lack of material of change in the credit risk of these investments, we do not consider these marketable securities to be other-than-temporarily impaired as of March 31, 2018 and December 31, 2017 .

Collaboration Agreements

Collaboration Agreements	3 Months Ended
	Mar. 31, 2018
Revenue Recognition and Deferred Revenue [Abstract]
Collaboration Agreements	Collaboration Agreements Celgene Corporation To date, our revenue has primarily been generated from our collaboration agreements with Celgene, or collectively, the Collaboration Agreements. Celgene is a related party through ownership of our common stock. In April 2010, we entered into a discovery and development collaboration and license agreement focused on cancer metabolism, or the 2010 Agreement. The 2010 Agreement was amended in October 2011 and July 2014. In April 2015, we entered into a joint worldwide development and profit share collaboration and license agreement with Celgene, and our wholly owned subsidiary, Agios International Sarl, entered into a collaboration and license agreement with Celgene International II Sarl, or collectively, the AG-881 Agreements, to establish a worldwide collaboration focused on the development and commercialization of AG-881 products. In May 2016, we entered into a master research and collaboration agreement with Celgene, or the 2016 Agreement. 2016 Agreement In May 2016, we entered into the 2016 Agreement focused on metabolic immuno-oncology, or MIO, a developing field which aims to modulate the activity of relevant immune cells by targeting critical metabolic nodes, thereby, enhancing the immune mediated anti-tumor response. In addition to new programs identified under the 2016 Agreement, both parties also agreed that all future development and commercialization of two remaining cancer metabolism programs discovered under the 2010 Agreement, including AG-270, an inhibitor of methionine adenosyltransferase 2a, will now be governed by the 2016 Agreement. During the research term of the 2016 Agreement, we plan to conduct research programs focused on discovering compounds that are active against metabolic targets in the immuno-oncology, or IO, field. The initial four-year research term will expire on May 17, 2020, and may be extended for up to two, or in specified cases, up to four additional one-year terms. For each program under the 2016 Agreement, we may nominate compounds that meet specified criteria as development candidates and, in limited circumstances, Celgene may also nominate compounds as development candidates for each such program. Celgene may designate the applicable program for further development following any such nomination, after which we may conduct, at our expense, additional preclinical and clinical development for such program through the completion of an initial phase 1 dose escalation study. At the end of the research term, Celgene may designate for continued development up to three research programs for which development candidates have yet to be nominated, which are referred to as continuation programs. We may conduct further research and preclinical and clinical development activities on any continuation program, at our expense, through the completion of an initial phase 1 dose escalation study. We granted Celgene the right to obtain exclusive options for development and commercialization rights for each program that Celgene has designated for further development, and for each continuation program. Celgene may exercise each such option beginning on the designation of a development candidate for such program (or on the designation of such program as a continuation program) and ending on the earlier of: (i) the end of a specified period after we have furnished Celgene with specified information about the initial phase 1 dose escalation study for such program, or (ii) January 1, 2030. Research programs that have applications in the inflammation or autoimmune, or I&I, field that may result from the 2016 Agreement will also be subject to the exclusive options described above. We will retain rights to any program that Celgene does not designate for further development or as to which it does not exercise its option. Under the terms of the 2016 Agreement, following Celgene’s exercise of its option with respect to a program, the parties will enter into either a co-development and co-commercialization agreement if such program is in the IO field, or a license agreement if such program is in the I&I field. Under each co-development and co-commercialization agreement, the two parties will co-develop and co-commercialize licensed products worldwide. Either we or Celgene will lead development and commercialization of licensed products for the United States, and Celgene will lead development and commercialization of licensed products outside of the United States. Depending on the country, the parties will each have the right to provide a portion of field-based marketing activities. Under each license agreement, Celgene will have the sole right to develop and commercialize licensed products worldwide. Co-development and co-commercialization agreements Under each co-development and co-commercialization agreement entered into under the 2016 Agreement, the parties will split all post-option exercise worldwide development costs, subject to specified exceptions, as well as any profits from any net sales of, or commercialization losses related to, licensed products in the IO field. Celgene has the option to designate one program in the IO field as the 65/35 program, for which Celgene will be the lead party for the United States and will have a 65% profit or loss share. For programs in the IO field other than the 65/35 program, we and Celgene will alternate, on a program-by-program basis, being the lead party for the United States, with us having the right to be the lead party for the first such program, and each party will have a 50% profit or loss share. The lead party for the United States will book commercial sales of licensed products, if any, in the United States, and Celgene will book commercial sales of licensed products, if any, outside of the United States. License agreements Under each license agreement under the 2016 Agreement, Celgene will be responsible for all post-option exercise worldwide development and associated costs, subject to specified exceptions, as well as worldwide commercialization and associated costs, for licensed products in the I&I field. Financial terms Under the terms of the 2016 Agreement, we received an initial upfront payment in the amount of $200.0 million . The 2016 Agreement provides specified rights to extend the research term for up to two , or in specified cases, up to four , additional years by paying a $40.0 million per-year extension fee. Celgene will pay an $8.0 million designation fee for each program that Celgene designates for further development and for each continuation program. During the three months ended March 31, 2017, we received $8.0 million from Celgene upon the designation of AG-270 as a development candidate. For each program as to which Celgene exercises its option to develop and commercialize, subject to antitrust clearance, Celgene will pay an option exercise fee of at least $30.0 million for any designated development program and at least $35.0 million for any continuation programs. In certain cases, Celgene may exercise its option to develop and commercialize two early-stage I&I programs, prior to Celgene designating the program for further development, by paying an option exercise fee of $10.0 million . We are eligible to receive the following milestone-based payments associated with the 2016 Agreement: Program Milestone Amount 65/35 program in IO field Specified clinical development event $25.0 million 65/35 program in IO field Specified regulatory milestone events Up to $183.8 million 50/50 program in IO field Specified clinical development event $20.0 million 50/50 program in IO field Specified regulatory milestone events Up to $148.8 million I&I field Specified clinical development event $25.0 million I&I field Specified regulatory milestone events Up to $236.3 million I&I field Specified commercial milestone events Up to $125.0 million Additionally, for each licensed program in the I&I field, we are eligible to receive royalties at tiered, low double-digit percentage rates on Celgene’s net sales, if any. Opt-out right Under the 2016 Agreement, we may elect to opt out of the cost and profit share under any co-development and co-commercialization agreement, subject to specified exceptions. Upon opting out, Celgene will have the sole right to develop, manufacture and commercialize the applicable licensed products throughout the world, at its cost, and we will undertake transitional activities reasonably necessary to transfer the development, manufacture and commercialization of such licensed products to Celgene, at our expense. Further, in lieu of the profit or loss sharing described above, we would be eligible to receive royalties at tiered, low double-digit percentage rates on Celgene’s net sales, if any, of the applicable licensed products. However, we would