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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	AGIOS PHARMACEUTICALS INC
Trading Symbol (Optional DEI Element)	AGIO
Entity Central Index Key	0001439222
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		48,754,289

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 132,741	$ 160,754
Marketable securities	375,187	380,560
Collaboration receivable – related party	3,489	4,886
Royalty receivable – related party	715	0
Tenant improvement and other receivables	859	3,428
Prepaid expenses and other current assets	15,316	10,264
Total current assets	528,307	559,892
Marketable securities	133,804	32,250
Property and equipment, net	24,019	25,337
Other non-current assets	1,070	1,615
Total assets	687,200	619,094
Current liabilities:
Accounts payable	17,899	17,106
Accrued expenses	30,760	32,002
Deferred revenue – related party	35,867	35,913
Deferred rent	3,586	3,412
Total current liabilities	88,112	88,433
Deferred revenue, net of current portion – related party	134,202	154,297
Deferred rent, net of current portion	15,080	17,773
Total liabilities	237,394	260,503
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized; no shares issued or outstanding at September 30, 2017 and December 31, 2016	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized; 48,617,989 and 42,220,444 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	49	42
Additional paid-in capital	1,160,048	842,013
Accumulated other comprehensive loss	(515)	(313)
Accumulated deficit	(709,776)	(483,151)
Total stockholders’ equity	449,806	358,591
Total liabilities and stockholders’ equity	$ 687,200	$ 619,094

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
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)	48,617,989	42,220,444
Common stock, shares outstanding (in shares)	48,617,989	42,220,444

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Collaboration revenue – related party	$ 10,643	$ 8,985	$ 32,497	$ 47,244
Royalty revenue – related party	715	0	715	0
Total revenue	11,358	8,985	33,212	47,244
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)	72,917	60,643	215,465	155,485
General and administrative	17,458	11,854	48,411	35,335
Total operating expenses	90,375	72,497	263,876	190,820
Loss from operations	(79,017)	(63,512)	(230,664)	(143,576)
Interest income	1,880	678	4,279	1,591
Net loss	$ (77,137)	$ (62,834)	$ (226,385)	$ (141,985)
Net (loss) income per share – basic and diluted (usd per share)	$ (1.59)	$ (1.63)	$ (4.94)	$ (3.72)
Weighted-average number of common shares used in computing net (loss) income per share – basic and diluted (in shares)	48,459,424	38,548,153	45,851,203	38,124,425

Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Reduction of research and development expenses	$ 1,078	$ 4,038	$ 6,343	$ 18,754

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (77,137)	$ (62,834)	$ (226,385)	$ (141,985)
Other comprehensive income (loss)
Unrealized gain (loss) on available-for-sale securities	135	(268)	(202)	347
Comprehensive loss	$ (77,002)	$ (63,102)	$ (226,587)	$ (141,638)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net loss	$ (226,385)	$ (141,985)
Adjustments to reconcile net loss cash (used in) provided by operating activities:
Depreciation	4,778	3,986
Stock-based compensation expense	35,128	32,246
Net amortization of premium and discounts on investments	25	534
Loss on disposal of property and equipment	40	0
Changes in operating assets and liabilities:
Collaboration receivable – related party	1,397	43
Royalty receivable – related party	(715)	0
Tenant improvement and other receivables	2,558	271
Prepaid expenses and other current and non-current assets	(4,444)	(2,464)
Accounts payable	742	1,668
Accrued expenses	(1,242)	7,328
Deferred revenue – related party	(20,141)	185,992
Deferred rent	(2,519)	2,166
Net cash (used in) provided by operating activities	(210,778)	89,785
Investing activities
Purchases of marketable securities	(604,525)	(367,587)
Proceeds from maturities and sales of marketable securities	508,116	334,448
Purchases of property and equipment	(3,347)	(8,693)
Net cash used in investing activities	(99,756)	(41,832)
Financing activities
Payment of public offering costs, net of reimbursements	(89)	(124)
Proceeds from public offering of common stock, net of commissions	270,250	162,150
Net proceeds from stock option exercises and employee stock purchase plan	12,360	3,759
Net cash provided by financing activities	282,521	165,785
Net change in cash and cash equivalents	(28,013)	213,738
Cash and cash equivalents at beginning of the period	160,754	71,764
Cash and cash equivalents at end of the period	132,741	285,502
Supplemental disclosure of non-cash investing and financing transactions
Additions to property and equipment in accounts payable and accrued expenses	226	497
Proceeds from stock option exercises in other receivables	95	0
Public offering costs in other receivables, net of amounts in accounts payable and accrued expenses	$ 318	$ 124

Overview and Basis of Presentation	9 Months Ended
Overview and Basis of Presentation	Sep. 30, 2017
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 areas of focus are cancer metabolism, 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, and metabolic immuno-oncology, or MIO, which is a developing field that aims to modulate the activity of relevant immune cells (or tumor microenvironment) by targeting critical metabolic nodes, thereby enhancing the immune mediated anti-tumor response. In each of these areas, 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 September 30, 2017, and the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2017 and 2016, and cash flows for the nine months ended September 30, 2017 and 2016, 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 September 30, 2017, and our results of operations for the three and nine months ended September 30, 2017 and 2016, and cash flows for the nine months ended September 30, 2017 and 2016. The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three and nine-month period are also unaudited. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 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, 2016 that was filed with the Securities and Exchange Commission, or the SEC, on February 16, 2017. Our consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, Agios Securities Corporation and Agios International Sarl. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. GAAP. Liquidity In April 2017, we completed a public offering of 5,050,505 shares of common stock at an offering price of $49.50 per share. We received net proceeds from this offering of $235.0 million, after deducting underwriting discounts and commissions paid by us. In addition, we granted the underwriters the right to purchase up to an additional 757,575 shares of common stock, which was also exercised in April 2017, resulting in additional net proceeds to us of $35.2 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 5,808,080 shares, and net proceeds to us totaled $270.2 million, after underwriting discounts and commissions.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies and Recent Accounting Pronouncements	Summary of Significant Accounting Policies and Recent Accounting Pronouncements Significant accounting policies In the quarter ended March 31, 2017, we adopted Accounting Standards Update, or ASU, 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, or ASU 2016-09, which simplifies several aspects of the accounting for employee share-based payment transactions. There have been no other material changes to the significant accounting policies previously disclosed in our Annual Report on Form 10-K for the year ended December 31, 2016. Recent accounting pronouncements 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. 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; and 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, or collectively, the Revenue ASUs. The Revenue ASUs provide an accounting standard for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2017, with an option to early adopt for interim and annual periods beginning after December 15, 2016. 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 will adopt the new standard effective January 1, 2018 under the modified retrospective method. We have allocated internal resources to the implementation and are in the process of determining the impact of the Revenue ASUs on our financial statements; however, the adoption of the Revenue ASUs may have a material impact on revenue recognition, our notes to consolidated financial statements and our internal controls over financial reporting. As discussed further in detail within Note 5, Collaboration Agreements, our collaboration agreements with Celgene Corporation, or Celgene, are currently our sole source of revenue and the only arrangements impacted by the adoption of the Revenue ASUs. Other Recent Accounting Pronouncements In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, or ASU 2017-09, which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in the Accounting Standards Codification, or ASC, 718. ASU 2017-09 is effective for us for annual periods beginning after December 15, 2017, and interim periods therein, with early adoption permitted. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory, or ASU 2016-16, which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for us for annual periods beginning after December 15, 2017, and interim periods therein, with early adoption permitted. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. 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 is effective for us for annual periods beginning after December 15, 2018 and interim periods therein, with early adoption permitted. 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

