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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Feb. 09, 2018	Jun. 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-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus (i.e. Q1,Q2,Q3,FY)	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		57,326,741
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,154,093,268

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 102,724	$ 160,754
Marketable securities	321,212	380,560
Collaboration receivable – related party	2,448	4,886
Royalty receivable – related party	1,222	0
Tenant improvement and other receivables	169	3,428
Prepaid expenses and other current assets	17,486	10,264
Total current assets	445,261	559,892
Marketable securities	143,814	32,250
Property and equipment, net	24,431	25,337
Other non-current assets	891	1,615
Total assets	614,397	619,094
Current liabilities:
Accounts payable	22,767	17,106
Accrued expenses	34,031	32,002
Deferred revenue – related party	37,842	35,913
Deferred rent	301	3,412
Total current liabilities	94,941	88,433
Deferred revenue, net of current portion – related party	125,798	154,297
Deferred rent, net of current portion	18,155	17,773
Total liabilities	238,894	260,503
Commitments and contingent liabilities (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized, no shares issued and outstanding at December 31, 2017 and 2016	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized and 48,826,153 and 42,220,444 shares issued and outstanding at December 31, 2017 and 2016, respectively	49	42
Additional paid-in capital	1,174,904	842,013
Accumulated other comprehensive loss	(1,389)	(313)
Accumulated deficit	(798,061)	(483,151)
Total stockholders’ equity	375,503	358,591
Total liabilities and stockholders’ equity	$ 614,397	$ 619,094

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 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)	48,826,153	42,220,444
Common stock, shares outstanding (in shares)	48,826,153	42,220,444

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Collaboration revenue – related party	$ 41,074	$ 69,892	$ 59,119
Royalty revenue – related party	1,937	0	0
Total revenue	43,011	69,892	59,119
Operating expenses:
Research and development (net of $7,811, $19,714 and $25,173 of cost reimbursement from related party for the years ended December 31, 2017, 2016 and 2015, respectively)	292,681	220,163	141,827
General and administrative	71,124	50,714	35,992
Total operating expenses	363,805	270,877	177,819
Loss from operations	(320,794)	(200,985)	(118,700)
Interest income	6,124	2,514	968
Net loss	$ (314,670)	$ (198,471)	$ (117,732)
Net loss per share - basic and diluted (in usd per share)	$ (6.75)	$ (5.07)	$ (3.15)
Weighted-average number of common shares used in computing net loss per share - basic and diluted (in shares)	46,587,631	39,126,400	37,429,262

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Reduction of research and development costs	$ 7,811	$ 19,714	$ 25,173

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (314,670)	$ (198,471)	$ (117,732)
Other comprehensive (loss) income:
Unrealized (loss) gain on available-for-sale securities	(1,076)	5	(261)
Comprehensive loss	$ (315,746)	$ (198,466)	$ (117,993)

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2014		37,100,513
Beginning balance at Dec. 31, 2014	$ 424,366	$ 37	$ 591,334	$ (57)	$ (166,948)
Unrealized (loss) gain on available-for-sale securities	(261)			(261)	0
Net loss	(117,732)				(117,732)
Stock-based compensation expense	31,574		31,574
Vesting of restricted stock (in shares)		8,522
Vesting of restricted stock	6		6
Issuance of common stock upon exercise of stock options and employee stock purchase plan (in shares)		587,467
Issuance of common stock under stock incentive and employee stock purchase plans	7,136	$ 1	7,135
Issuance of common stock for follow-on offering	29		29
Ending balance (in shares) at Dec. 31, 2015		37,696,502
Ending balance at Dec. 31, 2015	345,118	$ 38	630,078	(318)	(284,680)
Unrealized (loss) gain on available-for-sale securities	5			5	0
Net loss	(198,471)				(198,471)
Stock-based compensation expense	42,086		42,086
Issuance of common stock upon exercise of stock options and employee stock purchase plan (in shares)		647,539
Issuance of common stock under stock incentive and employee stock purchase plans	7,703	$ 0	7,703
Issuance of common stock for follow-on offering (in shares)		3,876,403
Issuance of common stock for follow-on offering	162,150	$ 4	162,146
Ending balance (in shares) at Dec. 31, 2016		42,220,444
Ending balance at Dec. 31, 2016	358,591	$ 42	842,013	(313)	(483,151)
Unrealized (loss) gain on available-for-sale securities	(1,076)			(1,076)	0
Net loss	(314,670)				(314,670)
Stock-based compensation expense	$ 47,809		47,809
Vesting of restricted stock (in shares)	7,500
Issuance of common stock upon exercise of stock options and employee stock purchase plan (in shares)	730,478	797,629
Issuance of common stock under stock incentive and employee stock purchase plans	$ 14,190	$ 1	14,189
Issuance of common stock for follow-on offering (in shares)		5,808,080
Issuance of common stock for follow-on offering	270,250	$ 6	270,244
Other	409		649		(240)
Ending balance (in shares) at Dec. 31, 2017		48,826,153
Ending balance at Dec. 31, 2017	$ 375,503	$ 49	$ 1,174,904	$ (1,389)	$ (798,061)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (314,670)	$ (198,471)	$ (117,732)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation	6,432	5,708	3,342
Loss on disposal of property and equipment	40	0	33
Stock-based compensation expense	47,809	42,086	31,963
Net (accretion of discount) amortization of premium on marketable securities	(11)	773	539
Changes in operating assets and liabilities:
Collaboration receivable – related party	2,438	3,339	(1,733)
Royalty receivable – related party	(1,222)	0	0
Tenant improvement and other receivables	2,930	275	(1,040)
Prepaid expenses and other current and non-current assets	(6,530)	(2,695)	(3,768)
Accounts payable	5,329	3,501	4,215
Accrued expenses	1,522	16,854	1,633
Deferred revenue – related party	(26,570)	165,846	(14,047)
Deferred rent	(2,729)	1,346	15,805
Refundable income taxes and income taxes payable		0	3,841
Net cash (used in) provided by operating activities	(285,232)	38,562	(76,949)
Net cash (used in) provided by operating activities
Purchases of marketable securities	(688,702)	(506,067)	(353,177)
Proceeds from maturities and sales of marketable securities	635,421	396,632	501,650
Purchases of property and equipment	(4,627)	(9,915)	(20,164)
Net cash (used in) provided by investing activities	(57,908)	(119,350)	128,309
Financing activities
Proceeds from public offering of common stock, net of commissions	270,250	162,150	0
Reimbursement (payment) of public offering costs	638	(230)	(207)
Net proceeds from stock option exercises and employee stock purchase plan, and vesting of restricted stock units	14,222	7,858	6,580
Net cash provided by financing activities	285,110	169,778	6,373
Net change in cash and cash equivalents	(58,030)	88,990	57,733
Cash and cash equivalents at beginning of the period	160,754	71,764	14,031
Cash and cash equivalents at end of the period	102,724	160,754	71,764
Supplemental disclosure of non-cash investing and financing transactions:
Vesting of restricted stock		0	6
Additions to property and equipment in accounts payable and accrued expenses	1,011	73	2,163
Proceeds from stock option exercises in other receivables	0	32	186
Public offering costs in other receivables, net of amounts in accounts payable and accrued expenses	$ 0	$ 230	$ 0

Nature of Business	12 Months Ended
Nature of Business	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business References to Agios Throughout this Annual Report on Form 10-K, “we,” “us,” and “our,” and similar expressions, except where the context requires otherwise, refer to Agios Pharmaceuticals, Inc. and its consolidated subsidiaries, and “our board of directors” refers to the board of directors of Agios Pharmaceuticals, Inc. Overview We are a biopharmaceutical company committed to the fundamental transformation of patients’ lives through scientific leadership in the field of cellular metabolism, with the goal of making transformative, first- or best-in-class medicines. Our therapeutic areas of focus are cancer and rare genetic diseases, or RGDs, which are diseases that are directly caused by changes in genes or chromosomes, often passed from one generation to the next. Most RGDs are often associated with severe or life-threatening features. The incidence of a single RGD can vary widely but is generally very infrequent, usually equal to or less than one per 100,000 births. In both areas of cancer and RGDs, we are seeking to unlock the biology of cellular metabolism as a platform to create transformative therapies. We are located in Cambridge, Massachusetts. Our first commercial cancer product is IDHIFA®. In August 2017, the U.S. Food and Drug Administration, or FDA, granted our collaboration partner Celgene Corporation, or Celgene, approval of IDHIFA® for the treatment of adult patients with relapsed or refractory acute myeloid leukemia, or R/R AML, and an isocitrate dehydrogenase 2, or IDH2, mutation as detected by an FDA-approved test. IDHIFA®, an oral targeted inhibitor of the mutated IDH2 enzyme, is the first and only FDA-approved therapy for patients with R/R AML and an IDH2 mutation. Our most advanced clinical cancer product candidates are ivosidenib, which targets mutated isocitrate dehydrogenase 1, or IDH1, and AG-881, which is a brain-penetrant pan-IDH mutant inhibitor. These mutations are found in a wide range of hematological malignancies and solid tumors. In December 2017, we submitted a new drug application, or NDA, to the FDA for ivosidenib for the treatment of patients with R/R AML and an IDH1 mutation. We plan to submit an Marketing Authorization Application, or MAA, to the European Medicines Agency, or EMA, for ivosidenib for IDH1 mutant-positive R/R AML in the fourth quarter of 2018. Our next most advanced cancer product candidate is AG-270, an inhibitor of methionine adenosyltransferase 2a, or MAT2A. We submitted an investigational new drug application, or IND, for AG-270 in November 2017, and in December 2017 the FDA concluded that we may proceed with our planned phase 1 dose-escalation trial of AG-270 in multiple tumor types carrying a methylthioadenosine phosphorylase, or MTAP, deletion. Our most advanced preclinical cancer product candidate is an inhibitor of the metabolic enzyme dihydroorotate dehydrogenase, or DHODH. We plan to submit an IND for our DHODH inhibitor for the treatment of hematologic malignancies in the fourth quarter of 2018. The lead product candidate in our RGD program, AG-348, targets pyruvate kinase-R for the treatment of pyruvate kinase, or PK, deficiency. PK deficiency is a rare genetic disorder that often results in severe hemolytic anemia, jaundice and lifelong conditions associated with chronic anemia and secondary complications due to inherited mutations in the pyruvate kinase enzyme within red blood cells, or RBCs. We intend to initiate two global, pivotal trials of AG-348 in PK deficiency in the first half of 2018: ACTIVATE-T, a single arm trial of approximately 20 regularly transfused patients, is expected to initiate in the first quarter of 2018, and ACTIVATE, a 1:1 randomized, placebo-controlled trial of approximately 80 patients who do not receive regular transfusions, is expected to initiate in the second quarter of 2018. We also expect to initiate a phase 2 proof of concept trial of AG-348 in thalassemia in the fourth quarter of 2018. In addition to the aforementioned development programs, we are seeking to advance a number of early-stage discovery programs in the areas of cancer metabolism, RGDs and metabolic immuno-oncology, or MIO, a developing field which aims to modulate the activity of relevant immune cells by targeting critical metabolic nodes, thereby, enhancing the immune mediated anti-tumor response. 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 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. In January 2018, we completed a public offering of 7,089,553 shares of common at an offering price of $67.00 per share. We received net proceeds from this offering of $448.9 million, after deducting underwriting discounts and commissions paid by us. In addition, we granted the underwriters the right to purchase up to an additional 1,063,433 shares of common stock, which was exercised in January 2018, resulting in additional net proceeds to us of $67.3 million, after underwriting discounts and commissions. After giving effect to the full exercise of the over-allotment option, the number of shares sold by us in the public offering totaled 8,152,986 shares, and net proceeds to us totaled $516.2 million, after underwriting discounts and commissions. As of December 31, 2017, we had cash, cash equivalents and marketable securities of $567.8 million. Although we have incurred recurring losses and expect to continue to incur losses for the foreseeable future, we expect our cash, cash equivalents and marketable securities to be sufficient to fund current operations for at least the next twelve months from the issuance of the financial statements.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Principles of consolidation

The consolidated financial statements include our accounts and the accounts of our wholly owned subsidiaries, Agios Securities Corporation, Agios International Sarl, and Agios Limited. All intercompany transactions have been eliminated in consolidation. The consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles, or U.S. GAAP.

