0001439222-18-000018 | 10-Q | XBRL Viewer | Agios Pharmaceuticals INC

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 29, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	AGIOS PHARMACEUTICALS INC
Trading Symbol	AGIO
Entity Central Index Key	0001439222
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		58,178,676

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 156,478	$ 102,724
Marketable securities	513,414	321,212
Accounts receivable, net	2,631	0
Collaboration receivable – related party	3,395	2,448
Collaboration receivable – other	440	0
Royalty receivable – related party	1,863	1,222
Inventory	863	0
Prepaid expenses and other current assets	16,458	17,655
Total current assets	695,542	445,261
Marketable securities	208,508	143,814
Property and equipment, net	24,613	24,431
Other non-current assets	416	891
Total assets	929,079	614,397
Current liabilities:
Accounts payable	16,616	22,767
Accrued expenses	25,303	34,031
Deferred revenue – related party	42,141	37,842
Deferred rent	686	301
Total current liabilities	84,746	94,941
Deferred revenue, net of current portion – related party	66,294	125,798
Deferred rent, net of current portion	17,826	18,155
Total liabilities	168,866	238,894
Stockholders’ equity:
Preferred stock, $0.001 par value; 25,000,000 shares authorized; no shares issued or outstanding at September 30, 2018 and December 31, 2017	0	0
Common stock, $0.001 par value; 125,000,000 shares authorized; 58,167,932 and 48,826,153 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	58	49
Additional paid-in capital	1,775,113	1,174,904
Accumulated other comprehensive loss	(2,119)	(1,389)
Accumulated deficit	(1,012,839)	(798,061)
Total stockholders’ equity	760,213	375,503
Total liabilities and stockholders’ equity	$ 929,079	$ 614,397

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in usd per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	25,000,000	25,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued (in shares)	58,167,932	48,826,153
Common stock, shares outstanding (in shares)	58,167,932	48,826,153

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Revenues	$ 15,198	$ 11,358	$ 64,374	$ 33,212
Costs and expenses:
Cost of sales	695	0	695	0
Research and development (net of $1,078 and $6,343 of cost reimbursement from related party for the three and nine months ended September 30, 2017)	82,561	72,917	247,515	215,465
Sales, general and administrative	31,104	17,458	82,287	48,411
Total costs and expenses	114,360	90,375	330,497	263,876
Loss from operations	(99,162)	(79,017)	(266,123)	(230,664)
Interest income	4,498	1,880	11,889	4,279
Net loss	$ (94,664)	$ (77,137)	$ (254,234)	$ (226,385)
Net loss per share – basic and diluted (usd per share)	$ (1.63)	$ (1.59)	$ (4.45)	$ (4.94)
Weighted-average number of common shares used in computing net loss per share – basic and diluted (in shares)	58,033,386	48,459,424	57,158,492	45,851,203
Product revenue, net
Revenues:
Revenues	$ 4,465	$ 0	$ 4,465	$ 0
Collaboration revenue - related party
Revenues:
Revenues	8,732	10,643	42,478	32,497
Collaboration revenue - other
Revenues:
Revenues	0	0	12,440	0
Royalty revenue - related party
Revenues:
Revenues	$ 2,001	$ 715	$ 4,991	$ 715

Condensed Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Related party research and development expense	$ 0	$ 1,078	$ 0	$ 6,343

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (94,664)	$ (77,137)	$ (254,234)	$ (226,385)
Other comprehensive income (loss)
Unrealized gain (loss) on available-for-sale securities	279	135	(730)	(202)
Comprehensive loss	$ (94,385)	$ (77,002)	$ (254,964)	$ (226,587)

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (254,234)	$ (226,385)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	5,261	4,778
Stock-based compensation expense	55,170	35,128
Net amortization of premium and discounts on investments	(2,540)	25
(Gain) loss on disposal of property and equipment	(20)	40
Changes in operating assets and liabilities:
Accounts receivable, net	(2,631)	0
Collaboration receivable – related party	(947)	1,397
Collaboration receivable – other	(440)	0
Royalty receivable – related party	(641)	(715)
Inventory	(863)	0
Prepaid expenses and other current and non-current assets	1,711	(1,886)
Accounts payable	(5,830)	742
Accrued expenses	(8,537)	(1,242)
Deferred revenue – related party	(15,749)	(20,141)
Deferred rent	56	(2,519)
Net cash used in operating activities	(230,234)	(210,778)
Investing activities
Purchases of marketable securities	(755,368)	(604,525)
Proceeds from maturities and sales of marketable securities	500,281	508,116
Purchases of property and equipment	(5,933)	(3,347)
Net cash used in investing activities	(261,020)	(99,756)
Financing activities
Payment of public offering costs, net of reimbursements	(391)	(89)
Proceeds from public offering of common stock, net of commissions	516,206	270,250
Net proceeds from stock option exercises and employee stock purchase plan	29,193	12,360
Net cash provided by financing activities	545,008	282,521
Net change in cash and cash equivalents	53,754	(28,013)
Cash and cash equivalents at beginning of the period	102,724	160,754
Cash and cash equivalents at end of the period	156,478	132,741
Supplemental disclosure of non-cash investing and financing transactions
Additions to property and equipment in accounts payable and accrued expenses	501	226
Proceeds from stock option exercises in other current assets	39	95
Public offering costs in other current assets, net of amounts in accounts payable and accrued expenses	$ 0	$ 318