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

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 the cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2017 (in thousands):



	Level 1		Level 2		Level 3		Total
Cash equivalents	$	88,556	$	19,993	$	—	$	108,549
Marketable securities:
Certificates of deposit	—		11,185		—		11,185
U.S. Treasuries	151,814		—		—		151,814
Government securities	53,131		13,701		—		66,832
Corporate debt securities	—		279,160		—		279,160
Total cash equivalents and marketable securities	$	293,501	$	324,039	$	—	$	617,540

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 September 30, 2017.

There have been no changes to the valuation methods during the nine months ended September 30, 2017. We evaluate transfers between levels at the end of each reporting period. Due to the lack of an active market, there were $4.0 million in transfers from Level 1 to Level 2 during the nine months ended September 30, 2017; due to the existence of an active market, there were $10.0 million in transfers of assets from Level 2 to Level 1 during the nine months ended September 30, 2017. There were no transfers of financial liabilities between Level 1 and Level 2 during the nine months ended September 30, 2017. We have no financial assets or liabilities that were classified as Level 3 at any point during the nine months ended September 30, 2017.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities at September 30, 2017 and December 31, 2016 consisted of investments in certificates of deposit, U.S. Treasuries, government securities and corporate debt securities. We determine the appropriate classification of the securities at the time they are acquired and evaluate the appropriateness of such classifications at each balance sheet date. We classify our marketable securities as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities. Marketable securities 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 and nine months ended September 30, 2017 and 2016 and, as a result, there were no reclassifications of any amounts out of accumulated other comprehensive loss for those periods.

Marketable securities at September 30, 2017 consist of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	10,240	$	1	$	(10	)	$	10,231
U.S Treasuries	113,824		4		(45		)	113,783
Government securities	42,443		—		(32		)	42,411
Corporate debt securities	208,850		3		(91		)	208,762
Non-current:
Certificates of deposit	960		—		(6		)	954
U.S Treasuries	38,162		—		(131		)	38,031
Government securities	24,492		—		(71		)	24,421
Corporate debt securities	70,535		2		(139		)	70,398
	$	509,506	$	10	$	(525	)	$	508,991

Marketable securities at December 31, 2016 consist of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	11,280	$	2	$	(3	)	$	11,279
U.S. Treasuries	141,678		2		(62		)	141,618
Government securities	19,533		—		(23		)	19,510
Corporate debt securities	208,285		3		(135		)	208,153
Non-current:
Certificates of deposit	7,600		6		(13		)	7,593
Government securities	4,499		—		(21		)	4,478
Corporate debt securities	20,248		—		(69		)	20,179
	$	413,123	$	13	$	(326	)	$	412,810

At September 30, 2017 and December 31, 2016, 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.

We review marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the condensed consolidated statements of operations if we experience a credit loss, have the intent to sell the marketable security, or if it is more likely than not that we will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with our investment policy, the severity and the duration of the impairment, and changes in value subsequent to the end of the period.

At September 30, 2017 and December 31, 2016, we held 238 and 158 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 September 30, 2017 and December 31, 2016 was $435.5 million and $335.4 million, respectively. There were no individual securities that were in a significant unrealized loss position as of September 30, 2017 and December 31, 2016. We evaluated our securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions. It is not more likely than not that we will be required to sell the securities, and we do not intend to do so prior to the recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of September 30, 2017 and December 31, 2016.

Collaboration Agreements

9 Months Ended

Sep. 30, 2017

Revenue Recognition and Deferred Revenue [Abstract]

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 collaboration agreement focused on cancer metabolism. The agreement was amended in October 2011 and July 2014, or collectively the agreement together with the amendments, the 2010 Agreement. On April 27, 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. On May 17, 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 MIO. 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, a program focused on methylthioadenosine phosphorylase, or MTAP, deleted cancers, 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.

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, our program focused on MTAP-deleted cancers, 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 their 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.

AG-120 Letter Agreement

On May 17, 2016, we entered into a letter agreement with Celgene regarding ivosidenib, or the AG-120 Letter Agreement. Under the AG-120 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 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 ivosidenib and the IDH1 program. Neither party will have any further financial obligation, including royalties or milestone payments, to the other concerning 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 AG-120 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

On April 27, 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 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 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 and nine months ended September 30, 2017, we earned $0.7 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

April 2015 modification: The AG-881 Agreements were determined to be a modification of the 2010 Agreement because they govern AG-881, a compound originally identified within the 2010 Agreement.

May 2016 modification: The 2016 Agreement was determined to be a modification of the 2010 Agreement and the AG-881 Agreements because it governs compounds originally identified within the 2010 Agreement, including AG-270. All undelivered elements identified under the April 2015 modification that remained undelivered at the time of the May 2016 modification are supplanted by the undelivered elements identified under the May 2016 modification.