continue to be eligible to receive the developmental and regulatory milestone-based payments described above. Term The term of the 2016 Agreement commenced on May 17, 2016 and, if not terminated earlier, will expire upon the later of the last-to-expire of the research term and all option exercise periods, or, if an option is exercised by Celgene for one or more programs in the collaboration, upon the termination or expiration of the last-to-exist co-development and co-commercialization agreement or license agreement, as applicable, for any such program. Termination Subject to specified exceptions, Celgene may terminate the 2016 Agreement in its entirety for any reason by providing us with prior written notice if there are no active co-development and co-commercialization agreements or license agreements in place or on a program-by-program basis if there are no active co-development and co-commercialization agreements or license agreements in place for the terminated program(s). Either party may terminate the 2016 Agreement for the insolvency of the other party. On a program-by-program basis, prior to the exercise of an option, either party may terminate the 2016 Agreement either in its entirety or with respect to one or more programs on prior written notice to the other party in the case of an uncured material breach by the other party that frustrates the fundamental purpose of the 2016 Agreement. Following the exercise of an option for a program, either party may terminate the 2016 Agreement with respect to such program if such party terminates the co-development and co-commercialization agreement or license agreement for such program for an uncured material breach by the other party that frustrates the fundamental purpose of such agreement. Either party may terminate a co-development and co-commercialization agreement or a license agreement upon the bankruptcy or insolvency of the other party. Either party also has the right to terminate the co-development and co-commercialization agreement or license agreement if the other party or any of its affiliates challenges the validity, scope or enforceability of or otherwise opposes, any patent included within the intellectual property rights licensed to the other party under such agreement. Exclusivity While any of Celgene’s options remain available under the 2016 Agreement, subject to specified exceptions, we may not directly or indirectly develop, manufacture or commercialize, outside of the 2016 Agreement, any therapeutic modality in the IO or I&I field with specified activity against a metabolic target. During the term of each co-development and co-commercialization agreement and license agreement, subject to specified exceptions, neither we nor Celgene may directly or indirectly develop, manufacture or commercialize outside of such agreement any therapeutic modality in any field with specified activity against the metabolic target that is the focus of the program licensed under such agreement. TIBSOVO® (ivosidenib) Letter Agreement In May 2016, we entered into a letter agreement with Celgene regarding TIBSOVO® (ivosidenib), or the TIBSOVO® (ivosidenib) Letter Agreement. Under the TIBSOVO® (ivosidenib) Letter Agreement, the parties agreed to terminate the 2010 Agreement, effective as of August 15, 2016, as to the program directed to the isocitrate dehydrogenase 1, or IDH1, target, for which TIBSOVO® (ivosidenib) is the lead development candidate. Under the 2010 Agreement, Celgene had held development and commercialization rights to the IDH1 program outside of the United States, and we held such rights inside the United States. As a result of the termination, we obtained global rights to TIBSOVO® (ivosidenib) and the IDH1 program. Neither party will have any further financial obligation, including royalties or milestone payments, to the other concerning TIBSOVO® (ivosidenib) or the IDH1 program. Under the terms of the termination, the parties also agreed to conduct specified transitional activities in connection with the termination. In addition, pursuant to the TIBSOVO® (ivosidenib) Letter Agreement, the parties are released from their exclusivity obligations under the 2010 Agreement with respect to the IDH1 program. The termination does not affect the AG-881 Agreements , which are directed to both the IDH1 target and the isocitrate dehydrogenase 2, or IDH2, target. AG-881 Agreements In April 2015, we entered into the AG-881 Agreements. The AG-881 Agreements establish a joint worldwide collaboration focused on the development and commercialization of AG-881 products. Under the terms of the AG-881 Agreements, we received an initial upfront payment of $10.0 million in May 2015 and are eligible to receive milestone-based payments described below. The parties will split all worldwide development costs equally, subject to specified exceptions, as well as any profits from any net sales of, or commercialization losses related to, licensed AG-881 products. Either party may, at its own expense and with the other party's permission, undertake additional development activities outside of the scope of the development plan agreed upon with the other party. We are eligible to receive up to $70.0 million in potential milestone payments under the AG-881 Agreements. The potential milestone payments are comprised of: (i) a $15.0 million milestone payment for filing of a first new drug application, or NDA, in a major market, and (ii) up to $55.0 million in milestone payments upon achievement of specified regulatory milestone events. We may also receive royalties at tiered, low-double digit to mid-teen percentage rates on net sales if we elect not to participate in the development and commercialization of AG-881. Termination Celgene may terminate the AG-881 Agreements in their entirety for any reason upon ninety days written notice to us. Either party may terminate the AG-881 Agreements for the insolvency of the other party. Either party may terminate the AG-881 Agreements in their entirety or with respect to one of the agreements upon prior written notice to the other party in the case of an uncured material breach by the other party that frustrates the fundamental purpose of the AG-881 Agreements. If one of the AG-881 Agreements terminates, the other will terminate automatically. 2010 Agreement In April 2010, we entered into the 2010 Agreement, which was amended in October 2011 and July 2014. The goal of the collaboration was to discover, develop and commercialize disease-altering therapies in oncology based on our cancer metabolism research platform. We initially led discovery, preclinical and early clinical development for all cancer metabolism programs under the collaboration. The discovery phase of the 2010 Agreement expired in April 2016. Upon agreement to terminate the 2010 Agreement, effective as of August 15, 2016, as to the program directed to the IDH1 target, for which TIBSOVO® (ivosidenib) is the lead development candidate, the sole program remaining under the 2010 Agreement is IDHIFA®, a co-commercialized licensed program for which Celgene leads and funds global development and commercialization activities. We have exercised our right to participate in a portion of commercialization activities in the United States for IDHIFA® in accordance with the applicable commercialization plan. On August 1, 2017, the U.S. Food and Drug Administration, or FDA, granted Celgene approval of IDHIFA® for the treatment of adult patients with relapsed or refractory acute myeloid leukemia, or R/R AML, with an IDH2 mutation as detected by an FDA-approved test. Under the remaining terms of the 2010 Agreement, we are eligible to receive up to $95.0 million in potential milestone payments for the IDHIFA® program. The potential milestone payments are comprised of: (i) up to $70.0 million in milestone payments upon achievement of specified ex-U.S. regulatory milestone events, and (ii) a $25.0 million milestone payment upon achievement of a specified ex-U.S. commercial milestone event. Under the 2010 Agreement, we may also receive royalties at tiered, low-double digit to mid-teen percentage rates on net sales of IDHIFA®. Assuming all other revenue recognition criteria are met, royalty payments will be recognized as revenue in the period in which they are earned. During the three months ended March 31, 2018 , we earned $1.4 million in royalty revenue under the 2010 Agreement. Unless terminated earlier by either party, the term of the 2010 Agreement will continue until the expiration of all royalty terms with respect to IDHIFA®. Celgene may terminate this agreement for convenience in its entirety upon ninety days written notice to us. If either party is in material breach and fails to cure such breach within the specified cure period, the other party may terminate the 2010 Agreement in its entirety. Either party may terminate the agreement in the event of specified insolvency events involving the other party. Accounting analysis and revenue recognition – collaboration revenue On January 1, 2018 we adopted ASC 606 under the modified retrospective method. Prior to January 1, 2018 we accounted for the Collaboration