Overview and Basis of Presentation	9 Months Ended
Overview and Basis of Presentation	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Overview and Basis of Presentation	Overview and Basis of Presentation References to Agios Throughout this Quarterly Report on Form 10-Q, “we,” “us,” and “our,” and similar expressions, except where the context requires otherwise, refer to Agios Pharmaceuticals, Inc. and its consolidated subsidiaries, and “our Board of Directors” refers to the board of directors of Agios Pharmaceuticals, Inc. Overview We are a biopharmaceutical company committed to the fundamental transformation of patients’ lives through scientific leadership in the field of cellular metabolism, with the goal of making transformative, first- or best-in-class medicines. Our therapeutic areas of focus are cancer and rare genetic diseases, or RGDs, which are diseases that are directly caused by changes in genes or chromosomes, often passed from one generation to the next. Most RGDs are often associated with severe or life-threatening features. The incidence of a single RGD can vary widely but is generally very infrequent, usually equal to or less than one per 100,000 births. In both areas of cancer and RGDs, we are seeking to unlock the biology of cellular metabolism as a platform to create transformative therapies. We are located in Cambridge, Massachusetts. Basis of presentation The condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of our management, reflect all adjustments, which include only normal recurring adjustments, necessary to fairly state our financial position as of September 30, 2018, our results of operations for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017. The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three and nine-month period are also unaudited. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The year-end condensed consolidated balance sheet data was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. Accordingly, the condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2017 that was filed with the Securities and Exchange Commission, or the SEC, on February 14, 2018. Our condensed 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 condensed consolidated financial statements have been prepared in conformity with U.S. GAAP. Liquidity In January 2018, we completed a public offering of 8,152,986 shares of common stock at an offering price of $67.00 per share. We received net proceeds from this offering of $516.2 million, after deducting underwriting discounts and commissions paid by us. As of September 30, 2018, we had cash, cash equivalents and marketable securities of $878.4 million. Although we have incurred recurring losses and expect to continue to incur losses for the foreseeable future, we expect our cash, cash equivalents and marketable securities will be sufficient to fund current operations for at least the next twelve months from the issuance date of these financial statements.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies and Recent Accounting Pronouncements

Significant accounting policies

Accounts receivable, net

Our trade accounts receivable arise from product sales and represent amounts due from specialty distributors and specialty pharmacy providers in the U.S. We monitor the financial performance and creditworthiness of our customers so that we can

properly assess and respond to changes in their credit profile. We reserve against these receivables for estimated losses that may arise from a customer’s inability to pay. Amounts determined to be uncollectible are charged or written-off against the reserve.

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 receivables, including trade receivables from our customers and collaboration and royalty receivables from Celgene Corporation, or Celgene, and CStone Pharmaceuticals, or CStone. Concentrations of credit risk with respect to receivables, which are typically unsecured, are somewhat mitigated due to the number of customers using our products. Our trade receivables arise from product sales in the U.S. and have standard payment terms that generally require payment within 30 to 60 days. We have evaluated the creditworthiness of our customers, including Celgene, and determined them to be creditworthy. To date we have not experienced any losses with respect to our receivables.

Inventory

Inventory is stated at the lower of cost or estimated net realizable value on a first-in, first-out basis. Prior to the regulatory approval of our product candidates, we incur expenses for the manufacture of drug product that could potentially be available to support the commercial launch of those products. Until the date at which regulatory approval has been received or is otherwise considered probable, we record all such costs as research and development expenses. Our wholly owned product, TIBSOVO® (ivosidenib), received approval from the U.S. Food and Drug Administration, or FDA, on July 20, 2018 for the treatment of adult patients with relapsed or refractory acute myeloid leukemia, or R/R AML, with susceptible isocitrate dehydrogenase 1, or IDH1, mutation as detected by an FDA-approved test, and we began to capitalize inventories of TIBSOVO® beginning on July 20, 2018.

We perform an assessment of the recoverability of capitalized inventory during each reporting period and write down any excess and obsolete inventory to its estimated net realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded as a component of cost of sales in the condensed consolidated statements of operations. The determination of whether inventory costs will be realizable requires the use of estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required.

Revenue from Contracts with Customers

In May 2014, the Financial Accounting Standards Board, or FASB, issued Accounting Standards Update, or ASU, No. 2014-09, Revenue from Contracts with Customers (Topic 606), which was codified as Accounting Standards Codification 606, Revenue from Contracts with Customers, or ASC 606, and amended through subsequent ASUs. We adopted ASC 606 effective January 1, 2018 using the modified retrospective method. Under this method, we recognized the cumulative effect of the change in the opening balance of accumulated deficit in the current period condensed consolidated balance sheet.