Upon the modifications, under the provisions of ASC 605-25, Multiple Element Arrangements, we identified the remaining deliverables under the modified arrangement, and determined the best estimate of selling price, or BESP, for the undelivered elements as of the modification date. We then allocated the total arrangement consideration, which included the remaining deferred revenue balance at the modification date, any upfront payments received upon modification and other consideration under the modified arrangement that were deemed to be determinable at the modification date, to each unit of accounting relative to our BESP for each unit of accounting. The undelivered elements at the time of the modification, which are each considered by us to have stand-alone value and therefore were determined to be separate units of accounting, the related BESP, the method of recognizing the allocated consideration, and the period through which it is expected to be recognized at the time of each modification are as follows:



Undelivered Element	BESP			Unit(s) of Accounting	Principal/Agent	Recognition Method
April 2015 modification
AG-881 program licenses (1)		$33.2	million	2	Principal	Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements
On-going development services (2) (3)		$12.7	million	4	Principal	Proportionally as services are delivered over the performance period, expected to be through September 2017
On-going development services (2) (3)		$97.3	million	4	Agent	Proportionally as services are delivered over the performance period, expected to be through December 2017
On-going research and development (2)		$30.5	million	1	Principal	Ratably over the performance period, expected to be through April 2016
Committee participations (4)		$0.8	million	1	Principal	Ratably over the performance period, expected to be through December 2016
May 2016 modification (supplants undelivered elements of April 2015 modification)
On-going development services (2) (3)		$67.8	million	3	Principal	Proportionally as services are delivered over the performance period, expected to be through December 2019
On-going development services (2) (3)		$22.4	million	3	Agent	Proportionally as services are delivered over the performance period, expected to be through December 2019
On-going research and development (2)		$207.0	million	1	Principal	Ratably over the performance period, expected to be through May 2022
Committee participations (4)		$1.5	million	1	Principal	Ratably over the performance period, expected to be through December 2022
Additional development services		$48.7	million	1	Principal	Proportionally as services are delivered over the performance period, expected to begin in September 2020

(1)

The BESP 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 BESP 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 BESP and revenue recognized would vary.


(2)	The BESP 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 BESP was developed using internal full time equivalent costs to support the development services.


(4)	The BESP was developed using our management’s best estimate of the anticipated participation hours and the market rate for comparable participants.

The total estimated arrangement consideration, as well as the expected timing of revenue recognition, is adjusted based on changes in estimated arrangement consideration as a result of changes in estimates for on-going development services. The allocable consideration will increase as we perform certain services for which we are eligible to receive additional consideration. These amounts are recognized on a cumulative catch-up basis for any in-process units of accounting or immediately for any fully delivered units of accounting. The estimated arrangement consideration may decrease if we receive less reimbursement than initially estimated.

During the three and nine months ended September 30, 2017 and 2016, we recognized as collaboration revenue the following non-contingent consideration allocated to each undelivered element (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
Undelivered Element	2017		2016		2017		2016
April 2015 modification
AG-881 program licenses	$	—	$	—	$	—	$	1,356
On-going development services (principal)	—		—		—		1,656
On-going research and development	—		—		—		4,584
Committee participations	—		—		—		89
May 2016 modification
On-going development services (principal)	3,283		3,134		10,895		4,797
On-going research and development	6,425		5,814		19,479		8,516
Committee participations	41		37		124		54
Total collaboration revenue - related party	$	9,749	$	8,985	$	30,498	$	21,052

During the three and nine months ended September 30, 2017 and 2016, we recognized as a reduction of research and development expenses the following non-contingent consideration allocated to each undelivered element (in thousands):



	Modification Period	Three Months Ended September 30,				Nine Months Ended September 30,
Undelivered Element	Modification Period	2017		2016		2017		2016
On-going development services (agent)	April 2015	$	—	$	—	$	—	$	7,456
On-going development services (agent)	May 2016	1,078		3,453		6,329		4,780
Total reduction of research and development expenses		$	1,078	$	3,453	$	6,329	$	12,236

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. For the three and nine months ended September 30, 2017 and 2016, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Collaboration revenue - related party
Development activities	$	—	$	—	$	—	$	1,192
Commercialization activities	$	894	$	—	$	1,999	$	—
Reduction of research and development expenses
Development activities	$	—	$	585	$	14	$	6,518

For the three and nine months ended September 30, 2017 and 2016, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Collaboration revenue - related party	$	10,643	$	8,985	$	32,497	$	22,244
Reduction of research and development expenses	$	1,078	$	4,038	$	6,343	$	18,754

As of September 30, 2017 and December 31, 2016, we recorded a collaboration receivable of $3.5 million and $4.9 million, respectively, related to reimbursable development costs.

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

In January 2016, upon the initiation of the IDHENTIFY phase 3 study of IDHIFA®, we earned and received a milestone payment of $25.0 million, which was recognized as revenue during the three months ended March 31, 2016. No other milestones were earned during the nine months ended September 30, 2017 and 2016. The next potential milestones expected to be achieved under the Collaboration Agreements relate to specified ex-U.S. regulatory events. Achievement of these events will result in milestone payments of up to $70.0 million. Additionally, the next potential payment we expect to receive under the Collaboration Agreements is related to Celgene’s exercise of its option to develop and commercialize AG-270, the program focused on MTAP-deleted cancers. This potential exercise will result in a license fee of at least $30.0 million.

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 an undisclosed cancer metabolism target, 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 the undisclosed target. 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. Aurigene is also eligible to receive low single-digit royalties on 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 milestones 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

9 Months Ended

Sep. 30, 2017

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses consist of the following (in thousands):



	September 30, 2017		December 31, 2016
Accrued compensation	$	11,273	$	11,092
Accrued research and development costs	16,043		20,266
Accrued professional fees	3,089		476
Accrued other	355		168
Total accrued expenses	$	30,760	$	32,002

Share-Based Payments

9 Months Ended

Sep. 30, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

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, or IPO, 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 remain outstanding and effective. As of September 30, 2017, the total number of shares reserved under the 2007 Plan and the 2013 Plan are 7,407,798, and we had 1,275,813 shares available for future issuance under the 2013 Plan.

The following table presents stock option activity for the nine months ended September 30, 2017:



	Number of Stock Options		Weighted- Average Exercise Price
Outstanding at December 31, 2016	5,218,880		$	46.79
Granted	1,494,252		50.61
Exercised	(529,618	)	19.31
Forfeited/expired	(362,903	)	72.43
Outstanding at September 30, 2017	5,820,611		$	48.68
Exercisable at September 30, 2017	2,969,761		$	41.87
Vested and expected to vest at September 30, 2017	5,820,611		$	48.68

At September 30, 2017, the total unrecognized compensation expense related to unvested stock option awards was $95.7 million, which we expect to recognize over a weighted-average period of approximately 2.5 years.

Restricted stock units

We may grant awards of RSUs to non-employee directors and employees on a discretionary basis pursuant to the 2013 Plan. Each RSU entitles the holder to receive, at the end of each vesting period, a specified number of shares of our common stock.

The following table presents RSU activity for the nine months ended September 30, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	77,050		$	49.60
Granted	60,750		51.04
Vested	(7,500	)	122.22
Forfeited/expired	(10,300	)	39.76
Unvested shares at September 30, 2017	120,000		$	46.63

As of September 30, 2017, there was approximately $2.8 million of total unrecognized compensation expense related to RSUs, which we expect to be recognized over a weighted-average period of approximately 1.2 years.