Agreements under ASC 605-25, Multiple Element Arrangements. Accounting under ASC 606 In adopting ASC 606, we applied the practical expedient that permits aggregating the effect of all modifications that occurred prior to January 1, 2018. No other practical expedients were used. Similar to the accounting under ASC 605-25, the 2016 Agreement was determined to be a modification of the 2010 Agreement and the AG-881 Agreements. In determining the appropriate amount of revenue to be recognized under ASC 606, we performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) we satisfy each performance obligation. As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price, or SSP, for each performance obligation identified in the contract. We use key assumptions to determine the SSP, which include forecast of revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success. The satisfied and unsatisfied performance obligations at the time of the ASC 606 adoption, each of which are considered by us to be distinct within the context of the contract, their SSP, the method of recognizing the allocated consideration, and the period through which they are expected to be recognized are as follows: Performance Obligations SSP No. of Performance Obligation(s) Recognition Method Fully satisfied at time of adoption Licenses (1) $ 86.7 million 4 Fully satisfied; recognized upon adoption of ASC 606 Research and development services (2) (3) $ 350.7 million 10 Fully satisfied; recognized upon adoption of ASC 606 Partially satisfied at time of adoption Research and development services (2) (3) $ 266.6 million 6 Proportionally as services are delivered over the performance period, expected to be through September 2022 (4) (1) The SSP was developed by probability weighting multiple cash flow scenarios using the income approach. Our management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimate of the direct cost incurred to generate future cash flows, a discount rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the SSP of these units of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals, and other factors. If different reasonable assumptions are utilized, the SSP and revenue recognized would vary. (2) The SSP was developed using our management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider. (3) The SSP was developed using internal full time equivalent costs to support the development services. (4) We determined that recognizing revenue on a proportional basis using the ratio of effort incurred to date compared to the total estimated effort required to complete the performance obligation best depicts the satisfaction of our obligations under the Collaboration Agreements. During the three months ended March 31, 2018 , we recognized the following as collaboration revenue (in thousands): Three Months Ended March 31, 2018 Performance Obligation Under Topic Under Topic Effect of Collaboration revenue - related party Research and development services $ 6,364 $ 8,953 $ (2,589 ) Committee participations — 43 (43 ) Reduction of research and development expenses Development services — 411 (411 ) During the three months ended March 31, 2017 , we recognized as collaboration revenue the following non-contingent consideration allocated to each undelivered element (in thousands): Undelivered Element Revenue Recognized On-going research and development services $ 10,387 Committee participations 42 Total collaboration revenue - related party $ 10,429 During the three months ended March 31, 2017 , we recognized $2.8 million as a reduction of research and development expenses. During the three months ended March 31, 2018 , we did not recognize any reductions to research and development expenses. Development and commercialization expenses that were not contemplated as of the modification dates due to the high level of uncertainty are recognized as collaboration revenue or a reduction of research and development expenses in the period in which they are earned. There was no impact from the adoption of ASC 606 on these obligations. For the three months ended March 31, 2018 and 2017 , we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands): Three Months Ended March 31, 2018 2017 Collaboration revenue - related party Commercialization activities $ 981 $ 79 Reduction of research and development expenses Research and development activities — 14 For the three months ended March 31, 2018 and 2017 , we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands): Three Months Ended March 31, 2018 2017 Collaboration revenue - related party $ 7,345 $ 10,508 Reduction of research and development expenses — 2,776 The following table presents changes in our contract assets and liabilities during the three months ended March 31, 2018 (in thousands): December 31, 2017 Additions Deductions March 31, 2018 Contract assets (1) Collaboration receivable – related party $ 2,448 $ 3,512 $ (2,448 ) $ 3,512 Royalty receivable – related party 1,222 1,417 (1,222 ) 1,417 Contract liabilities (2) Deferred revenue – related party, current and net of current portions 163,640 4,204 (46,801 ) 121,043 (1) Additions to contract assets relate to amounts billed to Celgene for reimbursable costs incurred by us during the reporting period. Deductions to contract assets relate to collection of receivables during the reporting period. (2) Additions to contract liabilities relate to consideration from Celgene during the reporting period. Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period and cumulative catch-up adjustment recognized upon adoption of ASC 606 on January 1, 2018. During the three months ended March 31, 2018 , we recognized the following as revenue due to changes in the contract asset and the contract liability balances (in thousands): Amounts included in the contract liability at the beginning of the period $ 5,984 Performance obligations satisfied in previous periods 323 As of March 31, 2018 , the aggregate amount of the transaction price allocated to performance obligations that are partially unsatisfied was $132.6 million . We consider the total consideration expected to be earned in the next twelve months for services to be performed as current deferred revenue, and consideration that is expected to be earned subsequent to twelve months from the balance sheet date as noncurrent deferred revenue. Accounting analysis and revenue recognition – milestone revenue At each reporting period we evaluate whether milestones are considered probable of being reached and, to the extent that a significant reversal would not occur in future periods, estimate the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within our control, such as regulatory approvals, are not considered probable of being achieved and are excluded from the transaction price until those approvals are received. No milestones were earned during the three months ended March 31, 2018 and 2017 . The next potential milestone expected to be achieved under our collaboration agreements with Celgene is the filing of a first new drug application equivalent in an ex-U.S. country. Achievement of this event will result in milestone payments of $15.0 million under the 2010 Agreement. Aurigene Discovery Technologies Limited In April 2017, we entered into a new global license agreement with Aurigene Discovery Technologies Limited, or Aurigene, to research, develop and commercialize small molecule inhibitors for dihydroorotate dehydrogenase, or DHODH, or the Aurigene Agreement. Under the terms of the Aurigene Agreement, Aurigene will provide to us exclusive rights to its portfolio of novel small molecules for DHODH. Financial terms of the Aurigene Agreement include a $3.0 million upfront payment and potential future milestone payments of up to $17.0 million if we achieve certain development and regulatory milestones. The next potential milestone expected to be achieved under our collaboration agreements with Aurigene is the initiation of the first phase 1 clinical trial for AG-636, our DHODH inhibitor. Achievement of this event will result in milestone payments owed to Aurigene of $2.0 million . Aurigene is also eligible to receive low single-digit royalties on net product sales, if any. We will conduct preclinical studies and, if successful, fund further global research and development, as well as regulatory and commercial activities. The term of the Aurigene Agreement will continue until the earlier of: (a) termination for convenience at our sole discretion upon 90 days prior written notice, (b) termination by either party for material breach, or (c) the expiration of the last-to-expire of all payment obligations hereunder with respect to all licensed products under the Aurigene Agreement. Accounting analysis The $3.0 million upfront payment was incurred in May 2017 and recorded as research and development expense. Costs incurred and milestone payments due to Aurigene prior to regulatory approval are recognized as expenses in the period incurred. Payments due to Aurigene upon or subsequent to regulatory approval will be capitalized and amortized over the shorter of the remaining license or product patent life.