Upon finalization of our assessment, which resulted in changes to our estimates as of December 31, 2017, the impact of the cumulative effect of the accounting changes upon the adoption of the standard (in thousands) is as follows:


	December 31, 2017		Cumulative Effect		January 1, 2018
Deferred revenue – related party, current and net of current portions	$	163,640	$	(39,456)	$	124,184
Accumulated deficit	(798,061)		39,456		(758,605)

The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements (in thousands, except per share data):

Condensed Consolidated Balance Sheets


	September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change
Accounts receivable, net	$	2,631	$	2,631	$	—
Collaboration receivable – related party	3,395		3,395		—
Collaboration receivable – other	440		—		440
Total current assets	695,542		695,102		440
Total assets	929,079		928,639		440

Deferred revenue – related party	42,141		33,648		8,493
Total current liabilities	84,746		76,253		8,493
Deferred revenue, net of current portion – related party	66,294		107,714		(41,420)

Total liabilities	168,866		201,793		(32,927)
Accumulated deficit	(1,012,839)		(1,046,206)		33,367
Total stockholders’ equity	760,213		726,846		33,367
Total liabilities and stockholders’ equity	929,079		928,639		440

Condensed Consolidated Statements of Operations


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Product revenue, net	$	4,465	$	4,465	$	—	$	4,465	$	4,465	$	—
Collaboration revenue – related party	8,732		10,137		(1,405)		42,478		46,096		(3,618)
Collaboration revenue – other	—		—		—		12,440		12,000		440
Research and development expense	82,561		81,714		847		247,515		244,604		2,911
Total cost and expenses	114,360		113,513		847		330,497		327,586		2,911
Loss from operations	(99,162)		(96,910)		(2,252)		(266,123)		(260,034)		(6,089)
Net loss	(94,664)		(92,412)		(2,252)		(254,234)		(248,145)		(6,089)
Net loss per share – basic and diluted	(1.63)		(1.59)		(0.04)		(4.45)		(4.34)		(0.11)

Condensed Consolidated Statements of Comprehensive Loss


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Net loss	$	(94,664)	$	(92,412)	$	(2,252)	$	(254,234)	$	(248,145)	$	(6,089)
Comprehensive loss	(94,385)		(92,133)		(2,252)		(254,964)		(248,875)		(6,089)

Condensed Consolidated Statements of Cash Flows


	Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change
Net loss	$	(254,234)	$	(248,145)	$	(6,089)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable, net	(2,631)		(2,631)		—
Collaboration receivable – related party	(947)		(947)		—
Collaboration receivable – other	(440)		—		(440)
Deferred revenue – related party	(15,749)		(22,278)		6,529

Cost of Sales

Cost of sales consists primarily of manufacturing costs of TIBSOVO®. Based on our policy to expense costs associated with the manufacturing of our products prior to regulatory approval, certain of the manufacturing costs associated with product shipments of TIBSOVO® recorded during the three and nine months ended September 30, 2018 were expensed prior to July 20, 2018 and, therefore, are not included in costs of sales during the current period.

Recent accounting pronouncements

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which was codified as ASC 842, Leases, and amended through subsequent ASUs.

We are in the process of reviewing our existing lease contracts and continue to evaluate the accounting implications of ASC 842. We will adopt the guidance effective January 1, 2019 using the modified retrospective transition approach and we expect to elect the package of practical expedients, both provided for under ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. The package of practical expedients allows us not to reassess whether contracts are or contain leases, lease classification, and whether initial direct costs qualify for capitalization.

Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption.

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

We record cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures, establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our own assumptions (unobservable inputs). The hierarchy consists of three levels:

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

Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, directly or indirectly, for substantially the full term of the asset or liability.

Level 3 – Unobservable inputs that reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2018 (in thousands):


	Level 1		Level 2		Level 3		Total
Cash equivalents	$	129,123	$	24,001	$	—	$	153,124
Marketable securities:
Certificates of deposit	—		954		—		954
U.S. Treasuries	—		266,119		—		266,119
Government securities	—		114,407		—		114,407
Corporate debt securities	—		340,442		—		340,442
Total cash equivalents and marketable securities	$	129,123	$	745,923	$	—	$	875,046

Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently, at the end of each reporting period, valued utilizing third-party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches, and observable market inputs to determine value. After completing our validation procedures, we did not adjust or override any fair value measurements provided by the pricing services as of September 30, 2018.

There have been no changes to the valuation methods during the nine months ended September 30, 2018. We evaluate transfers between levels at the end of each reporting period. There were no transfers between Level 1 and Level 2 during the nine months ended September 30, 2018. We have no financial assets or liabilities that were classified as Level 3 at any point during the nine months ended September 30, 2018.

- Definition

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

+ References + Details

Marketable Securities

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable SecuritiesOur marketable securities are classified as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities, and are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive loss in stockholders’ equity and a component of total comprehensive loss in the condensed consolidated statements of

comprehensive loss, until realized. Realized gains and losses are included in investment income on a specific-identification basis. There were no realized gains or losses on marketable securities for the three and nine months ended September 30, 2018 and 2017 and, as a result, there were no reclassifications of any amounts out of accumulated other comprehensive loss for those periods.