Performance-based stock options

During the nine months ended September 30, 2017 and 2016, no options to purchase shares of common stock that contain performance-based or a combination of performance-based and service-based vesting criteria were granted by us. However, certain performance-based stock options issued in prior periods were still outstanding as of September 30, 2017. Performance-based vesting criteria for options primarily relate to milestone events specific to our corporate goals, including but not limited to certain preclinical, clinical and regulatory development milestones related to our product candidates. Stock-based compensation expense associated with these performance-based stock options is recognized if the performance condition is considered probable of achievement using our management’s best estimates. As of September 30, 2017, all performance-based milestones had been achieved and all expense related to these options has been recorded.

Performance-based stock units

We may grant awards of PSUs to non-employee directors and employees on a discretionary basis pursuant to the 2013 Plan. Each PSU entitles the holder to receive, at the achievement of the performance-based and service-based vesting criteria, a specified number of shares of our common stock. Performance-based vesting criteria primarily relate to milestone events specific to our corporate goals, specifically regulatory milestones related to our product candidates.

The following table presents PSU activity for the nine months ended September 30, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	200,613		$	53.36
Granted	16,391		50.83
Vested	—		—
Forfeited/expired	(25,630	)	51.00
Unvested shares at September 30, 2017	191,374		$	53.46

Stock-based compensation expense associated with these PSUs is recognized if the performance condition is considered probable of achievement using our management’s best estimates. As of September 30, 2017, there was approximately $10.2 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. The 2013 ESPP is administered by our Board of Directors or by a committee appointed by our Board of Directors. Under the 2013 ESPP, each offering period is six months, at the end of which employees may purchase shares of common stock through payroll deductions made over the term of the offering period. The per-share purchase price at the end of each offering period is equal to 85% of the closing price of one share of our common stock at the beginning or end of the offering period, whichever is lower, subject to Internal Revenue Service limits. We issued 59,651 shares and 36,680 shares during the nine months ended September 30, 2017 and 2016, 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 September 30, 2017, we had 213,791 shares available for future issuance under the 2013 ESPP.

Stock-based compensation expense

During the three and nine months ended September 30, 2017 and 2016, we recorded stock-based compensation expense for employee and non-employee stock options, RSUs, performance-based stock options and ESPP shares. Stock-based compensation expense by award type included within the condensed consolidated statements of operations is as follows (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Stock options	$	11,330	$	11,425	$	32,315	$	30,288
Restricted stock units	634		510		2,104		1,367
Performance-based stock options	—		—		—		46
Employee Stock Purchase Plan	243		208		709		545
Total stock-based compensation expense	$	12,207	$	12,143	$	35,128	$	32,246

Expenses related to equity-based awards were allocated as follows in the condensed consolidated statements of operations (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development expense	$	7,620	$	7,903	$	22,835	$	19,992
General and administrative expense	4,587		4,240		12,293		12,254
Total stock-based compensation expense	$	12,207	$	12,143	$	35,128	$	32,246

Loss per Share

9 Months Ended

Sep. 30, 2017

Earnings Per Share [Abstract]

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. Furthermore, performance-based stock units with vesting conditions that were not met as of September 30, 2017 are excluded as 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 for the periods indicated because including them would have had an anti-dilutive effect:



	Three and Nine Months Ended September 30,
	2017	2016
Stock options	5,820,611	5,431,068
Restricted stock units	120,000	66,300
Employee Stock Purchase Plan options	5,348	5,977
Total common stock equivalents	5,945,959	5,503,345

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The condensed consolidated balance sheet as of September 30, 2017, and the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2017 and 2016, and cash flows for the nine months ended September 30, 2017 and 2016, 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 September 30, 2017, and our results of operations for the three and nine months ended September 30, 2017 and 2016, and cash flows for the nine months ended September 30, 2017 and 2016. The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three and nine-month period are also unaudited. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results to be expected for the year ending December 31, 2017 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, 2016 that was filed with the Securities and Exchange Commission, or the SEC, on February 16, 2017. Our consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, Agios Securities Corporation and Agios International Sarl. 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 In the quarter ended March 31, 2017, we adopted Accounting Standards Update, or ASU, 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, or ASU 2016-09, which simplifies several aspects of the accounting for employee share-based payment transactions. There have been no other material changes to the significant accounting policies previously disclosed in our Annual Report on Form 10-K for the year ended December 31, 2016. Recent accounting pronouncements 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. 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; and 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, or collectively, the Revenue ASUs. The Revenue ASUs provide an accounting standard for a single comprehensive model for use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The accounting standard is effective for interim and annual periods beginning after December 15, 2017, with an option to early adopt for interim and annual periods beginning after December 15, 2016. 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 will adopt the new standard effective January 1, 2018 under the modified retrospective method. We have allocated internal resources to the implementation and are in the process of determining the impact of the Revenue ASUs on our financial statements; however, the adoption of the Revenue ASUs may have a material impact on revenue recognition, our notes to consolidated financial statements and our internal controls over financial reporting. As discussed further in detail within Note 5, Collaboration Agreements, our collaboration agreements with Celgene Corporation, or Celgene, are currently our sole source of revenue and the only arrangements impacted by the adoption of the Revenue ASUs. Other Recent Accounting Pronouncements In May 2017, the FASB issued ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting, or ASU 2017-09, which provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in the Accounting Standards Codification, or ASC, 718. ASU 2017-09 is effective for us for annual periods beginning after December 15, 2017, and interim periods therein, with early adoption permitted. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory, or ASU 2016-16, which removes the prohibition in ASC 740, Income Taxes, against the immediate recognition of the current and deferred income tax effects of intra-entity transfers of assets other than inventory. ASU 2016-16 is effective for us for annual periods beginning after December 15, 2017, and interim periods therein, with early adoption permitted. We are currently in the process of evaluating the impact of the guidance on our consolidated financial statements. 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 is effective for us for annual periods beginning after December 15, 2018 and interim periods therein, with early adoption permitted. 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	Marketable securities at September 30, 2017 and December 31, 2016 consisted of investments in certificates of deposit, U.S. Treasuries, government securities and corporate debt securities. We determine the appropriate classification of the securities at the time they are acquired and evaluate the appropriateness of such classifications at each balance sheet date. We classify our marketable securities as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities. Marketable securities 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. At September 30, 2017 and December 31, 2016, 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. We review marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairments of investments are recognized in the condensed consolidated statements of operations if we experience a credit loss, have the intent to sell the marketable security, or if it is more likely than not that we will be required to sell the marketable security before recovery of the amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with our investment policy, the severity and the duration of the impairment, and changes in value subsequent to the end of the period.
Collaboration Revenue	Upon the modifications, under the provisions of ASC 605-25, Multiple Element Arrangements, we identified the remaining deliverables under the modified arrangement, and determined the best estimate of selling price, or BESP, for the undelivered elements as of the modification date. We then allocated the total arrangement consideration, which included the remaining deferred revenue balance at the modification date, any upfront payments received upon modification and other consideration under the modified arrangement that were deemed to be determinable at the modification date, to each unit of accounting relative to our BESP for each unit of accounting.
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. Furthermore, performance-based stock units with vesting conditions that were not met as of September 30, 2017 are excluded as 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.