Use of estimates

The preparation of financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. Actual results could differ from those estimates.

Cash and cash equivalents

We consider highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are stated at fair value.

Marketable securities

Marketable securities at December 31, 2017 and 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 consolidated statements of comprehensive loss, until realized. Realized gains and losses are included in investment income on a specific-identification basis.

At December 31, 2017 and 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 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.

Concentrations of credit risk

Financial instruments which potentially subject us to credit risk consist primarily of cash, cash equivalents, and marketable securities. We hold these investments in highly rated financial institutions, and, by policy, limit the amounts of credit exposure to any one financial institution. These amounts at times may exceed federally insured limits. We have not experienced any credit losses in such accounts and do not believe we are exposed to any significant credit risk on these funds. We have no off-balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts, or other hedging arrangements.

We are also subject to credit risk on our collaboration and royalty receivables from Celgene. We have evaluated the creditworthiness of Celgene and determined it to be credit worthy. To date we have not experienced any losses with respect to our receivables.

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, either 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.

Our financial assets, which include cash equivalents and marketable securities, have been initially valued at the transaction price, and subsequently revalued at the end of each reporting period, utilizing third-party pricing services or other observable market 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 December 31, 2017 or 2016.

There have been no changes to the valuation methods during the years ended December 31, 2017 and 2016. We evaluate transfers between levels at the end of each reporting period.

The carrying amounts of collaboration receivable – related party, royalty receivable – related party, tenant improvement and other receivables, prepaid expenses and other current assets, accounts payable, and accrued expenses approximate their fair values due to their short-term maturities.

Collaboration, royalty and other receivables

Collaboration receivable – related party and royalty receivable – related party represent amounts due under the terms of our collaboration agreements with Celgene for reimbursements of certain costs and royalty on sales of IDHIFA®, respectively.

Based on our evaluation of credit worthiness, historical payment patterns, and general economic conditions, we did not record any allowance for doubtful accounts as of December 31, 2017 and 2016.

Property and equipment

Property and equipment consist of laboratory equipment, computer equipment and software, leasehold improvements, furniture and fixtures, and office equipment. Property and equipment is stated at cost, and depreciated using the straight-line method over the estimated useful lives of the respective assets:



Laboratory equipment	5 years
Computer equipment and software	3 years
Leasehold improvements	Shorter of asset’s useful life or remaining term of lease
Furniture and fixtures	5 years
Office equipment	5 years

Costs of major additions and betterments are capitalized; maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to expense as incurred. Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and the resulting gain or loss is recognized.

Impairment of long-lived assets

We periodically evaluate our long-lived assets for potential impairment in accordance with ASC 360, Property, Plant and Equipment. Potential impairment is assessed when there is evidence that events or changes in circumstances indicate that the carrying amount of an asset may not be recovered. Recoverability of these assets is assessed based on the undiscounted expected future cash flows from the assets, considering a number of factors, including past operating results, budgets and economic projections, market trends and product development cycles. If impairments are identified, assets are written down to their estimated fair value. We did not recognize any impairment charges through December 31, 2017.

Revenue recognition

We recognize revenue in accordance with the Financial Accounting Standards Board’s, or FASB, Accounting Standards Codification, or ASC, 605, Revenue Recognition. Accordingly, revenue is recognized for each unit of accounting when all of the following criteria are met:


•	persuasive evidence of an arrangement exists;


•	delivery has occurred or services have been rendered;


•	the seller’s price to the buyer is fixed or determinable; and


•	collectability is reasonably assured.

Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified current and amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as non-current.

Collaboration agreements with Celgene

To date, our revenue has primarily been generated from our collaboration agreements with Celgene. Celgene is a related party through ownership of our common stock. In April 2010, we entered into a collaboration agreement with Celgene focused on cancer metabolism, or the 2010 Agreement. The 2010 Agreement was amended in October 2011 and July 2014. 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's wholly owned subsidiary, 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.

Collaboration and license revenue

We account for the collaboration agreements with Celgene under ASC 605-25, Revenue Recognition - Multiple-Element Arrangements, or ASC 605-25. Pursuant to ASC 605-25, revenue arrangements where multiple products or services are sold together are evaluated to determine if each deliverable represents a separate unit of accounting based on the following criteria:


•	delivered item or items have value to the customer on a standalone basis, and


•	if the arrangement includes a general right of return relative to the delivered item or items, delivery or performance of the undelivered item or items is considered probable and substantially in the control of the vendor.

If a deliverable meets both criteria above, it is considered a separate unit of accounting. If a deliverable does not meet both criteria above, it will be evaluated in combination with other deliverables and, if appropriate, aggregated to form one unit of accounting. The arrangement consideration is then allocated to each unit of accounting based on the relative selling price, using our best estimate of selling price, or BESP, of each unit of accounting, if vendor specific objective evidence or third party evidence is not available. The provisions of ASC 605-25 are then applied to each unit of accounting to determine the appropriate revenue recognition.

We recognize revenue for the units of accounting over the term of the related contract or as undelivered items are delivered (proportional performance method), as appropriate. Under the proportional performance method, the consideration allocated to each unit of accounting is recognized as revenue based on the ratio of the level of effort incurred to date compared to the total estimated level of effort required to complete our performance obligations under the unit of accounting. Determining the total estimated level of effort required to complete all performance obligations requires judgment and estimation, including assumptions regarding future operating performance, the timelines of the clinical trial approvals and the estimated patient populations.

Reimbursement of research and development costs under our collaboration agreements with Celgene are recognized as revenue, provided that we are acting as the principal in the transaction according to the provisions outlined in ASC 605-45, Revenue Recognition – Principal Agent Considerations, the amounts are determinable, and collection of the related receivable is reasonably assured.

Milestone revenue

We apply the provisions of ASC 605-28, Revenue Recognition – Milestone Method, or ASC 605-28, pursuant to which we recognize revenue contingent upon the achievement of a milestone in its entirety in the period in which the milestone is achieved, only if the milestone meets all the criteria within the guidance to be considered substantive. In accordance with ASC 605-28, at the inception of each arrangement that includes milestone payments, we evaluate each contingent payment on an individual basis to determine whether they are considered substantive milestones, specifically reviewing factors such as the degree of certainty in achieving the milestone, the research and development risk and other risks that must be overcome to achieve the milestone, as well as the level of effort and investment required and whether the milestone consideration is reasonable relative to all deliverables and payment terms in the arrangement. This evaluation includes an assessment of whether (a) the consideration is commensurate with either (1) our performance to achieve the milestone, or (2) the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from our performance to achieve the milestone, (b) the consideration relates solely to past performance, and (c) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement.

Revenue from milestones, if they are nonrefundable and deemed substantive, are recognized upon achievement of the milestones. We recognize revenue associated with non-substantive milestones upon achievement of the milestone if there are no undelivered elements and we have no remaining performance obligations.

Research and development costs

Research and development costs are expensed as incurred. These costs include salaries and personnel-related costs, consulting fees, fees paid for contract research services, fees paid to clinical research organizations and other third parties associated with clinical trials, the costs of laboratory equipment and facilities, and other external costs.

Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.

Stock-based compensation

We account for stock-based compensation awards in accordance with ASC 718, Compensation –Stock Compensation, or ASC 718. For stock-based awards granted to employees and to members of the board of directors for their services and for participation in employee stock purchase plan, we estimate the grant date fair value of each option award using the Black-Scholes option-pricing model. The use of the Black-Scholes option-pricing model requires us to make assumptions with respect to the expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk-free interest rates and expected dividend yields of the common stock. For awards subject to service-based vesting conditions, we recognize stock-based compensation expense equal to the grant date fair value of stock options on a straight-line basis over the requisite service period. For awards subject to both performance and service-based vesting conditions, we recognize stock-based compensation expense over the remaining service period if the performance condition is considered probable of achievement using management’s best estimates.

In 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, including income tax consequences, classification of awards as either equity or liabilities, and classification in the statement of cash flows. The following summarizes the effects of the adoption on our consolidated financial statements:

•

Income taxes – Upon adoption of this standard, all excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the statement of operations. The tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We did not recognize any discrete adjustments to income tax expense for the year ended December 31, 2017, as we are in a full valuation allowance position. We applied the modified retrospective adoption approach beginning in 2017. This cumulative-effect adjustment related to tax assets that had previously arisen from tax deductions for stock-based compensation expenses that were greater than the compensation recognized for financial reporting. These assets had been excluded from the deferred tax assets and liabilities totals on the balance sheet as a result of certain realization requirements previously included in ASC 718. We recorded a cumulative-effect adjustment of approximately $32.7 million through retained earnings and deferred tax assets; however, due to the full valuation allowance, the only impact of the retrospective adoption is on disclosures presented in Note 11, Income Taxes.

•

Forfeitures – Upon adoption of ASU 2016-09, entities may also elect to estimate forfeitures and adjust the estimate when it is likely to change, which is consistent with pre-ASU 2016-09 guidance, or account for forfeitures as they occur. Beginning in January 1, 2017, we elected to account for forfeitures as they occur. The ASU is applied on a prospective basis, and prior periods have not been adjusted to reflect this change in accounting policy. The cumulative effect of the change in forfeiture policy in prior periods did not have a material impact on our statement of operations or balance sheet.

Upon adoption, no other aspects of ASU 2016-09 had a material effect on our consolidated financial statements or related footnote disclosures.

Income taxes

Income taxes are recorded in accordance with ASC 740, Accounting for Income Taxes, or ASC 740, which provides for deferred taxes using an asset and liability approach. We recognize deferred tax assets and liabilities for the expected future tax consequences of events that have been included in our financial statements or tax returns. We determine our deferred tax assets and liabilities based on differences between the financial reporting and tax bases of assets and liabilities, which are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Valuation allowances are provided, if based upon the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

We also account for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, we recognize the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances.

Comprehensive income (loss)

Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions, and other events and circumstances from non-owner sources, and currently consists of net loss and unrealized gains and losses on available-for-sale securities. Accumulated other comprehensive loss consists entirely of unrealized gains and losses from available-for-sale securities as of December 31, 2017 and 2016.

Net loss per share

Basic net loss per share is calculated by dividing net loss by the weighted-average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting weighted-average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock method. For purposes of the dilutive net loss per share calculation, stock options, including performance-based stock options which were determined to be probable of achievement, restricted stock units, unvested restricted stock and employee stock purchase plan shares are considered to be common stock equivalents but are excluded from the calculation of diluted net loss per share as their effect would be anti-dilutive.