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses consist of the following (in thousands): March 31, December 31, Accrued compensation $ 4,966 $ 15,693 Accrued research and development costs 9,951 14,849 Accrued professional fees 1,853 3,140 Accrued other 235 349 Total accrued expenses $ 17,005 $ 34,031

Share-Based Payments

Share-Based Payments	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Payments	Share-Based Payments 2013 Stock Incentive Plan In June 2013, our Board of Directors adopted and, in July 2013 our stockholders approved, the 2013 Stock Incentive Plan, or the 2013 Plan. The 2013 Plan became effective upon the closing of our initial public offering and provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, or RSUs, performance-based stock units, or PSUs, and other stock-based awards. Following the adoption of the 2013 Plan, we granted no further stock options or other awards under the 2007 Stock Incentive Plan, or the 2007 Plan. Any options or awards outstanding under the 2007 Plan at the time of adoption of the 2013 Plan remained outstanding and effective. As of March 31, 2018 , the total number of shares reserved under the 2007 Plan and the 2013 Plan are 8,624,887 , and we had 1,938,247 shares available for future issuance under the 2013 Plan. Stock options The following table presents stock option activity for the three months ended March 31, 2018 : Number of Stock Options Weighted- Average Exercise Price Outstanding at December 31, 2017 5,577,562 $ 49.58 Granted 1,107,220 77.22 Exercised (477,847 ) 22.81 Forfeited/Expired (102,127 ) 88.78 Outstanding at March 31, 2018 6,104,808 $ 56.03 Exercisable at March 31, 2018 2,863,417 $ 48.14 Vested and expected to vest at March 31, 2018 6,104,808 $ 56.03 At March 31, 2018 , the total unrecognized compensation expense related to unvested stock option awards was $130.0 million , which we expect to recognize over a weighted-average period of approximately 3.0 years . Restricted stock units The following table presents RSU activity for the three months ended March 31, 2018 : Number of Stock Units Weighted-Average Grant Date Fair Value Unvested shares at December 31, 2017 125,584 $ 47.46 Granted 338,093 77.54 Vested (57,250 ) 41.76 Forfeited (781 ) 77.70 Unvested shares at March 31, 2018 405,646 $ 73.28 As of March 31, 2018 , there was approximately $26.7 million of total unrecognized compensation expense related to RSUs, which we expect to be recognized over a weighted-average period of approximately 2.6 years . Performance-based stock units The following table presents PSU activity for the three months ended March 31, 2018 : Number of Stock Units Weighted-Average Grant Date Fair Value Unvested shares at December 31, 2017 176,186 $ 52.98 Granted — — Vested — — Forfeited — — Unvested shares at March 31, 2018 176,186 $ 52.98 Stock-based compensation expense associated with these PSUs is recognized if the underlying performance condition is considered probable of achievement using our management’s best estimates. Performance-based vesting criteria primarily relate to milestone events specific to our corporate goals, specifically regulatory milestones related to our product candidates. As of March 31, 2018 , there was approximately $9.3 million of total unrecognized compensation expense related to PSUs with performance-based vesting criteria that are not considered probable of achievement. 2013 Employee Stock Purchase Plan In June 2013, our Board of Directors adopted, and in July 2013 our stockholders approved, the 2013 Employee Stock Purchase Plan, or the 2013 ESPP. We issued 27,377 shares and 33,521 shares during the three months ended March 31, 2018 and 2017 , respectively, under the 2013 ESPP. The 2013 ESPP provides participating employees with the opportunity to purchase up to an aggregate of 327,272 shares of our common stock. As of March 31, 2018 , we had 186,414 shares available for future issuance under the 2013 ESPP. Stock-based compensation expense Stock-based compensation expense by award type included within the condensed consolidated statements of operations is as follows (in thousands): Three Months Ended March 31, 2018 2017 Stock options $ 12,472 $ 9,902 Restricted stock units 1,797 595 Employee Stock Purchase Plan 253 237 Total stock-based compensation expense $ 14,522 $ 10,734 Expenses related to equity-based awards were allocated as follows in the condensed consolidated statements of operations (in thousands): Three Months Ended March 31, 2018 2017 Research and development expense $ 8,640 $ 7,025 General and administrative expense 5,882 3,709 Total stock-based compensation expense $ 14,522 $ 10,734

Loss per Share

Loss per Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Loss per Share	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 the 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 dilutive net loss per share calculation, stock options, RSUs and ESPP options are considered to be common stock equivalents, while PSUs with vesting conditions that were not met as of March 31, 2018 are not considered to be common stock equivalents. Since we had a net loss for all periods presented, the effect of all potentially dilutive securities is anti-dilutive. Accordingly, basic and diluted net loss per share was the same for all periods presented. The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2018 2017 Stock options 6,104,808 6,129,794 Restricted stock units 405,646 126,850 Employee Stock Purchase Plan options 5,289 5,533 Total common stock equivalents 6,515,743 6,262,177

Summary of Significant Accoun16

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The condensed consolidated balance sheet as of March 31, 2018 , and the condensed consolidated statements of operations, comprehensive loss, and cash flows for the three months ended March 31, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of our management, reflect all adjustments, which include only normal recurring adjustments, necessary to fairly state our financial position as of March 31, 2018 , and our results of operations and cash flows for the three months ended March 31, 2018 and 2017 . The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three -month period are also unaudited. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The year-end condensed consolidated balance sheet data was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. Accordingly, the condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2017 that was filed with the Securities and Exchange Commission, or the SEC, on February 14, 2018 . Our consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, Agios Securities Corporation, Agios International Sarl, and Agios Limited. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. GAAP.
Significant accounting policies and Recent accounting pronouncements	Significant accounting policies Revenue from Contracts with Customers In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) , or ASU 2014-09. ASU 2014-09 was codified as Accounting Standards Codification, or ASC, 606, Revenue from Contracts with Customers , or ASC 606. Subsequently, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606) , which adjusted the effective date of ASU 2014-09; ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net) , which amends the principal-versus-agent implementation guidance and illustrations in ASU 2014-09; ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, which clarifies identifying performance obligations and licensing implementation guidance and illustrations in ASU 2014-09; ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , which addresses implementation issues and is intended to reduce the cost and complexity of applying the new revenue standard in ASU 2014-09; ASU No. 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (SEC Update) , which codifies recent announcements by the SEC staff; and ASU No. 2017-14, Income Statement—Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606) (SEC Update) , which codifies SEC Release 33-10403, or collectively with ASU 2014-09, the Revenue ASUs. We were required to adopt the Revenue ASUs effective January 1, 2018. The guidance permits two methods of adoption: retrospectively to each prior reporting period presented (the full retrospective method), or retrospectively with the cumulative effect of initially applying the guidance recognized at the date of initial application (the modified retrospective method). We adopted the new standard under the modified retrospective method. In adopting the Revenue ASUs, we applied the practical expedient that permits aggregating the effect of all modifications that occurred prior to January 1, 2018. No other practical expedients were used. Upon finalization of our assessment, which resulted in changes to our estimates as of December 31, 2017, the impact of the cumulative effect of the accounting changes upon the adoption of the standard (in thousands) is as follows: December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue – related party, current and net of current portions $ 163,640 $ (39,456 ) $ 124,184 Accumulated deficit (798,061 ) 39,456 (758,605 ) The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements for the three months ended March 31, 2018 (in thousands, except per share data): Condensed Consolidated Balance Sheets March 31, 2018 Under Topic Under Topic Effect of Deferred revenue – related party $ 39,212 $ 35,396 $ 3,816 Deferred revenue, net of current portion – related party 81,831 122,060 (40,229 ) Accumulated deficit (849,430 ) (885,843 ) 36,413 Condensed Consolidated Statements of Operations Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Collaboration revenue – related party $ 7,345 $ 9,977 $ (2,632 ) Research and development expense 78,224 77,813 411 Total operating expenses 102,774 102,363 411 Loss from operations (94,012 ) (90,969 ) (3,043 ) Net loss (90,825 ) (87,782 ) (3,043 ) Net loss per share – basic and diluted (1.63 ) (1.58 ) (0.05 ) Condensed Consolidated Statements of Comprehensive Loss Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Comprehensive loss (92,079 ) (89,036 ) (3,043 ) Condensed Consolidated Statements of Cash Flows Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Adjustments to reconcile net loss to net cash used in operating activities: Deferred revenue – related party (3,141 ) (6,184 ) 3,043 Recent accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), or ASU 2016-02, which establishes principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing and uncertainty of cash flows arising from a lease. ASU 2016-02 was codified as ASC 842, Leases . Subsequently, the FASB issued ASU 2017-13, Revenue Recognition (Topic 605), Revenue from Contracts with Customers (Topic 606), Leases (Topic 840), and Leases (Topic 842): Amendments to SEC Paragraphs Pursuant to the Staff Announcement at the July 20, 2017 EITF Meeting and Rescission of Prior SEC Staff Announcements and Observer Comments (SEC Update) , which codifies recent announcements by the SEC staff; and ASU 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842 , which provides a transition practical expedient for existing or expired land easements, or collectively with ASU 2016-02, the Leases ASUs. We will adopt ASC 842 effective January 1, 2019. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption.
Fair Value Measurements	We record cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures , establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our own assumptions (unobservable inputs). The hierarchy consists of three levels: Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, directly or indirectly, for substantially the full term of the asset or liability. Level 3 – Unobservable inputs that reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.
Marketable Securities	Our marketable securities are classified as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities , and are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive loss in stockholders’ equity and a component of total comprehensive loss in the condensed consolidated statements of comprehensive loss , until realized. Realized gains and losses are included in investment income on a specific-identification basis. At March 31, 2018 and December 31, 2017 , we held both current and non-current investments. Investments classified as current have maturities of less than one year . Investments classified as non-current are those that: (i) have a maturity of one to two years , and (ii) we do not intend to liquidate within the next twelve months , although these funds are available for use and therefore classified as available-for-sale.
Collaboration Revenue	On January 1, 2018 we adopted ASC 606 under the modified retrospective method. Prior to January 1, 2018 we accounted for the Collaboration Agreements under ASC 605-25, Multiple Element Arrangements. Accounting under ASC 606 In adopting ASC 606, we applied the practical expedient that permits aggregating the effect of all modifications that occurred prior to January 1, 2018. No other practical expedients were used. Similar to the accounting under ASC 605-25, the 2016 Agreement was determined to be a modification of the 2010 Agreement and the AG-881 Agreements. In determining the appropriate amount of revenue to be recognized under ASC 606, we performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) we satisfy each performance obligation. As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price, or SSP, for each performance obligation identified in the contract. We use key assumptions to determine the SSP, which include forecast of revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.
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 the 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 dilutive net loss per share calculation, stock options, RSUs and ESPP options are considered to be common stock equivalents, while PSUs with vesting conditions that were not met as of March 31, 2018 are not considered to be common stock equivalents. Since we had a net loss for all periods presented, the effect of all potentially dilutive securities is anti-dilutive. Accordingly, basic and diluted net loss per share was the same for all periods presented.