- Definition

Disclosure of accounting policy for investments in debt and equity securities that have readily determinable fair values (marketable securities). At a minimum, the disclosure might address accounting policies for investments classified as trading, available for sale, or held to maturity and may include how the entity determines whether impairments of available for sale or held to maturity investments are other than temporary, how the fair values of the entity's securities are determined, and the entity's accounting treatment for transfers between investment categories.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 5.M)
-URI http://asc.fasb.org/extlink&oid=65877573&loc=d3e87990-122713

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84158767&loc=d3e18780-107790

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section S50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6381980&loc=d3e87707-122711

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62652-112803

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(5))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

- Definition

Disclosure of accounting policy for revenue recognition for multiple-deliverable arrangements including, at a minimum (as applicable): (1) the nature of such arrangements, (2) the significant deliverables within the arrangements, (3) the general timing of delivery or performance of service for the deliverables within the arrangements, (4) performance-, cancellation-, termination- or refund-type provisions, (5) a discussion of the significant factors, inputs, assumptions, and methods used to determine selling price (whether vendor-specific objective evidence, third-party evidence, or estimated selling price) for the significant deliverables, (6) whether the significant deliverables in the arrangements qualify as separate units of accounting and the reasons that they do not qualify as separate units of accounting, if applicable, and (7) the general timing of revenue recognition for significant units of accounting. This element is applicable to all multiple-deliverable arrangements, including software arrangements (for example, software products, upgrades or enhancements, postcontract customer support, or services).

+ References + Details

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2017

Fair Value Disclosures [Abstract]

Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis

The following table summarizes the cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2017 (in thousands):



	Level 1		Level 2		Level 3		Total
Cash equivalents	$	88,556	$	19,993	$	—	$	108,549
Marketable securities:
Certificates of deposit	—		11,185		—		11,185
U.S. Treasuries	151,814		—		—		151,814
Government securities	53,131		13,701		—		66,832
Corporate debt securities	—		279,160		—		279,160
Total cash equivalents and marketable securities	$	293,501	$	324,039	$	—	$	617,540

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities at September 30, 2017 consist of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	10,240	$	1	$	(10	)	$	10,231
U.S Treasuries	113,824		4		(45		)	113,783
Government securities	42,443		—		(32		)	42,411
Corporate debt securities	208,850		3		(91		)	208,762
Non-current:
Certificates of deposit	960		—		(6		)	954
U.S Treasuries	38,162		—		(131		)	38,031
Government securities	24,492		—		(71		)	24,421
Corporate debt securities	70,535		2		(139		)	70,398
	$	509,506	$	10	$	(525	)	$	508,991

Marketable securities at December 31, 2016 consist of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	11,280	$	2	$	(3	)	$	11,279
U.S. Treasuries	141,678		2		(62		)	141,618
Government securities	19,533		—		(23		)	19,510
Corporate debt securities	208,285		3		(135		)	208,153
Non-current:
Certificates of deposit	7,600		6		(13		)	7,593
Government securities	4,499		—		(21		)	4,478
Corporate debt securities	20,248		—		(69		)	20,179
	$	413,123	$	13	$	(326	)	$	412,810

Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2017

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

Summary of Multiple-deliverable Arrangements Revenue

The undelivered elements at the time of the modification, which are each considered by us to have stand-alone value and therefore were determined to be separate units of accounting, the related BESP, the method of recognizing the allocated consideration, and the period through which it is expected to be recognized at the time of each modification are as follows:



Undelivered Element	BESP			Unit(s) of Accounting	Principal/Agent	Recognition Method
April 2015 modification
AG-881 program licenses (1)		$33.2	million	2	Principal	Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements
On-going development services (2) (3)		$12.7	million	4	Principal	Proportionally as services are delivered over the performance period, expected to be through September 2017
On-going development services (2) (3)		$97.3	million	4	Agent	Proportionally as services are delivered over the performance period, expected to be through December 2017
On-going research and development (2)		$30.5	million	1	Principal	Ratably over the performance period, expected to be through April 2016
Committee participations (4)		$0.8	million	1	Principal	Ratably over the performance period, expected to be through December 2016
May 2016 modification (supplants undelivered elements of April 2015 modification)
On-going development services (2) (3)		$67.8	million	3	Principal	Proportionally as services are delivered over the performance period, expected to be through December 2019
On-going development services (2) (3)		$22.4	million	3	Agent	Proportionally as services are delivered over the performance period, expected to be through December 2019
On-going research and development (2)		$207.0	million	1	Principal	Ratably over the performance period, expected to be through May 2022
Committee participations (4)		$1.5	million	1	Principal	Ratably over the performance period, expected to be through December 2022
Additional development services		$48.7	million	1	Principal	Proportionally as services are delivered over the performance period, expected to begin in September 2020

(1)


(2)	The BESP 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 BESP was developed using internal full time equivalent costs to support the development services.


(4)	The BESP was developed using our management’s best estimate of the anticipated participation hours and the market rate for comparable participants.