Marketable securities at September 30, 2018 consisted of the following (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Current:
Certificates of deposit	$	960	$	—	$	(6)	$	954
U.S Treasuries	244,818		—		(302)		244,516
Government securities	61,522		—		(163)		61,359
Corporate debt securities	206,948		—		(363)		206,585
Non-current:
Certificates of deposit	—		—		—		—
U.S Treasuries	21,860		—		(257)		21,603
Government securities	53,301		—		(253)		53,048
Corporate debt securities	134,632		—		(775)		133,857
Total marketable securities	$	724,041	$	—	$	(2,119)	$	721,922

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
Total marketable securities	$	466,415	$	—	$	(1,389)	$	465,026

At September 30, 2018 and December 31, 2017, we held both current and non-current investments. Investments classified as current have maturities of less than one year. Investments classified as non-current are those that: (i) have a maturity of one year to two years, and (ii) we do not intend to liquidate within the next twelve months, although these funds are available for use and therefore classified as available-for-sale.

At September 30, 2018 and December 31, 2017, we held 236 and 240 debt securities that were in an unrealized loss position for less than one year, respectively. The aggregate fair value of debt securities in an unrealized loss position at September 30, 2018 and December 31, 2017 was $659.8 million and $439.4 million, respectively. There were no individual securities that were in a significant unrealized loss position as of September 30, 2018 and December 31, 2017. Given our intent and ability to hold such securities until recovery, and the lack of material of change in the credit risk of these investments, we do not consider these marketable securities to be other-than-temporarily impaired as of September 30, 2018 and December 31, 2017.

Inventory

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Inventory

Inventory consists of the following (in thousands):


	September 30, 2018
Raw materials	$	—
Work-in-process	788
Finished goods	75
Total Inventory	$	863

Inventory is related to our approved product, TIBSOVO®. There were no write downs for excess and obsolete inventory during the three months ended September 30, 2018.

Accrued Expenses

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Accrued Expenses

Accrued expenses consist of the following (in thousands):


	September 30, 2018		December 31, 2017
Accrued compensation	$	11,748	$	15,693
Accrued research and development costs	10,535		14,849
Accrued professional fees	2,509		3,140
Accrued other	511		349
Total accrued expenses	$	25,303	$	34,031

Product Revenue

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Product Revenue

Our wholly owned product, TIBSOVO®, received approval from the FDA on July 20, 2018 for the treatment of adult patients with R/R AML with a susceptible IDH1 mutation. Upon FDA approval of TIBSOVO® in the U.S. we began generating product revenue from sales of TIBSOVO®. We sell TIBSOVO® to a limited number of specialty distributors and specialty pharmacy providers in the U.S., or collectively, the Customers. The Customers subsequently resell TIBSOVO® to pharmacies or dispense directly to patients. In addition to distribution agreements with Customers, we enter into arrangements with healthcare providers and payors that provide for government-mandated and/or privately-negotiated rebates, chargebacks and discounts with respect to the purchase of TIBSOVO®.

The performance obligation related to the sale of TIBSOVO® is satisfied and revenue is recognized when the Customer obtains control of the product, which occurs at a point in time, typically upon delivery to the Customer.

Reserves for Variable Consideration

Revenues from product sales are recorded at the net sales price, or transaction price, which includes estimates of variable consideration for which reserves are established and result from contractual adjustments, government rebates, returns and other allowances that are offered within the contracts with our Customers, healthcare providers, payors and other indirect customers relating to the sale of our products.

Contractual Adjustments

We generally provide Customers with discounts, including prompt pay discounts, and allowances that are explicitly stated in the contracts and are recorded as a reduction of revenue in the period the related product revenue is recognized. In addition, we receive sales order management, data and distribution services from certain Customers.

Chargebacks for fees and discounts represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to Customers who directly purchase the product from us. Customers charge us for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These reserves are estimated using the expected value method, based upon a range of possible outcomes that are probability-weighted for the estimated channel mix and are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue.

Government Rebates

Government rebates consist of Medicare, TriCare, and Medicaid rebates, which we estimate using the expected value method, based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue. For Medicare, we also estimate the number of patients in the prescription drug coverage gap for whom we will owe an additional liability under the Medicare Part D program.

Returns

We estimate the amount of product sales that may be returned by Customers and record this estimate as a reduction of revenue in the period the related product revenue is recognized. We currently estimate product return liabilities using the expected value method, based on available industry data, including our visibility into the inventory remaining in the distribution channel.