Summary of Significant Accoun17

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of Impact of New Accounting Pronouncements	the impact of the cumulative effect of the accounting changes upon the adoption of the standard (in thousands) is as follows: December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue – related party, current and net of current portions $ 163,640 $ (39,456 ) $ 124,184 Accumulated deficit (798,061 ) 39,456 (758,605 ) The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements for the three months ended March 31, 2018 (in thousands, except per share data): Condensed Consolidated Balance Sheets March 31, 2018 Under Topic Under Topic Effect of Deferred revenue – related party $ 39,212 $ 35,396 $ 3,816 Deferred revenue, net of current portion – related party 81,831 122,060 (40,229 ) Accumulated deficit (849,430 ) (885,843 ) 36,413 Condensed Consolidated Statements of Operations Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Collaboration revenue – related party $ 7,345 $ 9,977 $ (2,632 ) Research and development expense 78,224 77,813 411 Total operating expenses 102,774 102,363 411 Loss from operations (94,012 ) (90,969 ) (3,043 ) Net loss (90,825 ) (87,782 ) (3,043 ) Net loss per share – basic and diluted (1.63 ) (1.58 ) (0.05 ) Condensed Consolidated Statements of Comprehensive Loss Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Comprehensive loss (92,079 ) (89,036 ) (3,043 ) Condensed Consolidated Statements of Cash Flows Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Adjustments to reconcile net loss to net cash used in operating activities: Deferred revenue – related party (3,141 ) (6,184 ) 3,043 During the three months ended March 31, 2018 , we recognized the following as collaboration revenue (in thousands): Three Months Ended March 31, 2018 Performance Obligation Under Topic Under Topic Effect of Collaboration revenue - related party Research and development services $ 6,364 $ 8,953 $ (2,589 ) Committee participations — 43 (43 ) Reduction of research and development expenses Development services — 411 (411 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis	The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of March 31, 2018 (in thousands): Level 1 Level 2 Level 3 Total Cash equivalents $ 262,897 $ 84,827 $ — $ 347,724 Marketable securities: Certificates of deposit — 5,226 — 5,226 U.S. Treasuries — 179,580 — 179,580 Government securities — 128,968 — 128,968 Corporate debt securities — 316,504 — 316,504 Total cash equivalents and marketable securities $ 262,897 $ 715,105 $ — $ 978,002

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable securities at March 31, 2018 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 4,760 $ — $ (8 ) $ 4,752 U.S Treasuries 144,849 — (209 ) 144,640 Government securities 71,773 — (141 ) 71,632 Corporate debt securities 197,334 — (377 ) 196,957 Non-current: Certificates of deposit 480 — (6 ) 474 U.S Treasuries 35,318 — (378 ) 34,940 Government securities 57,646 — (310 ) 57,336 Corporate debt securities 120,752 — (1,205 ) 119,547 Total marketable securities $ 632,912 $ — $ (2,634 ) $ 630,278 Marketable securities at December 31, 2017 consisted of the following (in thousands): Amortized Unrealized Unrealized Fair Current: Certificates of deposit $ 8,081 $ — $ (11 ) $ 8,070 U.S. Treasuries 113,852 — (119 ) 113,733 Government securities 44,421 — (57 ) 44,364 Corporate debt securities 155,222 — (177 ) 155,045 Non-current: Certificates of deposit 960 — (8 ) 952 U.S. Treasuries 36,165 — (311 ) 35,854 Government securities 23,992 — (182 ) 23,810 Corporate debt securities 83,722 — (524 ) 83,198 Total marketable securities $ 466,415 $ — $ (1,389 ) $ 465,026