Segment and geographic information

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision-making group, in making decisions on how to allocate resources and assess performance. Our chief operating decision maker is the chief executive officer. Our chief operating decision maker and we view our operations and manage our business as one operating segment.

Recent accounting pronouncements

Revenue from Contracts with Customers

In May 2014, the 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; 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 Securities and Exchange Commission, or SEC, staff; and ASU No. 2017-14, Income Statement—Reporting Comprehensive Income (Topic 220), Revenue Recognition (Topic 605), and Revenue from Contracts with Customers (Topic 606) (SEC Update), which adds ASC 606-10-S25-1 as a result of SEC Release 33-10403, 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 adopted the new standard effective January 1, 2018 under the modified retrospective method. During the fourth quarter of 2017, we substantially completed our assessment over the impact that this new standard will have on our consolidated balance sheets. We preliminarily expect to recognize an adjustment of approximately $30.0 million as a reduction of deferred revenue – related party with an offset to accumulated deficit on January 1, 2018 to reflect the cumulative effect of the accounting changes made upon the adoption of the standard. The finalization of our assessment may result in significant changes to our estimates that may materially impact our preliminary estimate of the cumulative effect.

Our collaboration agreements with Celgene, which are discussed in further detail within Note 8, Collaboration Agreements, are 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 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 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. In January 2018, the FASB issued ASU 2018-01, Leases (Topic 842), or ASU 2018-01, which adds two practical expedients to the the new lease guidance. Topic 842 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.

Subsequent events

We considered events or transactions occurring after the balance sheet date, but prior to the issuance of the consolidated financial statements, for potential recognition or disclosure in our consolidated financial statements. All significant subsequent events have been properly disclosed in the consolidated financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2017 (in thousands):



	Level 1		Level 2		Level 3		Total
Cash equivalents	$	33,831	$	54,916	$	—	$	88,747
Marketable securities:
Certificates of deposit	—		9,022		—		9,022
U.S. Treasuries	—		149,587		—		149,587
Government securities	—		68,174		—		68,174
Corporate debt securities	—		238,243		—		238,243
	$	33,831	$	519,942	$	—	$	553,773

The fair value of Level 2 instruments were determined through third-party pricing services. For a description of our validation procedures related to prices provided by third-party pricing services, refer to Note 2, Summary of Significant Accounting Policies, to these consolidated financial statements. There have been no changes to the valuation methods during the years ended December 31, 2017 and 2016.

Due to the lack of an active market, we transferred $149.6 million of U.S. Treasuries and $42.6 million of government securities from Level 1 to Level 2 during the year ended December 31, 2017. Also due to the lack of an active market, we transferred $11.0 million of government securities from Level 1 to Level 2 during the year ended December 31, 2016. We had no financial assets or liabilities that were classified as Level 3 at any point during the years ended December 31, 2017 and 2016.

- 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

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities at December 31, 2017 consisted of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	8,081	$	—	$	(11	)	$	8,070
U.S. Treasuries	113,852		—		(119		)	113,733
Government securities	44,421		—		(57		)	44,364
Corporate debt securities	155,222		—		(177		)	155,045
Non-current:
Certificates of deposit	960		—		(8		)	952
U.S. Treasuries	36,165		—		(311		)	35,854
Government securities	23,992		—		(182		)	23,810
Corporate debt securities	83,722		—		(524		)	83,198
	$	466,415	$	—	$	(1,389	)	$	465,026

Marketable securities at December 31, 2016 consisted 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

There were no material realized gains or losses on marketable securities for the years ended December 31, 2017 and 2016.

At December 31, 2017 and 2016, we held 240 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 December 31, 2017 and 2016 was $439.4 million and $335.4 million, respectively. There were no individual securities that were in a significant unrealized loss position as of December 31, 2017 and 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 December 31, 2017 and 2016.

Property and Equipment, net

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property and Equipment, net

Property and equipment, net consists of the following (in thousands):



	December 31,
	2017			2016
Laboratory equipment	$	17,524		$	14,529
Computer equipment and software	4,293			3,204
Leasehold improvements	20,322			19,858
Furniture and fixtures	752			748
Office equipment	319			233
Construction in progress	618			137
Total property and equipment	43,828			38,709
Less: accumulated depreciation	(19,397		)	(13,372		)
Total property and equipment, net	$	24,431		$	25,337

Depreciation expense for the years ended December 31, 2017, 2016 and 2015 was $6.4 million, $5.7 million and $3.3 million, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses and other current liabilities consist of the following (in thousands):



	December 31,
	2017		2016
Accrued compensation	$	15,693	$	11,092
Accrued research and development costs	14,849		20,266
Accrued professional fees	3,140		476
Accrued other	349		168
Total accrued expenses	$	34,031	$	32,002

Commitments and Contingent Liabilities

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingent Liabilities

Leases

We rent laboratory and office space under non-cancelable operating leases. These lease agreements contain various clauses for renewal at our option and escalation clauses. Rental expense under these leases, net of tenant improvement reimbursements, amounted to $6.0 million, $6.0 million and $7.1 million for the years ended December 31, 2017, 2016 and 2015, respectively.

We provided our landlord a standby letter of credit of $2.9 million as security for our leases. We are not required to maintain any cash collateral for the standby letter of credit.

As of December 31, 2017, minimum rental commitments under non-cancelable leases, for each of the next five years and total thereafter were as follows (in thousands):



2018	$	11,295
2019	11,770
2020	12,077
2021	12,392
2022	14,447
Thereafter	33,891
	$	95,872

In addition to rent, the leases may require us to pay additional amounts for taxes, insurance, maintenance and other operating expenses.

Program license agreements

We have entered into various cancelable license agreements for certain technology. None of our lead product candidates utilize technology covered by these licenses. Under the terms of these license agreements, we could be required to make clinical development, regulatory and sales-based milestone payments of up to $1.6 million, $5.4 million and $3.7 million, respectively, to the licensors.

The license agreements also require us to remit royalties in amounts ranging from 0.5% to 2.5% based on net sales of products utilizing the licensed technology. We are also required to make payments in amounts ranging from 7.0% to 25.0% for non-royalty income received from any sublicense of the rights granted to us under the agreements.

Milestone payment agreements

We entered into an agreement with a service provider to receive discounted upfront labor costs for a defined program in consideration of a milestone payment in five years from the effective date, as defined in the agreement. During the year ended December 31, 2016, we accrued a milestone payment of $4.1 million, which was paid during the year ended December 31, 2017. No other amounts are due to the service provider under the terms of the agreement.

Legal contingencies

From time to time, we may be involved in disputes and legal proceedings in the ordinary course of business. These proceedings may include allegations of infringement of intellectual property, employment or other matters. We do not have any ongoing legal proceedings that, based on our estimates, could have a material effect on our consolidated financial statements.

Collaboration Agreements

12 Months Ended

Dec. 31, 2017

Revenue Recognition and Deferred Revenue [Abstract]

Collaboration Agreements

2016 Agreement

In May 2016, we entered into the 2016 Agreement with Celgene, which is 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, our MAT2A inhibitor, will be governed by the 2016 Agreement.

During the research term of the 2016 Agreement, we plan to conduct research programs focused on discovering compounds that are active against metabolic targets in the immuno-oncology, or IO, field. The initial four-year research term will expire on May 17, 2020, and may be extended for up to two, or in specified cases, up to four additional one-year terms.

For each program under the 2016 Agreement, we may nominate compounds that meet specified criteria as development candidates and, in limited circumstances, Celgene may also nominate compounds as development candidates for each such program. Celgene may designate the applicable program for further development following any such nomination, after which we may conduct, at our expense, additional preclinical and clinical development for such program through the completion of an initial phase 1 dose escalation study.

At the end of the research term, Celgene may designate for continued development up to three research programs for which development candidates have yet to be nominated, which are referred to as continuation programs. We may conduct further research and preclinical and clinical development activities on any continuation program, at our expense, through the completion of an initial phase 1 dose escalation study.

We granted Celgene the right to obtain exclusive options for development and commercialization rights for each program that Celgene has designated for further development and for each continuation program. Celgene may exercise each such option beginning on the designation of a development candidate for such program (or on the designation of such program as a continuation program) and ending on the earlier of: (i) the end of a specified period after we have furnished Celgene with specified information about the initial phase 1 dose escalation study for such program, or (ii) January 1, 2030. Research programs that have applications in the inflammation or autoimmune, or I&I, field that may result from the 2016 Agreement will also be subject to the exclusive options described above.

We will retain rights to any program that Celgene does not designate for further development or as to which it does not exercise its option.

Under the terms of the 2016 Agreement, following Celgene’s exercise of its option with respect to a program, the parties will enter into either a co-development and co-commercialization agreement if such program is in the IO field, or a license agreement if such program is in the I&I field. Under each co-development and co-commercialization agreement, the two parties will co-develop and co-commercialize licensed products worldwide. Either we or Celgene will lead development and commercialization of licensed products for the United States, and Celgene will lead development and commercialization of licensed products outside of the United States. Depending on the country, the parties will each have the right to provide a portion of field-based marketing activities. Under each license agreement, Celgene will have the sole right to develop and commercialize licensed products worldwide.

Co-development and co-commercialization agreements

Under each co-development and co-commercialization agreement entered into under the 2016 Agreement, the parties will split all post-option exercise worldwide development costs, subject to specified exceptions, as well as any profits from any net sales of, or commercialization losses related to, licensed products in the IO field. Celgene has the option to designate one program in the IO field as the 65/35 program, for which Celgene will be the lead party for the United States and will have a 65% profit or loss share. For programs in the IO field other than the 65/35 program, we and Celgene will alternate, on a program-by-program basis, being the lead party for the United States, with us having the right to be the lead party for the first such program, and each party will have a 50% profit or loss share. The lead party for the United States will book commercial sales of licensed products, if any, in the United States, and Celgene will book commercial sales of licensed products, if any, outside of the United States.

License agreements

Under each license agreement under the 2016 Agreement, Celgene will be responsible for all post-option exercise worldwide development and associated costs, subject to specified exceptions, as well as worldwide commercialization and associated costs, for licensed products in the I&I field.

Financial terms

Under the terms of the 2016 Agreement, we received an initial upfront payment in the amount of $200.0 million. The 2016 Agreement provides specified rights to extend the research term for up to two, or in specified cases, up to four, additional years by paying a $40.0 million per-year extension fee. Celgene will pay an $8.0 million designation fee for each program that Celgene designates for further development and for each continuation program. During the year ended December 31, 2017, we received $8.0 million from Celgene upon the designation of AG-270, our MAT2A inhibitor, 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, of the applicable licensed products.

Opt-out right

Under the 2016 Agreement, we may elect to opt out of the cost and profit share under any co-development and co-commercialization agreement, subject to specified exceptions. Upon opting out, Celgene will have the sole right to develop, manufacture and commercialize the applicable licensed products throughout the world, at its cost, and we will undertake transitional activities reasonably necessary to transfer the development, manufacture and commercialization of such licensed products to Celgene, at our expense. Further, in lieu of the profit or loss sharing described above, we would be eligible to receive royalties at tiered, low double-digit percentage rates on Celgene’s net sales, if any, of the applicable licensed products. However, we would continue to be eligible to receive the developmental and regulatory milestone-based payments described above.