To date, our source of product revenue has been U.S. sales of TIBSOVO®. Total net product revenue was $4.5 million for the three and nine months ended September 30, 2018, respectively. The following table summarizes balances and activity in each of the product revenue allowance and reserve categories for the nine months ended September 30, 2018 (in thousands):


	Contractual Adjustments		Government Rebates		Returns		Total
Balance at December 31, 2017	$	—	$	—	$	—	$	—
Current provisions relating to sales in the current year	360		135		106		601

Payments/returns relating to sales in the current year	(180)		—		—		(180)

Balance at September 30, 2018	$	180	$	135	$	106	$	421

Total revenue-related reserves above, included in our condensed consolidated balance sheets, are summarized as follows (in thousands):


	September 30, 2018
Reduction of accounts receivable	$	98
Component of accrued expenses	323
Total revenue-related reserves	$	421

The following table presents changes in our contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Accounts receivable, net	$	—	$	5,328	$	(2,697)	$	2,631

(1) Additions to contract assets relate to amounts billed to Customers for product sales during the reporting period. Deductions to contract assets relate to collection of receivables during the reporting period.

Collaboration and License Agreements

9 Months Ended

Sep. 30, 2018

Revenue Recognition and Deferred Revenue [Abstract]

Collaboration and License Agreements

Celgene Corporation

To date, our revenue has primarily been generated from our collaboration agreements with Celgene, or collectively, the Collaboration Agreements. Celgene is a related party through ownership of our common stock. In April 2010, we entered into a discovery and development collaboration and license agreement focused on cancer metabolism, or the 2010 Agreement. The 2010 Agreement was amended in October 2011 and July 2014. In April 2015, we entered into a joint worldwide development and profit share collaboration and license agreement with Celgene, and our wholly owned subsidiary, Agios International Sarl, entered into a collaboration and license agreement with Celgene International II Sarl, or collectively, the AG-881 Agreements, to establish a worldwide collaboration focused on the development and commercialization of AG-881 products. The AG-881 Agreements were terminated effective September 4, 2018. In May 2016, we entered into a master research and collaboration agreement with Celgene, or the 2016 Agreement.

2016 Agreement

In May 2016, we entered into the 2016 Agreement focused on metabolic immuno-oncology, or MIO, a developing field which aims to modulate the activity of relevant immune cells by targeting critical metabolic nodes, thereby enhancing the immune mediated anti-tumor response. In addition to new programs identified under the 2016 Agreement, both parties also agreed that all future development and commercialization of two remaining cancer metabolism programs discovered under the 2010 Agreement, including AG-270, an inhibitor of methionine adenosyltransferase 2a, will now be governed by the 2016 Agreement.

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

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

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

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

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

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

Co-development and co-commercialization agreements

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

License agreements

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

Financial terms

Under the terms of the 2016 Agreement, we received an initial upfront payment in the amount of $200.0 million. The 2016 Agreement provides specified rights to extend the research term for up to two, or in specified cases, up to four, additional years

by paying a $40.0 million per-year extension fee. Celgene will pay an $8.0 million designation fee for each program that Celgene designates for further development and for each continuation program. During the three months ended March 31, 2017, we received $8.0 million from Celgene upon the designation of AG-270 as a development candidate. For each program as to which Celgene exercises its option to develop and commercialize, subject to antitrust clearance, Celgene will pay an option exercise fee of at least $30.0 million for any designated development program and at least $35.0 million for any continuation programs. In certain cases, Celgene may exercise its option to develop and commercialize two early-stage I&I programs, prior to Celgene designating the program for further development, by paying an option exercise fee of $10.0 million.

We are eligible to receive the following milestone-based payments associated with the 2016 Agreement:

Program

Milestone

Amount

65/35 program in IO field

Specified clinical development event

$25.0 million

65/35 program in IO field

Specified regulatory milestone events

Up to $183.8 million

50/50 program in IO field

Specified clinical development event

$20.0 million

50/50 program in IO field

Specified regulatory milestone events

Up to $148.8 million

I&I field

Specified clinical development event

$25.0 million

I&I field

Specified regulatory milestone events

Up to $236.3 million

I&I field

Specified commercial milestone events

Up to $125.0 million

Additionally, for each licensed program in the I&I field, we are eligible to receive royalties at tiered, low double-digit percentage rates on Celgene’s net sales, if any.

Opt-out right

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

Term

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

Termination

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

Exclusivity

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

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

Ivosidenib Letter Agreement

In May 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 termination, we obtained global rights to ivosidenib and the IDH1 program. Neither party will have any further financial obligation, including royalties or milestone payments, to the other concerning ivosidenib or the IDH1 program. Under the terms of the termination, the parties also agreed to conduct specified transitional activities in connection with the termination. In addition, pursuant to the Ivosidenib Letter Agreement, the parties are released from their exclusivity obligations under the 2010 Agreement with respect to the IDH1 program. The termination did not affect the AG-881 Agreements, which were directed to both the IDH1 target and the isocitrate dehydrogenase 2, or IDH2, target, and were subsequently terminated in September 2018 as discussed below.