For the three and nine months ended September 30, 2017 and 2016, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Collaboration revenue - related party
Development activities	$	—	$	—	$	—	$	1,192
Commercialization activities	$	894	$	—	$	1,999	$	—
Reduction of research and development expenses
Development activities	$	—	$	585	$	14	$	6,518



	Modification Period	Three Months Ended September 30,				Nine Months Ended September 30,
Undelivered Element	Modification Period	2017		2016		2017		2016
On-going development services (agent)	April 2015	$	—	$	—	$	—	$	7,456
On-going development services (agent)	May 2016	1,078		3,453		6,329		4,780
Total reduction of research and development expenses		$	1,078	$	3,453	$	6,329	$	12,236

For the three and nine months ended September 30, 2017 and 2016, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):



	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Collaboration revenue - related party	$	10,643	$	8,985	$	32,497	$	22,244
Reduction of research and development expenses	$	1,078	$	4,038	$	6,343	$	18,754



	Three Months Ended September 30,				Nine Months Ended September 30,
Undelivered Element	2017		2016		2017		2016
April 2015 modification
AG-881 program licenses	$	—	$	—	$	—	$	1,356
On-going development services (principal)	—		—		—		1,656
On-going research and development	—		—		—		4,584
Committee participations	—		—		—		89
May 2016 modification
On-going development services (principal)	3,283		3,134		10,895		4,797
On-going research and development	6,425		5,814		19,479		8,516
Committee participations	41		37		124		54
Total collaboration revenue - related party	$	9,749	$	8,985	$	30,498	$	21,052

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2017

Payables and Accruals [Abstract]

Summary of Accrued Expenses

Accrued expenses consist of the following (in thousands):



	September 30, 2017		December 31, 2016
Accrued compensation	$	11,273	$	11,092
Accrued research and development costs	16,043		20,266
Accrued professional fees	3,089		476
Accrued other	355		168
Total accrued expenses	$	30,760	$	32,002

Share-Based Payments (Tables)

9 Months Ended

Sep. 30, 2017

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 nine months ended September 30, 2017:



	Number of Stock Options		Weighted- Average Exercise Price
Outstanding at December 31, 2016	5,218,880		$	46.79
Granted	1,494,252		50.61
Exercised	(529,618	)	19.31
Forfeited/expired	(362,903	)	72.43
Outstanding at September 30, 2017	5,820,611		$	48.68
Exercisable at September 30, 2017	2,969,761		$	41.87
Vested and expected to vest at September 30, 2017	5,820,611		$	48.68

Unvested Stock Unit Activity

The following table presents RSU activity for the nine months ended September 30, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	77,050		$	49.60
Granted	60,750		51.04
Vested	(7,500	)	122.22
Forfeited/expired	(10,300	)	39.76
Unvested shares at September 30, 2017	120,000		$	46.63

Schedule of Performance-Based Units

The following table presents PSU activity for the nine months ended September 30, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	200,613		$	53.36
Granted	16,391		50.83
Vested	—		—
Forfeited/expired	(25,630	)	51.00
Unvested shares at September 30, 2017	191,374		$	53.46

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 September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Stock options	$	11,330	$	11,425	$	32,315	$	30,288
Restricted stock units	634		510		2,104		1,367
Performance-based stock options	—		—		—		46
Employee Stock Purchase Plan	243		208		709		545
Total stock-based compensation expense	$	12,207	$	12,143	$	35,128	$	32,246

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 September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Research and development expense	$	7,620	$	7,903	$	22,835	$	19,992
General and administrative expense	4,587		4,240		12,293		12,254
Total stock-based compensation expense	$	12,207	$	12,143	$	35,128	$	32,246

Loss per Share (Tables)

9 Months Ended

Sep. 30, 2017

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 for the periods indicated because including them would have had an anti-dilutive effect:



	Three and Nine Months Ended September 30,
	2017	2016
Stock options	5,820,611	5,431,068
Restricted stock units	120,000	66,300
Employee Stock Purchase Plan options	5,348	5,977
Total common stock equivalents	5,945,959	5,503,345

Overview and Basis of Presentation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Apr. 30, 2017	Sep. 30, 2017	Sep. 30, 2016
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	5,808,080
Proceeds from public offering of common stock, net of commissions	$ 270,200	$ 270,250	$ 162,150
Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	5,050,505
Offer price (in usd per share)	$ 49.50
Proceeds from public offering of common stock, net of commissions	$ 235,000
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	757,575
Proceeds from public offering of common stock, net of commissions	$ 35,200

Fair Value Measurements - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	$ 508,991	$ 412,810
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	108,549
Total cash equivalents and marketable securities	617,540
Fair Value, Measurements, Recurring \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	11,185
Fair Value, Measurements, Recurring \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	151,814
Fair Value, Measurements, Recurring \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	66,832
Fair Value, Measurements, Recurring \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	279,160
Fair Value, Measurements, Recurring \| Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	88,556
Total cash equivalents and marketable securities	293,501
Fair Value, Measurements, Recurring \| Level 1 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 1 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	151,814
Fair Value, Measurements, Recurring \| Level 1 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	53,131
Fair Value, Measurements, Recurring \| Level 1 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	19,993
Total cash equivalents and marketable securities	324,039
Fair Value, Measurements, Recurring \| Level 2 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	11,185
Fair Value, Measurements, Recurring \| Level 2 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 2 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	13,701
Fair Value, Measurements, Recurring \| Level 2 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	279,160
Fair Value, Measurements, Recurring \| Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Total cash equivalents and marketable securities	0
Fair Value, Measurements, Recurring \| Level 3 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 3 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 3 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Fair Value, Measurements, Recurring \| Level 3 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	$ 0

Fair Value Measurements - Additional Information (Detail)	Sep. 30, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers of assets from Level 1 to Level 2	$ 4,000,000
Transfers of assets from Level 2 to Level 1	10,000,000
Transfers of liabilities from Level 1 to Level 2	0
Transfers of liabilities from Level 2 to Level 1	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets (liabilities)	$ 0

Marketable Securities - Additional Information (Detail)	3 Months Ended		9 Months Ended
Marketable Securities - Additional Information (Detail)	Sep. 30, 2017 USD ($) Securities	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Securities	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) Securities
Schedule of Available-for-sale Securities [Line Items]
Realized gain loss) on marketable securities	$ 0	$ 0	$ 0	$ 0
Reclassifications out of accumulated other comprehensive income	$ 0	$ 0	$ 0	$ 0
Established time period for liquidation	12 months
Debt securities in an unrealized loss position \| Securities	238		238		158
Aggregate fair value of debt securities in an unrealized loss position	$ 435,500,000		$ 435,500,000		$ 335,400,000
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 of Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 509,506	$ 413,123
Unrealized Gains	10	13
Unrealized Losses	(525)	(326)
Fair Value	508,991	412,810
Current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,240	11,280
Unrealized Gains	1	2
Unrealized Losses	(10)	(3)
Fair Value	10,231	11,279
Current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	113,824	141,678
Unrealized Gains	4	2
Unrealized Losses	(45)	(62)
Fair Value	113,783	141,618
Current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,443	19,533
Unrealized Gains	0	0
Unrealized Losses	(32)	(23)
Fair Value	42,411	19,510
Current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	208,850	208,285
Unrealized Gains	3	3
Unrealized Losses	(91)	(135)
Fair Value	208,762	208,153
Non-current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	960	7,600
Unrealized Gains	0	6
Unrealized Losses	(6)	(13)
Fair Value	954	7,593
Non-current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	38,162
Unrealized Gains	0
Unrealized Losses	(131)
Fair Value	38,031
Non-current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,492	4,499
Unrealized Gains	0	0
Unrealized Losses	(71)	(21)
Fair Value	24,421	4,478
Non-current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	70,535	20,248
Unrealized Gains	2	0
Unrealized Losses	(139)	(69)
Fair Value	$ 70,398	$ 20,179