Collaboration Agreements (Table

Collaboration Agreements (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue Recognition and Deferred Revenue [Abstract]
Schedule of Milestone-Based Payments Associated With 2016 Agreement	We are eligible to receive the following milestone-based payments associated with the 2016 Agreement: Program Milestone Amount 65/35 program in IO field Specified clinical development event $25.0 million 65/35 program in IO field Specified regulatory milestone events Up to $183.8 million 50/50 program in IO field Specified clinical development event $20.0 million 50/50 program in IO field Specified regulatory milestone events Up to $148.8 million I&I field Specified clinical development event $25.0 million I&I field Specified regulatory milestone events Up to $236.3 million I&I field Specified commercial milestone events Up to $125.0 million
Schedule of Satisfied and Unsatisfied Performance Obligations	The satisfied and unsatisfied performance obligations at the time of the ASC 606 adoption, each of which are considered by us to be distinct within the context of the contract, their SSP, the method of recognizing the allocated consideration, and the period through which they are expected to be recognized are as follows: Performance Obligations SSP No. of Performance Obligation(s) Recognition Method Fully satisfied at time of adoption Licenses (1) $ 86.7 million 4 Fully satisfied; recognized upon adoption of ASC 606 Research and development services (2) (3) $ 350.7 million 10 Fully satisfied; recognized upon adoption of ASC 606 Partially satisfied at time of adoption Research and development services (2) (3) $ 266.6 million 6 Proportionally as services are delivered over the performance period, expected to be through September 2022 (4) (1) The SSP was developed by probability weighting multiple cash flow scenarios using the income approach. Our management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimate of the direct cost incurred to generate future cash flows, a discount rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the SSP of these units of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals, and other factors. If different reasonable assumptions are utilized, the SSP and revenue recognized would vary. (2) The SSP was developed using our management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider. (3) The SSP was developed using internal full time equivalent costs to support the development services. (4) We determined that recognizing revenue on a proportional basis using the ratio of effort incurred to date compared to the total estimated effort required to complete the performance obligation best depicts the satisfaction of our obligations under the Collaboration Agreements.
Schedule of Impact of New Accounting Pronouncements	the impact of the cumulative effect of the accounting changes upon the adoption of the standard (in thousands) is as follows: December 31, 2017 Cumulative Effect January 1, 2018 Deferred revenue – related party, current and net of current portions $ 163,640 $ (39,456 ) $ 124,184 Accumulated deficit (798,061 ) 39,456 (758,605 ) The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements for the three months ended March 31, 2018 (in thousands, except per share data): Condensed Consolidated Balance Sheets March 31, 2018 Under Topic Under Topic Effect of Deferred revenue – related party $ 39,212 $ 35,396 $ 3,816 Deferred revenue, net of current portion – related party 81,831 122,060 (40,229 ) Accumulated deficit (849,430 ) (885,843 ) 36,413 Condensed Consolidated Statements of Operations Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Collaboration revenue – related party $ 7,345 $ 9,977 $ (2,632 ) Research and development expense 78,224 77,813 411 Total operating expenses 102,774 102,363 411 Loss from operations (94,012 ) (90,969 ) (3,043 ) Net loss (90,825 ) (87,782 ) (3,043 ) Net loss per share – basic and diluted (1.63 ) (1.58 ) (0.05 ) Condensed Consolidated Statements of Comprehensive Loss Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Comprehensive loss (92,079 ) (89,036 ) (3,043 ) Condensed Consolidated Statements of Cash Flows Three Months Ended March 31, 2018 Under Topic Under Topic Effect of Net loss $ (90,825 ) $ (87,782 ) $ (3,043 ) Adjustments to reconcile net loss to net cash used in operating activities: Deferred revenue – related party (3,141 ) (6,184 ) 3,043 During the three months ended March 31, 2018 , we recognized the following as collaboration revenue (in thousands): Three Months Ended March 31, 2018 Performance Obligation Under Topic Under Topic Effect of Collaboration revenue - related party Research and development services $ 6,364 $ 8,953 $ (2,589 ) Committee participations — 43 (43 ) Reduction of research and development expenses Development services — 411 (411 )
Summary of Multiple-deliverable Arrangements Revenue	For the three months ended March 31, 2018 and 2017 , we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands): Three Months Ended March 31, 2018 2017 Collaboration revenue - related party Commercialization activities $ 981 $ 79 Reduction of research and development expenses Research and development activities — 14 During the three months ended March 31, 2017 , we recognized as collaboration revenue the following non-contingent consideration allocated to each undelivered element (in thousands): Undelivered Element Revenue Recognized On-going research and development services $ 10,387 Committee participations 42 Total collaboration revenue - related party $ 10,429 For the three months ended March 31, 2018 and 2017 , we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands): Three Months Ended March 31, 2018 2017 Collaboration revenue - related party $ 7,345 $ 10,508 Reduction of research and development expenses — 2,776
Contract with Customer, Asset and Liability	During the three months ended March 31, 2018 , we recognized the following as revenue due to changes in the contract asset and the contract liability balances (in thousands): Amounts included in the contract liability at the beginning of the period $ 5,984 Performance obligations satisfied in previous periods 323 The following table presents changes in our contract assets and liabilities during the three months ended March 31, 2018 (in thousands): December 31, 2017 Additions Deductions March 31, 2018 Contract assets (1) Collaboration receivable – related party $ 2,448 $ 3,512 $ (2,448 ) $ 3,512 Royalty receivable – related party 1,222 1,417 (1,222 ) 1,417 Contract liabilities (2) Deferred revenue – related party, current and net of current portions 163,640 4,204 (46,801 ) 121,043 (1) Additions to contract assets relate to amounts billed to Celgene for reimbursable costs incurred by us during the reporting period. Deductions to contract assets relate to collection of receivables during the reporting period. (2) Additions to contract liabilities relate to consideration from Celgene during the reporting period. Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period and cumulative catch-up adjustment recognized upon adoption of ASC 606 on January 1, 2018.

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Summary of Accrued Expenses	Accrued expenses consist of the following (in thousands): March 31, December 31, Accrued compensation $ 4,966 $ 15,693 Accrued research and development costs 9,951 14,849 Accrued professional fees 1,853 3,140 Accrued other 235 349 Total accrued expenses $ 17,005 $ 34,031

Share-Based Payments (Tables)

Share-Based Payments (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Company's Stock Option Activity	The following table presents stock option activity for the three months ended March 31, 2018 : Number of Stock Options Weighted- Average Exercise Price Outstanding at December 31, 2017 5,577,562 $ 49.58 Granted 1,107,220 77.22 Exercised (477,847 ) 22.81 Forfeited/Expired (102,127 ) 88.78 Outstanding at March 31, 2018 6,104,808 $ 56.03 Exercisable at March 31, 2018 2,863,417 $ 48.14 Vested and expected to vest at March 31, 2018 6,104,808 $ 56.03
Unvested Stock Unit Activity	The following table presents RSU activity for the three months ended March 31, 2018 : Number of Stock Units Weighted-Average Grant Date Fair Value Unvested shares at December 31, 2017 125,584 $ 47.46 Granted 338,093 77.54 Vested (57,250 ) 41.76 Forfeited (781 ) 77.70 Unvested shares at March 31, 2018 405,646 $ 73.28
Schedule of Performance-Based Units	The following table presents PSU activity for the three months ended March 31, 2018 : Number of Stock Units Weighted-Average Grant Date Fair Value Unvested shares at December 31, 2017 176,186 $ 52.98 Granted — — Vested — — Forfeited — — Unvested shares at March 31, 2018 176,186 $ 52.98
Schedule of Stock-Based Compensation Expense by Award Type Included Within the Condensed Consolidated Statements of Operations	Stock-based compensation expense by award type included within the condensed consolidated statements of operations is as follows (in thousands): Three Months Ended March 31, 2018 2017 Stock options $ 12,472 $ 9,902 Restricted stock units 1,797 595 Employee Stock Purchase Plan 253 237 Total stock-based compensation expense $ 14,522 $ 10,734
Summary of Allocated Stock-Based Compensation Expense	Expenses related to equity-based awards were allocated as follows in the condensed consolidated statements of operations (in thousands): Three Months Ended March 31, 2018 2017 Research and development expense $ 8,640 $ 7,025 General and administrative expense 5,882 3,709 Total stock-based compensation expense $ 14,522 $ 10,734

Loss per Share (Tables)

Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Common Stock Excluded from Calculation of Diluted Earnings Per Share	The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2018 2017 Stock options 6,104,808 6,129,794 Restricted stock units 405,646 126,850 Employee Stock Purchase Plan options 5,289 5,533 Total common stock equivalents 6,515,743 6,262,177

Overview and Basis of Present24

Overview and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	8,152,986
Proceeds from public offering of common stock, net of commissions	$ 516,200	$ 516,206	$ 0
Cash, cash equivalents, and short-term investments		$ 994,700
Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	7,089,553
Offer price (in usd per share)	$ 67
Proceeds from public offering of common stock, net of commissions	$ 448,900
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	1,063,433
Proceeds from public offering of common stock, net of commissions	$ 67,300

Summary of Significant Accoun25

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Impact of the Cumulative Effect of Accounting Changes Upon Adoption of ASC 606 (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions		$ 124,184
Accumulated deficit	$ (849,430)	(758,605)	$ (798,061)
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions			163,640
Accumulated deficit	(885,843)		$ (798,061)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions		(39,456)
Accumulated deficit	$ 36,413	$ 39,456

Summary of Significant Accoun26

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party	$ 39,212		$ 37,842
Deferred revenue, net of current portion – related party	81,831		125,798
Accumulated deficit	(849,430)	$ (758,605)	(798,061)
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party	35,396
Deferred revenue, net of current portion – related party	122,060
Accumulated deficit	(885,843)		$ (798,061)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party	3,816
Deferred revenue, net of current portion – related party	(40,229)
Accumulated deficit	$ 36,413	$ 39,456