Termination of AG-881 Agreements

In September 2018, we and Celgene agreed to terminate the AG-881 Agreements effective as of September 4, 2018. From and after September 4, 2018, we obtained sole global rights to AG-881. Neither we nor Celgene will have any further financial obligation under the AG-881 Agreements, including milestones, royalties or other payments, except that (a) Celgene shall be eligible to receive royalties from us at a low single-digit percentage rate on worldwide net sales of products containing AG-881 and (b) we and Celgene shall split certain agreed-upon worldwide development costs for AG-881 until December 31, 2018. In addition, for a specified period and subject to specified exceptions, Celgene and its affiliates shall be prohibited from developing, manufacturing or commercializing any product that inhibits IDH1 at specified levels of binding for any indication and we shall be prohibited from developing, manufacturing or commercializing AG-881 in hematologic indications.

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® (enasidenib), a co-commercialized licensed program for which Celgene leads and funds global development and commercialization activities. We have exercised our right to participate in a portion of commercialization activities in the United States for IDHIFA® in accordance with the applicable commercialization plan. On August 1, 2017, the FDA granted Celgene approval of IDHIFA® for the treatment of adult patients with R/R AML with an IDH2 mutation as detected by an FDA-approved test.

Under the remaining terms of the 2010 Agreement, we are eligible to receive up to $80.0 million in potential milestone payments for the enasidenib program. The potential milestone payments are comprised of: (i) up to $55.0 million in milestone payments upon achievement of specified ex-U.S. regulatory milestone events, and (ii) a $25.0 million milestone payment upon achievement of a specified ex-U.S. commercial milestone event.

Under the 2010 Agreement, we receive royalties at tiered, low-double digit to mid-teen percentage rates on net sales of IDHIFA®.

Unless terminated earlier by either party, the term of the 2010 Agreement will continue until the expiration of all royalty terms with respect to IDHIFA®. Celgene may terminate this agreement for convenience in its entirety upon ninety days written notice to us. If either party is in material breach and fails to cure such breach within the specified cure period, the other party may terminate the 2010 Agreement in its entirety. Either party may terminate the agreement in the event of specified insolvency events involving the other party.

Accounting analysis and revenue recognition – collaboration revenue

On January 1, 2018 we adopted ASC 606 under the modified retrospective method. Prior to January 1, 2018 we accounted for the Collaboration Agreements under ASC 605-25, Multiple Element Arrangements.

Accounting under ASC 606

In adopting ASC 606, we applied the practical expedient that permits aggregating the effect of all contract modifications that occurred prior to January 1, 2018. No other practical expedients were used. Similar to the accounting under ASC 605-25, the 2016 Agreement was determined to be a modification of the 2010 Agreement and the AG-881 Agreements. In determining the appropriate amount of revenue to be recognized under ASC 606, we performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) we satisfied each performance obligation.

As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price, or SSP, for each performance obligation identified in the contract. We use key assumptions to determine the SSP, which include forecast of revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.

The satisfied and unsatisfied performance obligations at the time of the ASC 606 adoption, each of which are considered by us to be distinct within the context of the contract, their SSP, the method of recognizing the allocated consideration, and the period through which they are expected to be recognized are as follows:

Performance Obligations

SSP

No. of Performance Obligation(s)

Recognition Method

Fully satisfied at time of adoption

Licenses (1)

$86.7 million

Fully satisfied; recognized upon adoption of ASC 606

Research and development services (2)

$350.7 million

Fully satisfied; recognized upon adoption of ASC 606

Partially satisfied at time of adoption

Research and development services (2)

$266.6 million

Proportionally as services are delivered over the performance period, expected to be through September 2022 (3)

(1) The SSP was developed by probability weighting multiple cash flow scenarios using the income approach. Our management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimate of the direct cost incurred to generate future cash flows, a discount rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the SSP of these units of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals, and other factors. If different reasonable assumptions are utilized, the SSP and revenue recognized would vary.

(2) The SSP was developed using our management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider and using internal full time equivalent costs to support the development services.

(3) We determined that recognizing revenue on a proportional basis using the ratio of effort incurred to date compared to the total estimated effort required to complete the performance obligation best depicts the satisfaction of our obligations under the Collaboration Agreements.

During the three and nine months ended September 30, 2018, we recognized the following as collaboration revenue (in thousands):


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
Performance Obligation	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Collaboration revenue - related party
Licenses	$	—	$	—	$	—	$	15,000	$	15,000	$	—
Research and development services	7,504		8,864		(1,360)		23,698		27,184		(3,486)
Committee participation	—		45		(45)		—		132		(132)
Reduction of research and development expenses
Development services	—		847		(847)		—		2,911		(2,911)

During the three and nine months ended September 30, 2018 and 2017, we recognized as collaboration revenue the following non-contingent consideration allocated to each performance obligation (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Licenses	$	—	$	—	$	15,000	$	—
On-going research and development services	7,504		9,708		23,698		30,374
Committee participation	—		41		—		124

Consideration for development and commercialization services performed by us, that were not considered performance obligations as of the modification dates, are recognized as collaboration revenue or a reduction of research and development expenses in the period in which they are earned. There was no impact from the adoption of ASC 606 on these obligations. For the three and nine months ended September 30, 2018 and 2017, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Collaboration revenue - related party
Development activities	$	312	$	—	$	902	$	—
Commercialization activities	916		894		2,878		1,999
Reduction of research and development expenses
Research and development activities	—		—		—		14