Term

The term of the 2016 Agreement commenced on May 17, 2016 and, if not terminated earlier, will expire upon the later of the last-to-expire of the research term and all option exercise periods, or, if an option is exercised by Celgene for one or more programs in the collaboration, upon the termination or expiration of the last-to-exist co-development and co-commercialization agreement or license agreement, as applicable, for any such program.

Termination

Subject to specified exceptions, Celgene may terminate the 2016 Agreement in its entirety for any reason by providing us with prior written notice if there are no active co-development and co-commercialization agreements or license agreements in place or on a program-by-program basis if there are no active co-development and co-commercialization agreements or license agreements in place for the terminated program(s). Either party may terminate the 2016 Agreement for the insolvency of the other party. On a program-by-program basis, prior to the exercise of an option, either party may terminate the 2016 Agreement either in its entirety or with respect to one or more programs on prior written notice to the other party in the case of an uncured material breach by the other party that frustrates the fundamental purpose of the 2016 Agreement. Following the exercise of an option for a program, either party may terminate the 2016 Agreement with respect to such program if such party terminates the co-development and co-commercialization agreement or license agreement for such program for an uncured material breach by the other party that frustrates the fundamental purpose of such agreement. Either party may terminate a co-development and co-commercialization agreement or a license agreement upon the bankruptcy or insolvency of the other party. Either party also has the right to terminate the co-development and co-commercialization agreement or license agreement if the other party or any of its affiliates challenges the validity, scope or enforceability of or otherwise opposes, any patent included within the intellectual property rights licensed to the other party under such agreement.

Exclusivity

While any of Celgene’s options remain available under the 2016 Agreement, subject to specified exceptions, we may not directly or indirectly develop, manufacture or commercialize, outside of the 2016 Agreement, any therapeutic modality in the IO or I&I field with specified activity against a metabolic target.

During the term of each co-development and co-commercialization agreement and license agreement, subject to specified exceptions, neither we nor Celgene may directly or indirectly develop, manufacture or commercialize outside of such agreement any therapeutic modality in any field with specified activity against the metabolic target that is the focus of the program licensed under such agreement.

Ivosidenib Letter Agreement

On May 17, 2016, we entered into a letter agreement with Celgene regarding ivosidenib, or the Ivosidenib Letter Agreement. Under the Ivosidenib Letter Agreement, the parties agreed 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. 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 Ivosidenib Letter Agreement, 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 Ivosidenib Letter Agreement, the parties also agreed to conduct specified transitional activities in connection with the termination. In addition, pursuant to the Ivosidenib Letter Agreement, the parties are released from their exclusivity obligations under the 2010 Agreement with respect to the IDH1 program. The Ivosidenib Letter Agreement does not affect the AG-881 Agreements, which are directed to both the IDH1 target and the 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. 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 the first 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.

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 year ended December 31, 2017, we earned $1.9 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, we identified the remaining deliverables under the modified arrangement, and determined the 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
July 2014 modification
Ivosidenib program license (1)		$21.2	million	1	Principal	Upon delivery of the licenses to Celgene, which occurred in January 2015
On-going development services (2) (3)		$50.8	million	5	Principal	Proportionally as services are delivered over the performance period, expected to be through June 2016
On-going research and development (2)		$13.6	million	1	Principal	Ratably over the performance period, expected to be through June 2016
Committee participations (4)		$0.2	million	1	Principal	Ratably over the performance period, expected to be through June 2016
April 2015 modification (supplants undelivered elements of July 2014 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 years ended December 31, 2017, 2016 and 2015, we recognized as collaboration revenue the following non-contingent consideration allocated to each undelivered element (in thousands):



	Years Ended December 31,
Undelivered Element	2017		2016		2015
July 2014 modification
Ivosidenib program license	$	—	$	—	$	15,808
On-going development services (principal)	—		—		14,711
On-going research and development	—		—		4,992
Committee participations	—		—		80
April 2015 modification
AG-881 program licenses	—		1,356		11,968
On-going development services (principal)	—		1,656		1,719
On-going research and development	—		4,584		7,644
Committee participations	—		89		121
May 2016 modification
On-going development services (principal)	11,827		21,308		—
On-going research and development	26,126		14,445		—
Committee participations	167		92		—
Total collaboration revenue - related party		$38,120		$43,530		$57,043

During the years ended December 31, 2017, 2016 and 2015, we recognized as a reduction of research and development expenses the following non-contingent consideration allocated to each undelivered element (in thousands):



	Modification Period	Years Ended December 31,
Undelivered Element	Modification Period	2017		2016		2015
On-going development services (agent)	April 2015	$	—	$	7,456	$	17,122
On-going development services (agent)	May 2016	7,797		5,662		—
Total reduction of research and development expenses			$7,797		$13,118		$17,122

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 years ended December 31, 2017, 2016 and 2015, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):



	Years Ended December 31,
	2017		2016		2015
Collaboration revenue - related party
Development activities	$	—	$	1,192	$	2,076
Commercial activities	2,954		170		—
Reduction of research and development expenses
Development activities	14		6,596		8,051

For the years ended December 31, 2017, 2016 and 2015, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):



	Years Ended December 31,
	2017		2016		2015
Collaboration revenue - related party	$	41,074	$	44,892	$	59,119
Reduction of research and development expenses	7,811		19,714		25,173

As of December 31, 2017 and December 31, 2016, we recorded a collaboration receivable – related party of $2.4 million and $4.9 million, respectively, related to reimbursable development costs.

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 collaboration revenue during the three months ended March 31, 2016. No milestones were earned during the years ended December 31, 2017 and 2015. The next potential milestone expected to be achieved under our collaboration agreements with Celgene is the filing of a first NDA in a country other than the U.S. Achievement of this event will result in milestone payments of $15.0 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 DHODH, or the Aurigene Agreement.

Under the terms of the Aurigene Agreement, Aurigene will provide us exclusive rights to its portfolio of novel small molecules for DHODH. Financial terms of the Aurigene Agreement include a $3.0 million upfront payment and potential future milestone payments of up to $17.0 million if we achieve certain development and regulatory milestones. The next potential milestone expected to be achieved under our collaboration agreements with Aurigene is the initiation of the first phase 1 clinical trial for DHODH. Achievement of this event will result in milestone payments owed to Aurigene of $2.0 million.

Aurigene is also eligible to receive low single-digit royalties on net product sales, if any. We will conduct preclinical studies and, if successful, fund further global research and development, as well as regulatory and commercial activities.

The term of the Aurigene Agreement will continue until the earlier of: (a) termination for convenience at our sole discretion upon 90 days prior written notice, (b) termination by either party for material breach, or (c) the expiration of the last-to-expire of all payment obligations hereunder with respect to all licensed products under the Aurigene Agreement.

Accounting analysis

The $3.0 million upfront payment was incurred in the year ended December 31, 2017 and recorded as research and development expense. Costs incurred and milestone payments due to Aurigene prior to regulatory approval are recognized as expenses in the period incurred. Payments due to Aurigene upon or subsequent to regulatory approval will be capitalized and amortized over the shorter of the remaining license or product patent life.

Common Stock	12 Months Ended
Common Stock	Dec. 31, 2017
Equity [Abstract]
Common Stock	Common Stock We are authorized to issue 125,000,000 shares of our common stock. Holders of common stock are entitled to one vote per share. Additionally, holders of common stock are entitled to receive dividends, if and when declared by our board of directors, and to share ratably in our assets legally available for distribution to our shareholders in the event of liquidation.

Share-Based Payments

12 Months Ended

Dec. 31, 2017

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

Share-Based Payments

Stock incentive plans

In June 2013, our Board of Directors adopted and, in July 2013 our stockholders approved, the 2013 Stock Incentive Plan, or the 2013 Plan. The 2013 Plan became effective upon the closing of our initial public offering and provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, or RSUs, performance-based stock units, or PSUs, and other stock-based awards. Following the adoption of the 2013 Plan, we granted no further stock options or other awards under the 2007 Stock Incentive Plan, or the 2007 Plan. Any options or awards outstanding under the 2007 Plan at the time of adoption of the 2013 Plan remain outstanding and effective. As of December 31, 2017, the total number of shares reserved under the 2007 Plan and the 2013 Plan are 7,206,938, and we had 1,327,606 shares available for future issuance under the 2013 Plan.

The 2013 Plan provides for an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2015 and continuing until the expiration of the 2013 Plan, equal to the lesser of (i) 2,000,000 shares of common stock, (ii) 4% of the outstanding shares of common stock on such date or (iii) an amount determined by our Board of Directors. On January 1, 2018, the annual increase for the 2013 Plan resulted in an additional 1,953,046 shares authorized for issuance.

Stock options

The following table summarizes the stock option activity of all stock incentive plans for the year ended December 31, 2017.



	Number of Stock Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	5,218,880		$	46.79	7.28	$	63,559
Granted	1,620,652		51.78
Exercised	(730,478	)	16.42
Forfeited/Expired	(531,492	)	74.48
Outstanding at December 31, 2017	5,577,562		$	49.58	7.27	$	94,336
Exercisable at December 31, 2017	2,936,068		$	44.32	5.98	$	74,229
Vested and expected to vest at December 31, 2017	5,577,562		$	49.58	7.27	$	94,336

The weighted-average grant date fair value of options granted was $35.24, $28.41 and $65.38 during the years ended December 31, 2017, 2016 and 2015, respectively. The total intrinsic value of options exercised was $31.5 million $26.4 million and $50.9 million during the years ended December 31, 2017, 2016 and 2015, respectively.

At December 31, 2017, the total unrecognized compensation expense related to unvested stock option awards was $85.3 million, which we expect to recognize over a weighted-average period of approximately 2.4 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 year ended December 31, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	77,050		$	49.60
Granted	66,334		52.23
Vested	(7,500	)	122.22
Forfeited	(10,300	)	39.76
Unvested shares at December 31, 2017	125,584		$	47.46

As of December 31, 2017, there was approximately $2.4 million of total unrecognized compensation expense related to RSUs, which we expect to be recognized over a weighted-average period of 1.2 years.

Performance-based stock options

During the years ended December 31, 2017, 2016 and 2015, 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 December 31, 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 December 31, 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 year ended December 31, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	200,613		$	53.36
Granted	18,667		52.75
Vested	—		—
Forfeited	(43,094	)	54.63
Unvested shares at December 31, 2017	176,186		$	52.98

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 December 31, 2017, there was approximately $9.3 million of total unrecognized compensation expense related to PSUs with performance-based vesting criteria that are not considered probable of achievement.

2013 Employee Stock Purchase Plan

In June 2013, our Board of Directors adopted, and in July 2013 our stockholders approved, the 2013 Employee Stock Purchase Plan, or the 2013 ESPP. 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, or IRS, limits. We issued 59,651 shares and 36,680 shares during the years ended December 31, 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 December 31, 2017, we had 213,791 shares available for future issuance under the 2013 ESPP.

Stock-based compensation expense

During the years ended December 31, 2017, 2016 and 2015, 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 consolidated statements of operations is as follows (in thousands):



	Years Ended December 31,
	2017		2016		2015
Stock options	$	43,997	$	39,305	$	30,331
Restricted stock units	2,858		1,964		902
Performance-based stock options	—		46		341
Employee Stock Purchase Plan	954		771		389
Total stock-based compensation expense	$	47,809	$	42,086	$	31,963

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



	Years Ended December 31,
	2017		2016		2015
Research and development expense	$	30,807	$	25,386	$	17,419
General and administrative expense	17,002		16,700		14,544
	$	47,809	$	42,086	$	31,963

No related tax benefits were recognized for the years ended December 31, 2017, 2016 and 2015.