Summary of Significant Accoun27

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ 7,345	$ 10,508
Research and development expense	78,224	62,732
Total operating expenses	102,774	77,555
Loss from operations	(94,012)	(67,047)
Net loss	$ (90,825)	$ (66,166)
Net loss per share – basic and diluted (usd per share)	$ (1.63)	$ (1.56)
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ 9,977
Research and development expense	77,813
Total operating expenses	102,363
Loss from operations	(90,969)
Net loss	$ (87,782)
Net loss per share – basic and diluted (usd per share)	$ (1.58)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ (2,632)
Research and development expense	411
Total operating expenses	411
Loss from operations	(3,043)
Net loss	$ (3,043)
Net loss per share – basic and diluted (usd per share)	$ (0.05)

Summary of Significant Accoun28

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (90,825)	$ (66,166)
Comprehensive loss	(92,079)	$ (66,065)
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(87,782)
Comprehensive loss	(89,036)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(3,043)
Comprehensive loss	$ (3,043)

Summary of Significant Accoun29

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (90,825)	$ (66,166)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue – related party	(3,141)	$ (1,924)
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(87,782)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue – related party	(6,184)
Accounting Standards Update 2014-09 | ASC 606 Adjustments
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(3,043)
Adjustments to reconcile net loss to net cash used in operating activities:
Deferred revenue – related party	$ 3,043

Fair Value Measurements - Cash

Fair Value Measurements - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring $ in Thousands	Mar. 31, 2018USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 347,724
Total cash equivalents and marketable securities	978,002
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	5,226
U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	179,580
Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	128,968
Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	316,504
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	262,897
Total cash equivalents and marketable securities	262,897
Level 1 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 | U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 | Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	84,827
Total cash equivalents and marketable securities	715,105
Level 2 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	5,226
Level 2 | U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	179,580
Level 2 | Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	128,968
Level 2 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	316,504
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Total cash equivalents and marketable securities	0
Level 3 | Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 | U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 | Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 | Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	$ 0

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	Mar. 31, 2018USD ($)
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets (liabilities)	$ 0

Marketable Securities - Additio

Marketable Securities - Additional Information (Details)	3 Months Ended
	Mar. 31, 2018USD ($)security	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)security
Schedule of Available-for-sale Securities [Line Items]
Realized gain (loss) on marketable securities	$ 0	$ 0
Reclassifications out of accumulated other comprehensive income	$ 0	$ 0
Established time period for liquidation	12 months
Debt securities in an unrealized loss position | security	257		240
Aggregate fair value of debt securities in an unrealized loss position	$ 572,700,000		$ 439,400,000
Maximum
Schedule of Available-for-sale Securities [Line Items]
Minimum maturity (in years)	1 year
Maximum maturity (in years)	2 years
Minimum
Schedule of Available-for-sale Securities [Line Items]
Minimum maturity (in years)	1 year

Marketable Securities - Summary

Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 632,912	$ 466,415
Unrealized Gains	0	0
Unrealized Losses	(2,634)	(1,389)
Fair Value	630,278	465,026
Current: | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,760	8,081
Unrealized Gains	0	0
Unrealized Losses	(8)	(11)
Fair Value	4,752	8,070
Current: | U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	144,849	113,852
Unrealized Gains	0	0
Unrealized Losses	(209)	(119)
Fair Value	144,640	113,733
Current: | Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	71,773	44,421
Unrealized Gains	0	0
Unrealized Losses	(141)	(57)
Fair Value	71,632	44,364
Current: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	197,334	155,222
Unrealized Gains	0	0
Unrealized Losses	(377)	(177)
Fair Value	196,957	155,045
Non-current: | Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	480	960
Unrealized Gains	0	0
Unrealized Losses	(6)	(8)
Fair Value	474	952
Non-current: | U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	35,318	36,165
Unrealized Gains	0	0
Unrealized Losses	(378)	(311)
Fair Value	34,940	35,854
Non-current: | Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	57,646	23,992
Unrealized Gains	0	0
Unrealized Losses	(310)	(182)
Fair Value	57,336	23,810
Non-current: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	120,752	83,722
Unrealized Gains	0	0
Unrealized Losses	(1,205)	(524)
Fair Value	$ 119,547	$ 83,198

Collaboration Agreements - 2016

Collaboration Agreements - 2016 Agreement (Details) - 2016 Agreement	1 Months Ended
	May 31, 2016extensionprogram
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of research programs that can be designated for continued development after the research term | program	3
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Remaining cancer metabolism programs | program	2
Term of agreements	4 years
Extension period | extension	2
Number of allowable special case extensions | extension	4
Special case extension term	1 year

Collaboration Agreements - Co-D

Collaboration Agreements - Co-Development and Co-Commercialization Agreements (Details) - Co-Development and Co-Commercialization Agreements - Celgene	1 Months Ended
	May 31, 2016
65/35 Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	65.00%
Other Than 65/35 Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	50.00%

Collaboration Agreements - Fina

Collaboration Agreements - Financial Terms (Details) - Celgene - 2016 Agreement	May 17, 2016USD ($)	May 31, 2016USD ($)extension	Mar. 31, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 8,000,000	$ 200,000,000	$ 8,000,000
Extension period | extension		2
Number of allowable special case extensions | extension		4
Upfront payment agreement extension fee receivable		$ 40,000,000
Option exercise fee receivable	30,000,000
Additional option exercise fee for further development	10,000,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum option exercise fee receivable for continuation program	$ 35,000,000

Collaboration Agreements - Summ

Collaboration Agreements - Summary of Milestone-based Receivable Payments (Details) - Celgene $ in Millions	May 31, 2016USD ($)
Specified clinical development event | Co Commercial Agreement
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	$ 25
Specified clinical development event | 65/35 Program | Co-Development and Co-Commercialization Agreements
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	25
Specified clinical development event | Other Than 65/35 Program | Co-Development and Co-Commercialization Agreements
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	20
Specified regulatory milestone events | Maximum | Co Commercial Agreement
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	236.3
Specified regulatory milestone events | Maximum | 65/35 Program | Co-Development and Co-Commercialization Agreements
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	183.8
Specified regulatory milestone events | Maximum | Other Than 65/35 Program | Co-Development and Co-Commercialization Agreements
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	148.8
Specified commercial milestone events | Maximum | Co Commercial Agreement
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	$ 125

Collaboration Agreements - AG-8

Collaboration Agreements - AG-881 Agreements (Details) - AG-881 program licenses - USD ($)	1 Months Ended
	May 31, 2015	Mar. 31, 2018	Apr. 27, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 10,000,000
Milestone-based receivable payments, eligible to be received			$ 70,000,000
Milestone payment for filing of first NDA		$ 15,000,000	15,000,000
Milestone payments upon achievement of specified regulatory milestone events			$ 55,000,000

Collaboration Agreements - 2010

Collaboration Agreements - 2010 Agreement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty revenue	$ 1,417	$ 0
2010 Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone-based receivable payments, eligible to be received	95,000
Milestone payments upon achievement of specified regulatory milestone events	70,000
Milestone payment upon achievement of a specified commercial milestone event	$ 25,000

Collaboration Agreements - Sche

Collaboration Agreements - Schedule of Satisfied and Unsatisfied Performance Obligations (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)performance_obligation
Licenses | Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price | $	$ 86.7
No. of Performance Obligation(s) | performance_obligation	4
Research services | Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price | $	$ 350.7
No. of Performance Obligation(s) | performance_obligation	10
Research services | Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price | $	$ 266.6
No. of Performance Obligation(s) | performance_obligation	6