For the three and nine months ended September 30, 2018 and 2017, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Collaboration revenue - related party	$	8,732	$	10,643	$	42,478	$	32,497
Reduction of research and development expenses	—		1,078		—		6,343

The following table presents changes in our contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Collaboration receivable – related party	$	2,448	$	26,233	$	(25,286)	$	3,395
Royalty receivable – related party	1,222		4,853		(4,212)		1,863
Contract liabilities (2)
Deferred revenue – related party, current and net of current portions	163,640		7,976		(63,181)		108,435

(1) Additions to contract assets relate to amounts billed to Celgene for reimbursable costs incurred by us during the reporting period. Deductions to contract assets relate to collection of receivables during the reporting period.

(2) Additions to contract liabilities relate to consideration from Celgene during the reporting period. Deductions to contract liabilities relate to deferred revenue recognized as revenue during the reporting period and the cumulative catch-up adjustment recognized upon adoption of ASC 606 on January 1, 2018.

During the three and nine months ended September 30, 2018, we recognized the following as revenue due to changes in the contract liability balances (in thousands):


	September 30, 2018
	Three Months Ended		Nine Months Ended
Amounts included in the contract liability at the beginning of the period	$	7,555	$	23,472
Performance obligations satisfied in previous periods	219		762

As of September 30, 2018, the aggregate amount of the transaction price allocated to performance obligations that are partially unsatisfied was $115.9 million.

We consider the total consideration expected to be earned in the next twelve months for services to be performed as current deferred revenue, and consideration that is expected to be earned subsequent to twelve months from the balance sheet date as non-current deferred revenue.

Accounting analysis and revenue recognition – royalty revenue

For arrangements that include sales-based royalties and sales-based milestones and in which the license is deemed to be the predominant item to which the royalties relate, we recognize royalty revenue upon the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).

As the underlying performance obligation, or delivery of the enasidenib license, had been satisfied as of June 2014, royalty revenue is recognized as the related sales occur. During the three and nine months ended September 30, 2018 and 2017, we recognized the following as royalty revenue (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Royalty revenue – related party	$	2,001	$	715	$	4,991	$	715

Accounting analysis and revenue recognition – milestone revenue

At each reporting period we evaluate whether milestones are considered probable of being reached and, to the extent that a significant reversal would not occur in future periods, estimate the amount to be included in the transaction price using the most likely amount method. Milestone payments that are not within our control, such as regulatory approvals, are not considered probable of being achieved and are excluded from the transaction price until those approvals are received.

During the three months ended June 30, 2018, Celgene submitted an MAA to the EMA for IDHIFA® for IDH2 mutant-positive R/R AML. As a result of the filing, we determined that a $15.0 million milestone payment for filing of a first new drug application equivalent in an ex-U.S. country was considered probable of being reached as of June 30, 2018 and a significant reversal of revenue would not occur in future periods. As the underlying performance obligation, or delivery of the license to enasidenib, had been satisfied as of June 2014, the milestone payment was recognized in full as collaboration revenue during the three months ended June 30, 2018.

No other milestones were achieved during the three months ended September 30, 2018 and three and nine months ended September 30, 2017. The next potential milestone expected to be achieved under our collaboration agreements with Celgene is the first regulatory approval in any of China, Japan or a major European country. Achievement of this event will result in milestone payment of $35.0 million under the 2010 Agreement.

CStone Pharmaceuticals

In June 2018, we entered into an exclusive license agreement with CStone, or the CStone Agreement, to grant CStone specified intellectual property licenses to enable CStone to develop and commercialize certain products containing ivosidenib in mainland China, Hong Kong, Macau, and Taiwan. We retain development and commercialization rights for the rest of the world. Pursuant to the CStone Agreement, CStone will initially be responsible for the development and commercialization of ivosidenib in AML, cholangiocarcinoma, and, at our discretion, brain cancer indications.

Under the terms of the CStone Agreement, we received an initial upfront payment in the amount of $12.0 million and are entitled to receive up to an additional $412.0 million in milestone payments upon the achievement of certain development, regulatory and sales milestone events. Approximately half of the milestone payments are related to the development and commercialization of ivosidenib in AML, cholangiocarcinoma and the other half of the milestone payments are related to brain cancer indications, including glioma. We will also be entitled to receive tiered royalties, ranging from 15% to 19% percent, on annual net sales, if any, of ivosidenib.

CStone is responsible for all costs it incurs in developing, obtaining regulatory approval of, and commercializing ivosidenib in China, Hong Kong, Macau, and Taiwan, as well as certain costs incurred by us.

During the term of the CStone Agreement, each party and its affiliates are prohibited from developing or commercializing any other compound or product that inhibits IDH1 mutations at specified levels of binding, in the case of CStone, anywhere in the world, and in our case, in China, Hong Kong, Macau, and Taiwan.