The fair value of each stock option granted to employees is estimated on the date of grant using the Black-Scholes option-pricing model. For non-employees, the fair value of each stock option is estimated on each vesting and reporting date using the Black-Scholes option-pricing model. The following table summarizes the weighted average assumptions used in calculating the grant date fair value of the awards:



	Years Ending December 31,
	2017		2016		2015
Risk-free interest rate	2.05	%	1.42	%	1.71	%
Expected dividend yield	—		—		—
Expected term (in years)	6.05		6.05		6.04
Expected volatility	77.73	%	72.84	%	69.62	%

Expected term

We use the “simplified method” as prescribed by the Securities and Exchange Commission Staff Accounting Bulletin No. 107, Share Based Payments, to estimate the expected term of stock option grants. Under this approach, the weighted-average expected life is presumed to be the average of the contractual term of ten years and the weighted-average vesting term of the our stock options, taking into consideration multiple vesting tranches. We utilize this method due to lack of historical data and the plain-vanilla nature of our share-based awards.

Volatility

We use a weighted-average of expected volatility based on the volatilities of a representative group of publicly traded biopharmaceutical companies, including ourselves. The expected volatility has been determined using a weighted-average of the historical volatilities of the representative group of companies for a period equal to the expected term of the option grant.

Risk-free rate

The risk-free rate is based on the yield curve of U.S. Treasury securities with periods commensurate with the expected term of the options being valued.

Dividends

We have never paid, and do not anticipate paying, any cash dividends in the foreseeable future, and, therefore, use an expected dividend yield of zero in the option-pricing model.

Forfeitures

Upon adoption of ASU 2016-09, we elected to account for forfeitures as they occur and, therefore, do not estimate forfeitures.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

The domestic and foreign components of loss before income taxes are as follows (in thousands):



	Years Ended December 31,
	2017			2016			2015
Domestic	$	(290,423	)	$	(179,896	)	$	(111,057	)
Foreign	(24,247		)	(18,575		)	(6,674		)
Total	$	(314,670	)	$	(198,471	)	$	(117,731	)

We did not have any provision for income taxes for the years ended December 31, 2017, 2016 and 2015.

A reconciliation of the expected income tax benefit (expense) computed using the federal statutory income tax rate to our effective income tax rate is as follows for the years ended December 31, 2017, 2016 and 2015:



	Years Ended December 31,
	2017		2016		2015
Income tax benefit computed at federal statutory tax rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	4.0	%	2.9	%	4.5	%
Change in valuation allowance	(19.4	)%	(43.4	)%	(44.6	)%
General business credits and other credits	10.4	%	9.5	%	8.4	%
Permanent differences and other adjustments	—	%	(0.3	)%	(0.3	)%
Incentive stock options	0.3	%	(1.8	)%	(1.8	)%
Foreign rate differential	(1.6	)%	(1.9	)%	(1.2	)%
Impact of federal rate change	(28.7	)%	—	%	—	%
Total	—	%	—	%	—	%

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of our deferred tax assets and liabilities for the years ended December 31, 2017 and 2016 are as follows (in thousands):



	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	131,165		$	126,077
Deferred revenue	41,243			8,051
Tax credit carryforwards	100,791			43,350
Purchased intangible assets	3,906			4,410
Stock-based compensation	20,539			22,731
Deferred rent	5,042			8,516
Non-deductible accruals and reserves	3,778			3,310
Total deferred tax assets	306,464			216,445
Depreciation and amortization	$	(4,549	)	$	(8,412	)
Less: valuation allowance	(301,915		)	(208,033		)
Net deferred taxes	$	—		$	—

In December 2017, the Tax Cuts and Jobs Act, or TCJA, was signed into law. Among other things, the TCJA permanently lowers the corporate federal income tax rate to 21% from the existing maximum rate of 35%, effective for tax years including or commencing January 1, 2018. As a result of the reduction of the corporate federal income tax rate to 21%, U.S. GAAP requires companies to revalue their deferred tax assets and deferred tax liabilities as of the date of enactment, with the resulting tax effects accounted for in the reporting period of enactment. This revaluation resulted in a provision of $90.0 million to income tax expense in continuing operations and a corresponding reduction in the valuation allowance. As a result, there was no impact on our consolidated statements of operations from the reduction in tax rate. The other provisions of the TCJA did not have a material impact on the consolidated financial statements.

Our preliminary estimate of the TCJA and the remeasurement of our deferred tax assets and liabilities is subject to the finalization of management’s analysis related to certain matters, such as developing interpretations of the provisions of the TCJA, changes to certain estimates and the filing of our tax returns. U.S. Treasury regulations, administrative interpretations or court decisions interpreting the TJCA may require further adjustments and changes in our estimates.

The final determination of the TCJA and the remeasurement of our deferred assets and liabilities will be completed as additional information becomes available, but no later than one year from the enactment of the TCJA.

As of December 31, 2017, we had net operating loss carryforwards, or NOLs, available to reduce federal, state and foreign income taxes of approximately $454.6 million, $456.7 million and $46.2 million, respectively. If not utilized, these NOLs begin to expire in 2033, 2032 and 2022, respectively. At December 31, 2017, we also had available research and development tax credits for federal and state income tax purposes of approximately $18.5 million and $8.5 million, respectively. If not utilized, the credits begin to expire in 2027 and 2020 for federal and state income tax purposes, respectively. We engaged in clinical testing activities and incurred expenses that qualify for the federal orphan drug tax credit. At December 31, 2017, we had available orphan drug tax credits for federal purposes only of approximately $75.6 million. If not utilized, the orphan drug credits begin to expire in 2035.

We adopted ASU 2016-09 during the quarter ended March 31, 2017. As a result of the adoption, the net operating losses deferred tax assets increased by $32.7 million and were offset by a corresponding increase in the valuation allowance. The adoption of ASU 2016-09 had no impact on our consolidated balance sheets or consolidated statements of operations.

As provided by Section 382 of the Internal Revenue Code of 1986, or Section 382, and similar state provisions, utilization of NOLs and tax credit carryforwards may be subject to substantial annual limitations due to ownership change limitations that have previously occurred or that could occur in the future. Ownership changes may limit the amount of NOLs and tax credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of five percent stockholders in the stock of a corporation by more than 50 percent in the aggregate over a three year period. During the year ended December 31, 2017, we completed a Section 382 study to determine whether any ownership change has occurred since our formation and determined that transactions have resulted in two ownership changes, as defined by Section 382. The impact of the ownership changes has been reflected in our deferred tax assets in the table above. There could be additional ownership changes after December 31, 2017 that could further limit the amount of NOLs and tax credit carryforwards that we can utilize.

As required by ASC 740, we have evaluated the positive and negative evidence bearing upon the realizability of our deferred tax assets. Based on the weight of available evidence, both positive and negative, we recorded a valuation allowance of $301.9 million and $208.0 million as of December 31, 2017 and December 31, 2016, respectively, because we have determined that it is more likely than not that these assets will not be fully realized. The valuation allowance increased by $93.9 million, $86.1 million and $52.5 million for the years ended December 31, 2017, 2016 and 2015, respectively.

We apply the accounting guidance in ASC 740 related to accounting for uncertainty in income taxes. Our reserves related to taxes are based on a determination of whether, and how much of, a tax benefit taken by us in our tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit.

The following table presents our unrecognized tax benefits activity for the years ended December 31, 2017 and 2016 (in thousands):



	December 31,
	2017		2016
Unrecognized tax benefits at 12/31/2016	$	—	$	—
Gross increases - current period tax positions	11,263		—
Unrecognized tax benefits at 12/31/2017	11,263		—

The uncertain tax position does not impact our effective income tax rate due to the full valuation allowance.

We are subject to taxation in the United States and Switzerland. The statute of limitations for assessment by the IRS and state tax authorities is open for tax years ending December 31, 2017, 2016, 2015, and 2014, although carryforward attributes that were generated for tax years prior to 2014 may still be adjusted upon examination by the IRS or state tax authorities if they either have been, or will be, used in a future period. The statute of limitations for assessment in Switzerland remains open for tax year ending December 31, 2017, 2016, and 2015. There are currently no federal, state or foreign audits in progress.

Defined Contribution Benefit Plan	12 Months Ended
Defined Contribution Benefit Plan	Dec. 31, 2017
Retirement Benefits [Abstract]
Defined Contribution Benefit Plan	Defined Contribution Benefit Plan We sponsor a 401(k) retirement plan, in which substantially all of our full-time employees are eligible to participate. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. We will make matching contributions equal to 50% of the employee’s contributions, subject to a maximum of 6% of eligible compensation.

Net Loss per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss per Share

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 the years ended December 31, 2017, 2016 and 2015. Furthermore, 176,186 PSUs that were previously granted had not vested as of December 31, 2017 and were excluded from diluted shares outstanding as the vesting conditions for the awards, discussed further in Note 10, Share-Based Payments, had not been met as of December 31, 2017.

The following common stock equivalents were excluded from the calculation of diluted net loss per share applicable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:



	Years ended December 31,
	2017	2016	2015
Stock options	5,577,562	5,218,880	4,618,697
Restricted stock units	125,584	77,050	15,000
Unvested restricted stock	—	—	—
Employee stock purchase plan shares	22,062	24,018	7,721
	5,725,208	5,319,948	4,641,418

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2017 and 2016 (in thousands, except per share data):



2017	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	10,508		$	11,346		$	11,358		$	9,799
Loss from operations	(67,047		)	(84,600		)	(79,017		)	(90,130		)
Net loss	(66,166		)	(83,082		)	(77,137		)	(88,285		)
Net loss per share – basic and diluted	(1.56		)	(1.78		)	(1.59		)	(1.81		)

2016	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	31,281		$	6,978		$	8,985		$	22,648
Loss from operations	(23,594		)	(56,470		)	(63,512		)	(57,409		)
Net loss	(23,198		)	(55,953		)	(62,834		)	(56,486		)
Net loss per share – basic and diluted	(0.61		)	(1.47		)	(1.63		)	(1.34		)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Principles of consolidation

Use of estimates

Cash and cash equivalents

We consider highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are stated at fair value.

Marketable securities

Concentrations of credit risk

Fair value measurements

Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities.

There have been no changes to the valuation methods during the years ended December 31, 2017 and 2016. We evaluate transfers between levels at the end of each reporting period.

Collaboration, royalty and other receivables

Property and equipment



Laboratory equipment	5 years
Computer equipment and software	3 years
Leasehold improvements	Shorter of asset’s useful life or remaining term of lease
Furniture and fixtures	5 years
Office equipment	5 years

Impairment of long-lived assets

Revenue recognition


•	persuasive evidence of an arrangement exists;


•	delivery has occurred or services have been rendered;


•	the seller’s price to the buyer is fixed or determinable; and


•	collectability is reasonably assured.

Collaboration agreements with Celgene

Collaboration and license revenue


•	delivered item or items have value to the customer on a standalone basis, and


•	if the arrangement includes a general right of return relative to the delivered item or items, delivery or performance of the undelivered item or items is considered probable and substantially in the control of the vendor.

Milestone revenue

Research and development costs

Stock-based compensation

•

Upon adoption, no other aspects of ASU 2016-09 had a material effect on our consolidated financial statements or related footnote disclosures.