Collaboration Agreements - 2016 Agreement (Details) - 2016 Agreement	1 Months Ended
	May 31, 2016 Program special_case_extension	May 17, 2016 special_case_extension
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of programs that may be designated for continued development for which development candidates have yet to be nominated	3
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of cancer metabolism programs discovered under previous agreement, now governed by current agreement	2
Initial research term	4 years
Extension period	2 years
Number of allowable special case extensions \| special_case_extension	4	4
Special case extension term	1 year

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 - Financial Terms (Details) - Celgene - 2016 Agreement	1 Months Ended	3 Months Ended
	May 31, 2016 USD ($) special_case_extension	Mar. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	May 17, 2016 USD ($) special_case_extension
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 200,000,000.0	$ 8,000,000.0
Extension period	2 years
Number of allowable special case extensions \| special_case_extension	4			4
Upfront payment agreement extension fee receivable	$ 40,000,000.0
Option exercise fee receivable			$ 30,000,000	$ 30,000,000.0
Additional option exercise fee for further development				10,000,000.0
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum option exercise fee receivable for continuation program				$ 35,000,000

Collaboration Agreements - Summary of Milestone-based Receivable Payments (Details) - Celgene $ in Millions	May 31, 2016 USD ($)
Specified clinical development event \| Co Commercial Agreement
Revenue Recognition, Milestone Method [Line Items]
Milestone-based receivable payments, eligible to be received	$ 25.0
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	25.0
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	20.0
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	$ 125.0

Collaboration Agreements - AG-881 Agreements (Details) - AG-881 program licenses - USD ($)	1 Months Ended
	May 31, 2015	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
Milestone payments upon achievement of specified regulatory milestone events		$ 55,000,000

Collaboration Agreements - 2010 Agreement (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jul. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty revenue	$ 715,000	$ 0	$ 715,000	$ 0
2010 Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone-based receivable payments, eligible to be received					$ 95,000,000
Milestone payments upon achievement of specified regulatory milestone events	$ 70,000,000		$ 70,000,000		70,000,000
Milestone payment upon achievement of a specified commercial milestone event					$ 25,000,000

Collaboration Agreements - Summary of the Method of Recognizing the Allocated Consideration Upon Each Modification (Details) $ in Millions	1 Months Ended
	May 31, 2016 USD ($) unit_of_accounting	Apr. 30, 2015 USD ($) unit_of_accounting
Program Licenses \| April 2015 modification \| Upon Execution of Agreement \| AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 33.2
Unit(s) of Accounting \| unit_of_accounting		2
On-going development services (principal) \| April 2015 modification \| Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 12.7
Unit(s) of Accounting \| unit_of_accounting		4
On-going development services (principal) \| April 2015 modification \| Ratably over the performance period, expected to be through April 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 30.5
Unit(s) of Accounting \| unit_of_accounting		1
On-going development services (principal) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through December 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 67.8
Unit(s) of Accounting \| unit_of_accounting	3
On-going development services (principal) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through May 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 207.0
Unit(s) of Accounting \| unit_of_accounting	1
On-going development services (agent) \| April 2015 modification \| Proportionally as services are delivered over the performance period, expected to be through September 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 97.3
Unit(s) of Accounting \| unit_of_accounting		4
On-going development services (agent) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Proportionally as services are delivered over the performance period, expected to be through 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 22.4
Unit(s) of Accounting \| unit_of_accounting	3
Committee participations \| April 2015 modification \| Proportionally as services are delivered over the performance period, expected to be through December 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 0.8
Unit(s) of Accounting \| unit_of_accounting		1
Committee participations \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through December 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 1.5
Unit(s) of Accounting \| unit_of_accounting	1
Additional development services \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Proportionally as services are delivered over the performance period, expected to begin in September 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 48.7
Unit(s) of Accounting \| unit_of_accounting	1

Collaboration Agreements - Summary of Collaboration Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 11,358	$ 8,985	$ 33,212	$ 47,244
Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	9,749	8,985	30,498	21,052
Program Licenses \| AG-881 program licenses \| April 2015 modification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	0	0	1,356
On-going development services (principal) \| Collaborative arrangement, product \| April 2015 modification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	0	0	1,656
On-going development services (principal) \| Collaborative arrangement, product \| May 2016 modification (supplants undelivered elements of April 2015 modification)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	3,283	3,134	10,895	4,797
On-going research and development \| Collaborative arrangement, product \| April 2015 modification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	0	0	4,584
On-going research and development \| Collaborative arrangement, product \| May 2016 modification (supplants undelivered elements of April 2015 modification)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	6,425	5,814	19,479	8,516
Committee participations \| Collaborative arrangement, product \| April 2015 modification
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	0	0	89
Committee participations \| Collaborative arrangement, product \| May 2016 modification (supplants undelivered elements of April 2015 modification)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 41	$ 37	$ 124	$ 54

Collaboration Agreements - Summary Of Revenue Recognized As A Reduction Of Research And Development Expenses (Details) - Research and development expense - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	$ 1,078	$ 3,453	$ 6,329	$ 12,236
April 2015 modification \| On-going development services (agent)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	0	0	0	7,456
May 2016 modification (supplants undelivered elements of April 2015 modification) \| On-going development services (agent)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	$ 1,078	$ 3,453	$ 6,329	$ 4,780

Collaboration Agreements - Development and Commercialization Expense Not Contemplated As Part Of Modifications (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 11,358	$ 8,985	$ 33,212	$ 47,244
Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	9,749	8,985	30,498	21,052
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Development Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	0	0	1,192
Total reduction of research and development expenses	0	585	14	6,518
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 894	$ 0	$ 1,999	$ 0

Collaboration Agreements - Collaboration Revenue and Research and Development Expense Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Revenue Recognition and Deferred Revenue [Abstract]
Collaboration revenue - related party	$ 10,643	$ 8,985	$ 32,497	$ 22,244
Reduction of research and development expenses	1,078	$ 4,038	6,343	$ 18,754
Collaboration receivable	$ 3,489		$ 3,489		$ 4,886