Collaboration Agreements - Sc41

Collaboration Agreements - Schedule of Effect of Adopting ASC 606 by Performance Obligation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ 7,345	$ 10,508
Reduction of research and development expenses	0	2,776
Before ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	9,977
ASC 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	(2,632)
Research services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	6,364
Research services | Before ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	8,953
Research services | ASC 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	(2,589)
Development services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	0	$ 2,800
Development services | Before ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	411
Development services | ASC 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	(411)
Committee participations
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	0
Committee participations | Before ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	43
Committee participations | ASC 606 Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ (43)

Collaboration Agreements - Su42

Collaboration Agreements - Summary of Collaboration Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 8,762	$ 10,508
Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party		10,429
Collaborative arrangement, product | Development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party		10,387
Collaborative arrangement, product | Committee participations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party		$ 42

Collaboration Agreements - Rema

Collaboration Agreements - Remaining Unsatisfied Performance Obligations (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining performance obligation, expected timing of satisfaction	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: (nil)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Remaining unsatisfied performance obligation	$ 132.6

Collaboration Agreements - Su44

Collaboration Agreements - Summary of Revenue Recognized as a Reduction of Research and Development Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction of research and development expenses	$ 0	$ 2,776
Development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction of research and development expenses	$ 0	$ 2,800

Collaboration Agreements - Deve

Collaboration Agreements - Development and Commercialization Expense Not Contemplated As Part Of Modifications (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 7,345	$ 10,508
Reduction of research and development expenses	0	2,776
Collaborative arrangement, product | Not Included In Modification Due To High Level Of Uncertainty | Commercialization activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	981	79
Collaborative arrangement, product | Not Included In Modification Due To High Level Of Uncertainty | Research and development activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction of research and development expenses	$ 0	$ 14

Collaboration Agreements - Coll

Collaboration Agreements - Collaboration Revenue and Research and Development Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue Recognition and Deferred Revenue [Abstract]
Collaboration revenue - related party	$ 7,345	$ 10,508
Reduction of research and development expenses	$ 0	$ 2,776

Collaboration Agreements - Sc47

Collaboration Agreements - Schedule of Changes in Contract Assets and Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Contract liabilities
Additions	$ 5,984
Collaboration receivable – related party
Contract assets
Contract assets, beginning balance	2,448
Additions	3,512
Deductions	(2,448)
Contract assets, ending balance	3,512
Royalty receivable – related party
Contract assets
Contract assets, beginning balance	1,222
Additions	1,417
Deductions	(1,222)
Contract assets, ending balance	1,417
Deferred revenue – related party, current and net of current portions
Contract liabilities
Contract liabilities, beginning balance	163,640
Additions	4,204
Deductions	(46,801)
Contract liabilities, ending balance	$ 121,043

Collaboration Agreements - Sc48

Collaboration Agreements - Schedule of Revenues as a Result of Changes in Contract Asset and Contract Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Revenue Recognition and Deferred Revenue [Abstract]
Amounts included in the contract liability at the beginning of the period	$ 5,984
Performance obligations satisfied in previous periods	$ 323

Collaboration Agreements - Acco

Collaboration Agreements - Accounting Analysis And Revenue Recognition - Milestone (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Apr. 27, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones achieved	$ 0	$ 0
AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment for filing of first NDA	$ 15,000,000		$ 15,000,000

Collaboration Agreements - Auri

Collaboration Agreements - Aurigene Discovery Technologies Limited (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	May 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 78,224	$ 62,732
Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 3,000
Potential future milestone payments				$ 17,000
DHODH Phase One Clinical Trial | Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone payments		$ 2,000

Accrued Expenses - Summary of A

Accrued Expenses - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued compensation	$ 4,966	$ 15,693
Accrued research and development costs	9,951	14,849
Accrued professional fees	1,853	3,140
Accrued other	235	349
Total accrued expenses	$ 17,005	$ 34,031

Share-Based Payments - Addition

Share-Based Payments - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 26.7
Weighted-average period to recognize compensation expense (in years)	2 years 6 months 26 days
2007 Plan and 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	8,624,887
Shares available for future issuance (in shares)	1,938,247
2013 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 130
Weighted-average period to recognize compensation expense (in years)	2 years 11 months 16 days
2013 Stock Incentive Plan | Performance-Based Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 9.3
2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)	186,414
Shares issued under 2013 ESPP (in shares)	27,377	33,521
Opportunity to purchase of common stock (in shares)	327,272

Share-Based Payments - Summary

Share-Based Payments - Summary of Company's Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Stock Options, Outstanding, Beginning balance (in shares) | shares	5,577,562
Number of Stock Options, Granted (in shares) | shares	1,107,220
Number of Stock Options, Exercised (in shares) | shares	(477,847)
Number of Stock Options, Forfeited/Expired (in shares) | shares	(102,127)
Number of Stock Options, Outstanding, Ending balance (in shares) | shares	6,104,808
Number of Stock Options, Exercisable (in shares) | shares	2,863,417
Number of Stock Options, Vested and expected to vest (in shares) | shares	6,104,808
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, Beginning balance (in usd per share) | $ / shares	$ 49.58
Weighted-Average Exercise Price, Granted (in usd per share) | $ / shares	77.22
Weighted-Average Exercise Price, Exercised (in usd per share) | $ / shares	22.81
Weighted-Average Exercise Price, Forfeited/Expired (in usd per share) | $ / shares	88.78
Weighted-Average Exercise Price, Outstanding, Ending balance (in usd per share) | $ / shares	56.03
Weighted-Average Exercise Price, Exercisable (in usd per share) | $ / shares	48.14
Weighted-Average Exercise Price, Vested and expected to vest (in usd per share) | $ / shares	$ 56.03

Share-Based Payments - Summar54

Share-Based Payments - Summary of Unvested RSUs Activity (Details) - Restricted stock units	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares beginning of period (in shares) | shares	125,584
Granted (in shares) | shares	338,093
Vested (in shares) | shares	(57,250)
Forfeited/expired (in shares) | shares	(781)
Unvested shares end of period (in shares) | shares	405,646
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, Unvested shares beginning of period (in usd per share) | $ / shares	$ 47.46
Weighted-average grant date fair value, Granted (in usd per share) | $ / shares	77.54
Weighted-average grant date fair value, Vested (in usd per share) | $ / shares	41.76
Weighted-average grant date fair value, Forfeited/expired (in usd per share) | $ / shares	77.70
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) | $ / shares	$ 73.28

Share-Based Payments - Schedule

Share-Based Payments - Schedule of Performance-Based Units (Details) - Performance-Based Stock Units (PSUs)	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares beginning of period (in shares) | shares	176,186
Granted (in shares) | shares	0
Vested (in shares) | shares	0
Forfeited/expired (in shares) | shares	0
Unvested shares end of period (in shares) | shares	176,186
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, Unvested shares beginning of period (in usd per share) | $ / shares	$ 52.98
Weighted-average grant date fair value, Granted (in usd per share) | $ / shares	0
Weighted-average grant date fair value, Vested (in usd per share) | $ / shares	0
Weighted-average grant date fair value, Forfeited/expired (in usd per share) | $ / shares	0
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) | $ / shares	$ 52.98

Share-Based Payments - Schedu56

Share-Based Payments - Schedule of Stock-Based Compensation Expense by Award Type Included Within the Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 14,522	$ 10,734
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	12,472	9,902
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1,797	595
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 253	$ 237

Share-Based Payments - Stock-Ba

Share-Based Payments - Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units, Performance-Based Stock Options, Performance-Based Stock Units and Employee Stock Purchase Plan Shares (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 14,522	$ 10,734
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	8,640	7,025
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 5,882	$ 3,709

Loss per Share - Common Stock E

Loss per Share - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,515,743	6,262,177
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,104,808	6,129,794
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	405,646	126,850
Employee Stock Purchase Plan options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,289	5,533