Income taxes

Comprehensive income (loss)

Net loss per share

Segment and geographic information

Recent accounting pronouncements

Revenue from Contracts with Customers

Other Recent Accounting Pronouncements

Subsequent events

Collaboration revenue

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Estimated Useful Lives of Property and Equipment

Property and equipment is stated at cost, and depreciated using the straight-line method over the estimated useful lives of the respective assets:



Laboratory equipment	5 years
Computer equipment and software	3 years
Leasehold improvements	Shorter of asset’s useful life or remaining term of lease
Furniture and fixtures	5 years
Office equipment	5 years

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

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

The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of December 31, 2017 (in thousands):



	Level 1		Level 2		Level 3		Total
Cash equivalents	$	33,831	$	54,916	$	—	$	88,747
Marketable securities:
Certificates of deposit	—		9,022		—		9,022
U.S. Treasuries	—		149,587		—		149,587
Government securities	—		68,174		—		68,174
Corporate debt securities	—		238,243		—		238,243
	$	33,831	$	519,942	$	—	$	553,773

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities

Marketable securities at December 31, 2017 consisted of the following (in thousands):



	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Current:
Certificates of deposit	$	8,081	$	—	$	(11	)	$	8,070
U.S. Treasuries	113,852		—		(119		)	113,733
Government securities	44,421		—		(57		)	44,364
Corporate debt securities	155,222		—		(177		)	155,045
Non-current:
Certificates of deposit	960		—		(8		)	952
U.S. Treasuries	36,165		—		(311		)	35,854
Government securities	23,992		—		(182		)	23,810
Corporate debt securities	83,722		—		(524		)	83,198
	$	466,415	$	—	$	(1,389	)	$	465,026

Marketable securities at December 31, 2016 consisted 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

Property and Equipment, net (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

Property and equipment, net consists of the following (in thousands):



	December 31,
	2017			2016
Laboratory equipment	$	17,524		$	14,529
Computer equipment and software	4,293			3,204
Leasehold improvements	20,322			19,858
Furniture and fixtures	752			748
Office equipment	319			233
Construction in progress	618			137
Total property and equipment	43,828			38,709
Less: accumulated depreciation	(19,397		)	(13,372		)
Total property and equipment, net	$	24,431		$	25,337

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Summary of Accrued Expenses

Accrued expenses and other current liabilities consist of the following (in thousands):



	December 31,
	2017		2016
Accrued compensation	$	15,693	$	11,092
Accrued research and development costs	14,849		20,266
Accrued professional fees	3,140		476
Accrued other	349		168
Total accrued expenses	$	34,031	$	32,002

Commitments and Contingent Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Summary of Future Annual Minimum Lease Payments Due Under Operating Leases

As of December 31, 2017, minimum rental commitments under non-cancelable leases, for each of the next five years and total thereafter were as follows (in thousands):



2018	$	11,295
2019	11,770
2020	12,077
2021	12,392
2022	14,447
Thereafter	33,891
	$	95,872

Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 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

For the years ended December 31, 2017, 2016 and 2015, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):



	Years Ended December 31,
	2017		2016		2015
Collaboration revenue - related party
Development activities	$	—	$	1,192	$	2,076
Commercial activities	2,954		170		—
Reduction of research and development expenses
Development activities	14		6,596		8,051



	Modification Period	Years Ended December 31,
Undelivered Element	Modification Period	2017		2016		2015
On-going development services (agent)	April 2015	$	—	$	7,456	$	17,122
On-going development services (agent)	May 2016	7,797		5,662		—
Total reduction of research and development expenses			$7,797		$13,118		$17,122

During the years ended December 31, 2017, 2016 and 2015, we recognized as collaboration revenue the following non-contingent consideration allocated to each undelivered element (in thousands):



	Years Ended December 31,
Undelivered Element	2017		2016		2015
July 2014 modification
Ivosidenib program license	$	—	$	—	$	15,808
On-going development services (principal)	—		—		14,711
On-going research and development	—		—		4,992
Committee participations	—		—		80
April 2015 modification
AG-881 program licenses	—		1,356		11,968
On-going development services (principal)	—		1,656		1,719
On-going research and development	—		4,584		7,644
Committee participations	—		89		121
May 2016 modification
On-going development services (principal)	11,827		21,308		—
On-going research and development	26,126		14,445		—
Committee participations	167		92		—
Total collaboration revenue - related party		$38,120		$43,530		$57,043

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
July 2014 modification
Ivosidenib program license (1)		$21.2	million	1	Principal	Upon delivery of the licenses to Celgene, which occurred in January 2015
On-going development services (2) (3)		$50.8	million	5	Principal	Proportionally as services are delivered over the performance period, expected to be through June 2016
On-going research and development (2)		$13.6	million	1	Principal	Ratably over the performance period, expected to be through June 2016
Committee participations (4)		$0.2	million	1	Principal	Ratably over the performance period, expected to be through June 2016
April 2015 modification (supplants undelivered elements of July 2014 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 years ended December 31, 2017, 2016 and 2015, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):



	Years Ended December 31,
	2017		2016		2015
Collaboration revenue - related party	$	41,074	$	44,892	$	59,119
Reduction of research and development expenses	7,811		19,714		25,173

Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2017

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

Summary of Company's Stock Option Activity of all Stock Incentive Plans

The following table summarizes the stock option activity of all stock incentive plans for the year ended December 31, 2017.



	Number of Stock Options		Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)	Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2016	5,218,880		$	46.79	7.28	$	63,559
Granted	1,620,652		51.78
Exercised	(730,478	)	16.42
Forfeited/Expired	(531,492	)	74.48
Outstanding at December 31, 2017	5,577,562		$	49.58	7.27	$	94,336
Exercisable at December 31, 2017	2,936,068		$	44.32	5.98	$	74,229
Vested and expected to vest at December 31, 2017	5,577,562		$	49.58	7.27	$	94,336

Unvested Stock Unit Activity

The following table presents RSU activity for the year ended December 31, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	77,050		$	49.60
Granted	66,334		52.23
Vested	(7,500	)	122.22
Forfeited	(10,300	)	39.76
Unvested shares at December 31, 2017	125,584		$	47.46

Schedule of Performance-Based Units

The following table presents PSU activity for the year ended December 31, 2017:



	Number of Stock Units		Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2016	200,613		$	53.36
Granted	18,667		52.75
Vested	—		—
Forfeited	(43,094	)	54.63
Unvested shares at December 31, 2017	176,186		$	52.98

Schedule of Stock-Based Compensation Expense by Award Type Included Within the Condensed Consolidated Statements of Operations

Stock-based compensation expense by award type included within the consolidated statements of operations is as follows (in thousands):



	Years Ended December 31,
	2017		2016		2015
Stock options	$	43,997	$	39,305	$	30,331
Restricted stock units	2,858		1,964		902
Performance-based stock options	—		46		341
Employee Stock Purchase Plan	954		771		389
Total stock-based compensation expense	$	47,809	$	42,086	$	31,963

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

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



	Years Ended December 31,
	2017		2016		2015
Research and development expense	$	30,807	$	25,386	$	17,419
General and administrative expense	17,002		16,700		14,544
	$	47,809	$	42,086	$	31,963

Schedule of Grant Date Fair Value Option Award Weighted Average Assumptions Used

The following table summarizes the weighted average assumptions used in calculating the grant date fair value of the awards:



	Years Ending December 31,
	2017		2016		2015
Risk-free interest rate	2.05	%	1.42	%	1.71	%
Expected dividend yield	—		—		—
Expected term (in years)	6.05		6.05		6.04
Expected volatility	77.73	%	72.84	%	69.62	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Loss Before Income Taxes

The domestic and foreign components of loss before income taxes are as follows (in thousands):



	Years Ended December 31,
	2017			2016			2015
Domestic	$	(290,423	)	$	(179,896	)	$	(111,057	)
Foreign	(24,247		)	(18,575		)	(6,674		)
Total	$	(314,670	)	$	(198,471	)	$	(117,731	)

Reconciliation of Expected Income Tax Benefit (Expense) Computed Using Federal Statutory Income Tax Rate



	Years Ended December 31,
	2017		2016		2015
Income tax benefit computed at federal statutory tax rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	4.0	%	2.9	%	4.5	%
Change in valuation allowance	(19.4	)%	(43.4	)%	(44.6	)%
General business credits and other credits	10.4	%	9.5	%	8.4	%
Permanent differences and other adjustments	—	%	(0.3	)%	(0.3	)%
Incentive stock options	0.3	%	(1.8	)%	(1.8	)%
Foreign rate differential	(1.6	)%	(1.9	)%	(1.2	)%
Impact of federal rate change	(28.7	)%	—	%	—	%
Total	—	%	—	%	—	%

Company's Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities for the years ended December 31, 2017 and 2016 are as follows (in thousands):



	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	131,165		$	126,077
Deferred revenue	41,243			8,051
Tax credit carryforwards	100,791			43,350
Purchased intangible assets	3,906			4,410
Stock-based compensation	20,539			22,731
Deferred rent	5,042			8,516
Non-deductible accruals and reserves	3,778			3,310
Total deferred tax assets	306,464			216,445
Depreciation and amortization	$	(4,549	)	$	(8,412	)
Less: valuation allowance	(301,915		)	(208,033		)
Net deferred taxes	$	—		$	—

Schedule of Unrecognized Tax Benefits Rollforward

The following table presents our unrecognized tax benefits activity for the years ended December 31, 2017 and 2016 (in thousands):



	December 31,
	2017		2016
Unrecognized tax benefits at 12/31/2016	$	—	$	—
Gross increases - current period tax positions	11,263		—
Unrecognized tax benefits at 12/31/2017	11,263		—

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Common Stock Excluded from Calculation of Diluted Earnings Per Share



	Years ended December 31,
	2017	2016	2015
Stock options	5,577,562	5,218,880	4,618,697
Restricted stock units	125,584	77,050	15,000
Unvested restricted stock	—	—	—
Employee stock purchase plan shares	22,062	24,018	7,721
	5,725,208	5,319,948	4,641,418

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Summary of Quarterly Financial Data

The following table contains quarterly financial information for 2017 and 2016 (in thousands, except per share data):



2017	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	10,508		$	11,346		$	11,358		$	9,799
Loss from operations	(67,047		)	(84,600		)	(79,017		)	(90,130		)
Net loss	(66,166		)	(83,082		)	(77,137		)	(88,285		)
Net loss per share – basic and diluted	(1.56		)	(1.78		)	(1.59		)	(1.81		)

2016	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Total revenue	$	31,281		$	6,978		$	8,985		$	22,648
Loss from operations	(23,594		)	(56,470		)	(63,512		)	(57,409		)
Net loss	(23,198		)	(55,953		)	(62,834		)	(56,486		)
Net loss per share – basic and diluted	(0.61		)	(1.47		)	(1.63		)	(1.34		)

Nature of Business - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Jan. 31, 2018	Apr. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)		5,808,080.00
Net proceeds from public offering		$ 270,200	$ 270,250	$ 162,150	$ 0
Cash, cash equivalents and marketable securities			$ 567,800
Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)		5,050,505
Offering price (in usd per share)		$ 49.50
Net proceeds from public offering		$ 235,000
Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)		757,575
Net proceeds from public offering		$ 35,200
Subsequent Event
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	8,152,986
Net proceeds from public offering	$ 516,200
Subsequent Event \| Public Offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	7,089,553
Offering price (in usd per share)	$ 67
Net proceeds from public offering	$ 448,900
Subsequent Event \| Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued from public offering (in shares)	1,063,433
Net proceeds from public offering	$ 67,300