Collaboration Agreements - Accounting Analysis And Revenue Recognition - Milestone (Details) - USD ($)	3 Months Ended	9 Months Ended
	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	May 17, 2016	Jul. 31, 2014
IDHIFA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue	$ 25,000,000	$ 0.0	$ 0.0
Master Research And Collaboration Agreement \| Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Option exercise fee receivable		30,000,000		$ 30,000,000.0
2010 Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments upon achievement of specified regulatory milestone events		$ 70,000,000			$ 70,000,000

Collaboration Agreements - Aurigene Discovery Technologies Limited (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Apr. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 72,917	$ 60,643	$ 215,465	$ 155,485
Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 3,000
Potential future milestone payments						$ 17,000

Accrued Expenses - Summary of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued compensation	$ 11,273	$ 11,092
Accrued research and development costs	16,043	20,266
Accrued professional fees	3,089	476
Accrued other	355	168
Total	$ 30,760	$ 32,002

Share-Based Payments - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	1,494,252
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 2.8
Weighted-average period to recognize compensation expense (in years)	1 year 2 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)	7,407,798
Shares available for future issuance (in shares)	1,275,813
2013 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 95.7
Weighted-average period to recognize compensation expense (in years)	2 years 5 months 23 days
2013 Stock Incentive Plan \| Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)	0	0
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	$ 10.2
2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)	213,791
Purchase price discount rate stock option	85.00%
Shares issued under 2013 ESPP (in shares)	59,651	36,680
Opportunity to purchase of common stock (in shares)	327,272

Share-Based Payments - Summary of Company's Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Stock Options, Outstanding, Beginning balance (in shares) \| shares	5,218,880
Number of Stock Options, Granted (in shares) \| shares	1,494,252
Number of Stock Options, Exercised (in shares) \| shares	(529,618)
Number of Stock Options, Forfeited/Expired (in shares) \| shares	(362,903)
Number of Stock Options, Outstanding, Ending balance (in shares) \| shares	5,820,611
Number of Stock Options, Exercisable (in shares) \| shares	2,969,761
Number of Stock Options, Vested and expected to vest (in shares) \| shares	5,820,611
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	$ 46.79
Weighted-Average Exercise Price, Granted (in usd per share) \| $ / shares	50.61
Weighted-Average Exercise Price, Exercised (in usd per share) \| $ / shares	19.31
Weighted-Average Exercise Price, Forfeited/Expired (in usd per share) \| $ / shares	72.43
Weighted-Average Exercise Price, Outstanding, Ending balance (in usd per share) \| $ / shares	48.68
Weighted-Average Exercise Price, Exercisable (in usd per share) \| $ / shares	41.87
Weighted-Average Exercise Price, Vested and expected to vest (in usd per share) \| $ / shares	$ 48.68

Share-Based Payments - Summary of Unvested RSUs Activity (Detail) - Restricted stock units	9 Months Ended
	Sep. 30, 2017 $ / shares shares
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	77,050
Granted (in shares) \| shares	60,750
Vested (in shares) \| shares	(7,500)
Forfeited/expired (in shares) \| shares	(10,300)
Unvested shares end of period (in shares) \| shares	120,000
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	$ 49.60
Weighted-average grant date fair value, Granted (in usd per share) \| $ / shares	51.04
Weighted-average grant date fair value, Vested (in usd per share) \| $ / shares	122.22
Weighted-average grant date fair value, Forfeited/expired (in usd per share) \| $ / shares	39.76
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) \| $ / shares	$ 46.63

Share-Based Payments - Schedule of Performance-Based Units (Detail) - Performance-Based Stock Units (PSUs)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
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	200,613
Granted (in shares) \| shares	16,391
Vested (in shares) \| shares	0
Forfeited/expired (in shares) \| shares	(25,630)
Unvested shares end of period (in shares) \| shares	191,374
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	$ 53.36
Weighted-average grant date fair value, Granted (in usd per share) \| $ / shares	50.83
Weighted-average grant date fair value, Vested (in usd per share) \| $ / shares	0.00
Weighted-average grant date fair value, Forfeited/expired (in usd per share) \| $ / shares	51.00
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) \| $ / shares	$ 53.46

Share-Based Payments - Schedule of Stock-Based Compensation Expense by Award Type Included Within the Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 12,207	$ 12,143	$ 35,128	$ 32,246
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	11,330	11,425	32,315	30,288
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	634	510	2,104	1,367
Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0	0	0	46
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 243	$ 208	$ 709	$ 545

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 (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 12,207	$ 12,143	$ 35,128	$ 32,246
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	7,620	7,903	22,835	19,992
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,587	$ 4,240	$ 12,293	$ 12,254

Loss per Share - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,945,959	5,503,345	5,945,959	5,503,345
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,820,611	5,431,068	5,820,611	5,431,068
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)	120,000	66,300	120,000	66,300
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)	5,348	5,977	5,348	5,977

Collaboration Agreements - Summary of the Method of Recognizing the Allocated Consideration Upon Each Modification (Details) $ in Millions	1 Months Ended
	May 31, 2016 USD ($) unit_of_accounting	Apr. 30, 2015 USD ($) unit_of_accounting
Program Licenses \| April 2015 modification \| Upon Execution of Agreement \| AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 33.2
Unit(s) of Accounting \| unit_of_accounting		2
On-going development services (principal) \| April 2015 modification \| Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 12.7
Unit(s) of Accounting \| unit_of_accounting		4
On-going development services (principal) \| April 2015 modification \| Ratably over the performance period, expected to be through April 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 30.5
Unit(s) of Accounting \| unit_of_accounting		1
On-going development services (principal) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through December 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 67.8
Unit(s) of Accounting \| unit_of_accounting	3
On-going development services (principal) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through May 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 207.0
Unit(s) of Accounting \| unit_of_accounting	1
On-going development services (agent) \| April 2015 modification \| Proportionally as services are delivered over the performance period, expected to be through September 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 97.3
Unit(s) of Accounting \| unit_of_accounting		4
On-going development services (agent) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Proportionally as services are delivered over the performance period, expected to be through 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 22.4
Unit(s) of Accounting \| unit_of_accounting	3
Committee participations \| April 2015 modification \| Proportionally as services are delivered over the performance period, expected to be through December 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $		$ 0.8
Unit(s) of Accounting \| unit_of_accounting		1
Committee participations \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Ratably over the performance period, expected to be through December 2022
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 1.5
Unit(s) of Accounting \| unit_of_accounting	1
Additional development services \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Proportionally as services are delivered over the performance period, expected to begin in September 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $	$ 48.7
Unit(s) of Accounting \| unit_of_accounting	1