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Jan. 01, 2018 USD ($)	Mar. 31, 2017 USD ($)
Schedule of Significant Accounting Policies [Line Items]
Minimum period to liquidate	12 months	12 months
Allowance for doubtful accounts	$ 0	$ 0
Adjustment to accumulated deficit	$ (798,061,000)	(483,151,000)
Number of operating segments \| segment	1
Adjustment to deferred revenue	$ 37,842,000	$ 35,913,000
Minimum
Schedule of Significant Accounting Policies [Line Items]
Investment maturity period, non-current	1 year	1 year
Maximum
Schedule of Significant Accounting Policies [Line Items]
Investment maturity period, current	1 year	1 year
Investment maturity period, non-current	2 years	2 years
ASU 2016-09
Schedule of Significant Accounting Policies [Line Items]
Deferred tax assets	$ 32,700,000			$ 32,700,000
Adjustment to accumulated deficit	$ 32,700,000
Scenario, Forecast \| ASU 2014-09
Schedule of Significant Accounting Policies [Line Items]
Adjustment to accumulated deficit			$ (30,000,000)
Adjustment to deferred revenue			$ (30,000,000)

Summary of Significant Accounting Policies - Estimated Useful Lives of Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2017
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Computer equipment and software
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	3 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	5 years
Office equipment
Property, Plant and Equipment [Line Items]
Estimated useful lives of property and equipment	5 years

Fair Value Measurements - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring $ in Thousands	Dec. 31, 2017 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 88,747
Total cash equivalents and marketable securities	553,773
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	9,022
U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	149,587
Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	68,174
Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	238,243
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	33,831
Total cash equivalents and marketable securities	33,831
Level 1 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 1 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	54,916
Total cash equivalents and marketable securities	519,942
Level 2 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	9,022
Level 2 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	149,587
Level 2 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	68,174
Level 2 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	238,243
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0
Total cash equivalents and marketable securities	0
Level 3 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	0
Level 3 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	$ 0

Fair Value Measurements - Additional Information (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets (liabilities)	$ 0	$ 0
Fair Value, Measurements, Recurring \| U.S. Treasuries \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers of assets from Level 1 to Level 2	149,600,000
Fair Value, Measurements, Recurring \| Government securities \| Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers of assets from Level 1 to Level 2	$ 42,600,000	$ 11,000,000

Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 8,081	$ 11,280
Unrealized Gains	0	2
Unrealized Losses	(11)	(3)
Fair Value	8,070	11,279
Current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	113,852	141,678
Unrealized Gains	0	2
Unrealized Losses	(119)	(62)
Fair Value	113,733	141,618
Current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	44,421	19,533
Unrealized Gains	0	0
Unrealized Losses	(57)	(23)
Fair Value	44,364	19,510
Current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	155,222	208,285
Unrealized Gains	0	3
Unrealized Losses	(177)	(135)
Fair Value	155,045	208,153
Non-current:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	466,415	413,123
Unrealized Gains	0	13
Unrealized Losses	(1,389)	(326)
Fair Value	465,026	412,810
Non-current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	960	7,600
Unrealized Gains	0	6
Unrealized Losses	(8)	(13)
Fair Value	952	7,593
Non-current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,165
Unrealized Gains	0
Unrealized Losses	(311)
Fair Value	35,854
Non-current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,992	4,499
Unrealized Gains	0	0
Unrealized Losses	(182)	(21)
Fair Value	23,810	4,478
Non-current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	83,722	20,248
Unrealized Gains	0	0
Unrealized Losses	(524)	(69)
Fair Value	$ 83,198	$ 20,179

Marketable Securities - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Investments, Debt and Equity Securities [Abstract]
Realized gain (loss) on marketable securities	$ 0.0	$ 0.0
Debt securities in an unrealized loss position \| security	240	158
Aggregate fair value of debt securities in an unrealized loss position	$ 439.4	$ 335.4

Property and Equipment, net - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 43,828	$ 38,709
Less: accumulated depreciation	(19,397)	(13,372)
Total property and equipment, net	24,431	25,337
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	17,524	14,529
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	4,293	3,204
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	20,322	19,858
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	752	748
Office equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	319	233
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 618	$ 137

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 6,432	$ 5,708	$ 3,342

Accrued Expenses - Summary of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Accrued compensation	$ 15,693	$ 11,092
Accrued research and development costs	14,849	20,266
Accrued professional fees	3,140	476
Accrued other	349	168
Total accrued expenses	$ 34,031	$ 32,002

Commitments and Contingent Liabilities - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) Lawsuit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Rent expense	$ 6,000,000	$ 6,000,000	$ 7,100,000
Standby letter of credit	$ 2,900,000
Milestone payment period	5 years
Accrual from milestones achieved	$ 292,681,000	220,163,000	$ 141,827,000
Legal proceedings \| Lawsuit	0
Minimum
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Royalty remittance range	0.50%
Non-royalty remittance range	7.00%
Maximum
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Royalty remittance range	2.50%
Non-royalty remittance range	25.00%
Accrued Income Receivable
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Accrual from milestones achieved		$ 4,100,000
License Agreement Terms
Schedule Of Commitments And Contingencies Future Maturities [Line Items]
Payment of clinical development related to licensor	$ 1,600,000
Regulatory payment related to licensor	5,400,000
Sales based payment related to licensor	$ 3,700,000

Commitments and Contingent Liabilities - Future Annual Minimum Lease Payments Due Under Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2018	$ 11,295
2019	11,770
2020	12,077
2021	12,392
2022	14,447
Thereafter	33,891
Total minimum lease payments	$ 95,872

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

Collaboration Agreements - Co-Development and Co-Commercialization Agreements (Details) - Co-Development and Co-Commercialization Agreements	May 17, 2016
Other Than 65/35 Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	50.00%
Celgene \| 65/35 Program
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Profit or loss share percentage	65.00%

Collaboration Agreements - Financial Terms (Details) - Celgene - 2016 Agreement		1 Months Ended	12 Months Ended
	May 17, 2016 USD ($)	May 31, 2016 extension	Dec. 31, 2017 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 200,000,000		$ 8,000,000
Extension period \| extension		2
Number of allowable special case extensions \| extension		4
Upfront payment agreement extension fee receivable	40,000,000
Designation fee	8,000,000
Option exercise fee receivable	30,000,000
Additional option exercise fee for further development	10,000,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum option exercise fee receivable for continuation program	$ 35,000,000

Collaboration Agreements - 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 ($)	Apr. 27, 2015	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 10,000,000
Milestone-based receivable payments, eligible to be received	70,000,000
Milestone payment for filing of first NDA	15,000,000	$ 15,000,000
Milestone payments upon achievement of specified regulatory milestone events	$ 55,000,000

Collaboration Agreements - 2010 Agreement (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty revenue	$ 1,937,000	$ 0	$ 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
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	Jul. 31, 2014 USD ($) unit_of_accounting
Program Licenses \| July 2014 modification \| Upon delivery of the licenses to Celgene, which occurred in January 2015 \| Ivosidenib agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 21.2
Unit(s) of Accounting \| unit_of_accounting			1
Program Licenses \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements \| 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) \| July 2014 modification \| Proportionally as services are delivered over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 50.8
Unit(s) of Accounting \| unit_of_accounting			5
On-Going Development Services (Principal) \| July 2014 modification \| Ratably over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 13.6
Unit(s) of Accounting \| unit_of_accounting			1
On-Going Development Services (Principal) \| April 2015 modification (supplants undelivered elements of July 2014 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) \| $		$ 12.7
Unit(s) of Accounting \| unit_of_accounting		4
On-Going Development Services (Principal) \| April 2015 modification (supplants undelivered elements of July 2014 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) \| 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) \| $	$ 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 Research and Development Services (Agent) \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Proportionally as services are delivered over the performance period, expected to be through December 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 Research and 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 December 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 \| July 2014 modification \| Ratably over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 0.2
Unit(s) of Accounting \| unit_of_accounting			1
Committee Participations \| April 2015 modification (supplants undelivered elements of July 2014 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) \| $		$ 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								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue	$ 9,799	$ 11,358	$ 11,346	$ 10,508	$ 22,648	$ 8,985	$ 6,978	$ 31,281	$ 43,011	$ 69,892	$ 59,119
Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									38,120	43,530	57,043
Program Licenses \| July 2014 modification \| Ivosidenib agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	0	15,808
Program Licenses \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	1,356	11,968
On-Going Development Services (Principal) \| July 2014 modification \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	0	14,711
On-Going Development Services (Principal) \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	1,656	1,719
On-Going Development Services (Principal) \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									11,827	21,308	0
On-Going Research and Development \| July 2014 modification \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	0	4,992
On-Going Research and Development \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	4,584	7,644
On-Going Research and Development \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									26,126	14,445	0
Committee Participations \| July 2014 modification \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	0	80
Committee Participations \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	89	121
Committee Participations \| May 2016 modification (supplants undelivered elements of April 2015 modification) \| Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									$ 167	$ 92	$ 0

Collaboration Agreements - Summary of Revenue Recognized as a Reduction of Research and Development Expenses (Details) - Research and development expense - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	$ 7,797	$ 13,118	$ 17,122
April 2015 modification (supplants undelivered elements of July 2014 modification) \| On-Going Research and Development Services (Agent)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	0	7,456	17,122
May 2016 modification (supplants undelivered elements of April 2015 modification) \| On-Going Research and Development Services (Agent)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total reduction of research and development expenses	$ 7,797	$ 5,662	$ 0

Collaboration Agreements - Development and Commercialization Expense not Contemplated as Part of Modifications (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue	$ 9,799	$ 11,358	$ 11,346	$ 10,508	$ 22,648	$ 8,985	$ 6,978	$ 31,281	$ 43,011	$ 69,892	$ 59,119
Collaborative arrangement, product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									38,120	43,530	57,043
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Development Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									0	1,192	2,076
Total reduction of research and development expenses									14	6,596	8,051
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Commercial Activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total revenue									$ 2,954	$ 170	$ 0

Collaboration Agreements - Collaboration Revenue and Research and Development Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue Recognition and Deferred Revenue [Abstract]
Collaboration revenue - related party	$ 41,074	$ 44,892	$ 59,119
Reduction of research and development costs	7,811	19,714	$ 25,173
Collaboration receivable	$ 2,448	$ 4,886

Collaboration Agreements - Accounting Analysis and Revenue Recognition - Milestone (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2015	Apr. 27, 2015
IDHIFA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue	$ 25,000,000	$ 0	$ 0
AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment for filing of first NDA		$ 15,000,000		$ 15,000,000

Collaboration Agreements - Aurigene Discovery Technologies Limited (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Apr. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accrual from milestones achieved		$ 292,681	$ 220,163	$ 141,827
Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accrual from milestones achieved	$ 3,000	3,000
Potential future milestone payments					$ 17,000
DHODH Phase One Clinical Trial \| Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone payments		$ 2,000

Common Stock - Additional Information (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Common stock, shares authorized (in shares)	125,000,000	125,000,000

Share-Based Payments - Additional Information (Details) - USD ($)		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase shares of common stock (in shares)		1,620,652
Tax benefits related to stock based compensation		$ 0	$ 0	$ 0
Expected contractual term		10 years
Expected dividend yield		0.00%	0.00%	0.00%
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option		$ 2,400,000
Weighted-average period to recognize compensation expense		1 year 2 months 9 days
Performance-Based Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option		$ 9,300,000
2007 Plan and 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based awards reserved for issuance (in shares)		7,206,938
Shares available for future issuance under 2013 ESPP (in shares)		1,327,606
2013 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in common stock (in shares)		2,000,000
Percentage of outstanding shares of common stock (in shares)		4.00%
Weighted-average grant date fair value of options (in usd per share)		$ 35.24	$ 28.41	$ 65.38
Intrinsic value of options exercised		$ 31,500,000	$ 26,400,000	$ 50,900,000
Total unrecognized compensation expense related to stock option		$ 85,300,000
Weighted-average period to recognize compensation expense		2 years 4 months 30 days
2013 Stock Incentive Plan \| Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase shares of common stock (in shares)		0	0	0
Employee Stock Purchase Plan 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance under 2013 ESPP (in shares)		213,791
Stock purchase offering period		6 months
Purchase price discount rate for stock options		85.00%
Shares issued under 2013 ESPP (in shares)		59,651	36,680
Opportunity to purchase common stock (in shares)		327,272
Subsequent Event \| 2013 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized for issuance (in shares)	1,953,046

Share-Based Payments - Summary of Company's Stock Option Activity of all Stock Incentive Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of stock options, outstanding, beginning balance (in shares)	5,218,880
Number of stock options, granted (in shares)	1,620,652
Number of stock options, exercised (in shares)	(730,478)
Number of stock options, forfeited/expired (in shares)	(531,492)
Number of stock options, outstanding, ending balance (in shares)	5,577,562	5,218,880
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)	$ 46.79
Weighted-average exercise price, granted (in usd per share)	51.78
Weighted-average exercise price, exercised (in usd per share)	16.42
Weighted-average exercise price, forfeited/expired (in usd per share)	74.48
Weighted-average exercise price, outstanding, ending balance (in usd per share)	$ 49.58	$ 46.79
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average remaining contractual term, outstanding (in years)	7 years 3 months 9 days	7 years 3 months 11 days
Aggregate intrinsic value, outstanding	$ 94,336	$ 63,559
Number of stock options, exercisable (in shares)	2,936,068
Weighted-average exercise price, exercisable (in usd per share)	$ 44.32
Weighted-average remaining contractual term, exercisable (in years)	5 years 11 months 24 days
Aggregate intrinsic value, exercisable	$ 74,229
Number of stock options, vested and expected to vest (in shares)	5,577,562
Weighted-average exercise price, vested and expected to vest (in usd per share)	$ 49.58
Weighted-average remaining contractual term, vested and expected to vest (in years)	7 years 3 months 9 days
Aggregate intrinsic value, vested and expected to vest	$ 94,336

Share-Based Payments - Summary of Unvested RSUs Activity (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (in shares) \| shares	(7,500)
Restricted stock units
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	66,334
Forfeited (in shares) \| shares	(10,300)
Unvested shares end of period (in shares) \| shares	125,584
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 shares) \| $ / shares	$ 49.60
Weighted-average grant date fair value, granted (in shares) \| $ / shares	52.23
Weighted-average grant date fair value, vested (in shares) \| $ / shares	122.22
Weighted-average grant date fair value, forfeited/expired (in shares) \| $ / shares	39.76
Weighted-average grant date fair value, unvested shares end of period (in shares) \| $ / shares	$ 47.46

Share-Based Payments - Schedule of Performance-Based Units (Details)	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Vested (in shares)	(7,500)
Performance-Based Stock Units (PSUs)
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)	200,613
Granted (in shares)	18,667
Vested (in shares)	0
Forfeited (in shares)	(43,094)
Unvested shares end of period (in shares)	176,186
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, unvested shares beginning of period (in shares) \| $ / shares	$ 53.36
Weighted-average grant date fair value, granted (in shares) \| $ / shares	52.75
Weighted-average grant date fair value, vested (in shares) \| $ / shares	0.00
Weighted-average grant date fair value, forfeited/expired (in shares) \| $ / shares	54.63
Weighted-average grant date fair value, unvested shares end of period (in shares) \| $ / shares	$ 52.98

Share-Based Payments - Schedule of Stock-Based Compensation by Award Type Included Within the Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 47,809	$ 42,086	$ 31,963
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	43,997	39,305	30,331
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	2,858	1,964	902
Performance-based stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	0	46	341
Employee stock purchase plan shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 954	$ 771	$ 389

Share-Based Payments - Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units, Performance-Based Stock Options, Performance-Based Stock Units and Employee Stock Purchase Plan Shares (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 47,809	$ 42,086	$ 31,963
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	30,807	25,386	17,419
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share based compensation expense	$ 17,002	$ 16,700	$ 14,544

Share-Based Payments - Schedule of Grant Date Fair Value Option Award Weighted Average Assumptions Used (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	2.05%	1.42%	1.71%
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	6 years 18 days	6 years 18 days	6 years 15 days
Expected volatility	77.73%	72.84%	69.62%

Income Taxes - Schedule of Domestic and Foreign Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (290,423)	$ (179,896)	$ (111,057)
Foreign	(24,247)	(18,575)	(6,674)
Total	$ (314,670)	$ (198,471)	$ (117,731)

Income Taxes - Reconciliation of Expected Income Tax Benefit (Expense) Computed Using Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax benefit computed at federal statutory tax rate	35.00%	35.00%	35.00%
State taxes, net of federal benefit	4.00%	2.90%	4.50%
Change in valuation allowance	(19.40%)	(43.40%)	(44.60%)
General business credits and other credits	10.40%	9.50%	8.40%
Permanent differences and other adjustments	0.00%	(0.30%)	(0.30%)
Incentive stock options	0.30%	(1.80%)	(1.80%)
Foreign rate differential	(1.60%)	(1.90%)	(1.20%)
Impact of federal rate change	(28.70%)	0.00%	0.00%
Total	0.00%	0.00%	0.00%

Income Taxes - Company's Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 131,165	$ 126,077
Deferred revenue	41,243	8,051
Tax credit carryforwards	100,791	43,350
Purchased intangible assets	3,906	4,410
Stock-based compensation	20,539	22,731
Deferred rent	5,042	8,516
Non-deductible accruals and reserves	3,778	3,310
Total deferred tax assets	306,464	216,445
Depreciation and amortization	(4,549)	(8,412)
Less: valuation allowance	(301,915)	(208,033)
Net deferred taxes	$ 0	$ 0

Income Taxes - Additional Information (Details)	12 Months Ended
Income Taxes - Additional Information (Details)	Dec. 31, 2017 USD ($) Audit	Dec. 31, 2016 USD ($) Audit	Dec. 31, 2015 USD ($)	Dec. 31, 2011 Ownership	Mar. 31, 2017 USD ($)
Income Taxes Disclosure [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Adjustment to income tax expense related to tax reform	$ 90,000,000
Percentage of stock owned resulting in an ownership change	50.00%
Aggregate period	3 years
Number of ownership changes \| Ownership				2
Valuation allowance	$ 301,915,000	208,033,000
Increase in valuation allowance	$ 93,900,000	$ 86,100,000	$ 52,500,000
Number of federal, state or foreign audits in process \| Audit	0	0
Percentage of increase in stockholders ownership	5.00%
ASU 2016-09
Income Taxes Disclosure [Line Items]
Increase in deferred tax assets	$ 32,700,000				$ 32,700,000
Valuation allowance					$ 32,700,000
Federal Orphan Drug Tax Credit
Income Taxes Disclosure [Line Items]
Research and development tax credit	75,600,000
Federal
Income Taxes Disclosure [Line Items]
Net operating loss	454,600,000
Federal \| Research Tax Credit Carryforward
Income Taxes Disclosure [Line Items]
Research and development tax credit	18,500,000
State and Local Jurisdiction
Income Taxes Disclosure [Line Items]
Net operating loss	456,700,000
State and Local Jurisdiction \| Research Tax Credit Carryforward
Income Taxes Disclosure [Line Items]
Research and development tax credit	8,500,000
Foreign Income Tax
Income Taxes Disclosure [Line Items]
Net operating loss	$ 46,200,000

Income Taxes - Unrecognized Tax Benefits Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at December 31, 2016	$ 0	$ 0
Gross increases - current period tax positions	11,263	0
Unrecognized tax benefits at December 31, 2017	$ 11,263	$ 0

Defined Contribution Benefit Plan - Additional Information (Details)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Employer's matching contribution percentage	50.00%
Employer's contribution percentage of eligible compensation	6.00%

Net Loss per Share - Additional Information (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,725,208	5,319,948	4,641,418
Performance-based stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	176,186

Net Loss per Share - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,725,208	5,319,948	4,641,418
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,577,562	5,218,880	4,618,697
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)	125,584	77,050	15,000
Unvested restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	0	0	0
Employee stock purchase plan shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	22,062	24,018	7,721

Selected Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 9,799	$ 11,358	$ 11,346	$ 10,508	$ 22,648	$ 8,985	$ 6,978	$ 31,281	$ 43,011	$ 69,892	$ 59,119
Loss from operations	(90,130)	(79,017)	(84,600)	(67,047)	(57,409)	(63,512)	(56,470)	(23,594)	$ (320,794)	$ (200,985)	$ (118,700)
Net loss	$ (88,285)	$ (77,137)	$ (83,082)	$ (66,166)	$ (56,486)	$ (62,834)	$ (55,953)	$ (23,198)
Net loss per share - basic and diluted (in usd per share)	$ (1.81)	$ (1.59)	$ (1.78)	$ (1.56)	$ (1.34)	$ (1.63)	$ (1.47)	$ (0.61)	$ (6.75)	$ (5.07)	$ (3.15)

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	Jul. 31, 2014 USD ($) unit_of_accounting
Program Licenses \| July 2014 modification \| Upon delivery of the licenses to Celgene, which occurred in January 2015 \| Ivosidenib agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 21.2
Unit(s) of Accounting \| unit_of_accounting			1
Program Licenses \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Upon delivery of the licenses to Celgene, which occurred immediately upon the execution of the AG-881 Agreements \| 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) \| July 2014 modification \| Proportionally as services are delivered over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 50.8
Unit(s) of Accounting \| unit_of_accounting			5
On-Going Development Services (Principal) \| July 2014 modification \| Ratably over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 13.6
Unit(s) of Accounting \| unit_of_accounting			1
On-Going Development Services (Principal) \| April 2015 modification (supplants undelivered elements of July 2014 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) \| $		$ 12.7
Unit(s) of Accounting \| unit_of_accounting		4
On-Going Development Services (Principal) \| April 2015 modification (supplants undelivered elements of July 2014 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) \| 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) \| $	$ 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 Research and Development Services (Agent) \| April 2015 modification (supplants undelivered elements of July 2014 modification) \| Proportionally as services are delivered over the performance period, expected to be through December 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 Research and 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 December 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 \| July 2014 modification \| Ratably over the performance period, expected to be through June 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Best estimate selling price (BESP) \| $			$ 0.2
Unit(s) of Accounting \| unit_of_accounting			1
Committee Participations \| April 2015 modification (supplants undelivered elements of July 2014 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) \| $		$ 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