Termination

Unless earlier terminated, the CStone Agreement will expire upon the expiration of the last royalty term for the last licensed product within the scope of the CStone Agreement. At any time after CStone has obtained regulatory approval in mainland China in R/R AML and the last patient has been enrolled in a specified clinical trial (or, if earlier, at any time that CStone acquires or is acquired by an entity with a competing or restricted product), CStone may terminate the CStone Agreement in its entirety by providing us with prior written notice. Either party may, subject to specified cure periods, terminate the CStone Agreement in the event of the other party’s uncured material breach. Either party may terminate the CStone Agreement under specified circumstances relating to the other party’s insolvency. We have the right to terminate the CStone Agreement immediately if CStone or its affiliates or sublicensees or subcontractors challenges the validity, patentability, or enforceability of certain patent rights that relate to ivosidenib and are owned by or licensed to us or our affiliates.

Accounting analysis and revenue recognition - collaboration revenue

The CStone Agreement was determined to be within the scope of ASC 606. Accordingly, in determining the appropriate amount of revenue to be recognized, we performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) we satisfied each performance obligation.

As part of the accounting for the CStone Agreement, we developed assumptions that require judgment to determine the SSP for each performance obligation identified in the contract. We use key assumptions to determine the SSP, which include forecast of revenues, development timelines, reimbursement rates, discount rates and probabilities of technical and regulatory success.

The satisfied and unsatisfied performance obligations, each of which are considered by us to be distinct within the context of the contract, their SSP, the method of recognizing the allocated consideration, and the period through which they are expected to be recognized are as follows:

Performance Obligations

SSP

No. of Performance
Obligation(s)

Recognition Method

License (1)

$16.4 million

Fully satisfied; recognized upon execution of CStone Agreement

Development service (2)

$1.7 million

Proportionally as services are delivered over the performance period, expected to be through September 2020 (3)

(1) The SSP was developed by probability weighting multiple cash flow scenarios using the income approach. Our management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimate of the direct costs incurred to generate future cash flows, a discount rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the SSP of these units of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals, and other factors. If different reasonable assumptions are utilized, the SSP and revenue recognized would vary.

(2) The SSP was developed using our management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider.

During the three and nine months ended September 30, 2018, we recognized as collaboration revenue the following non-contingent consideration allocated to each performance obligation (in thousands):


	September 30, 2018
	Three Months Ended										Nine Months Ended
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Collaboration revenue - other
License	$	—	$	—	$	—	$	12,440	$	12,000	$	440

The following table presents changes in our contract assets during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Collaboration receivable - other	$	—	$	12,440	$	(12,000)	$	440

(1) Additions to contract assets relate to amounts receivable from CStone. Deductions to contract assets relate to collection of receivables during the reporting period.

As of September 30, 2018, the aggregate amount of the transaction price allocated to performance obligations that are partially unsatisfied was $1.3 million.

Accounting analysis and revenue recognition – royalty revenue

The license was determined to be the predominant item to which sales-based royalties and sales-based milestones relate. As the license was delivered in June 2018, we will recognize royalty revenue when the related sales occur. To date, no royalties have been received under the CStone Agreement.

Accounting analysis and revenue recognition - milestone revenue

No milestones were earned during the three and nine months ended September 30, 2018. The next potential milestone expected to be achieved under the CStone Agreement is the dosing of the first patient in a local study in a hematological indication in mainland China. Achievement of this event will result in milestone payments of $5.0 million under the CStone Agreement.

Aurigene Discovery Technologies Limited

In April 2017, we entered into a new global license agreement with Aurigene Discovery Technologies Limited, or Aurigene, to research, develop and commercialize small molecule inhibitors for dihydroorotate dehydrogenase, or DHODH, or the Aurigene Agreement.

Under the terms of the Aurigene Agreement, Aurigene will provide to us exclusive rights to its portfolio of novel small molecules for DHODH. Financial terms of the Aurigene Agreement include a $3.0 million upfront payment and potential future milestone payments of up to $17.0 million if we achieve certain development and regulatory milestones. The next potential milestone expected to be achieved under our collaboration agreement with Aurigene is the initiation of the first phase 1 clinical trial for AG-636, our DHODH inhibitor. Achievement of this event will result in milestone payments owed to Aurigene of $2.0 million.

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

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

Accounting analysis

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

Share-Based Payments

9 Months Ended

Sep. 30, 2018

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

Share-Based Payments

2013 Stock Incentive Plan

In June 2013, our Board of Directors adopted and, in July 2013 our stockholders approved, the 2013 Stock Incentive Plan, or the 2013 Plan. The 2013 Plan became effective upon the closing of our initial public offering and provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units, or RSUs, performance-based stock units, or PSUs, and other stock-based awards. Following the adoption of the 2013 Plan, we granted no further stock options or other awards under the 2007 Stock Incentive Plan, or the 2007 Plan. Any options or awards outstanding under the 2007 Plan at the time of adoption of the 2013 Plan remained outstanding and effective. As of September 30, 2018, the total number of shares reserved under the 2007 Plan and the 2013 Plan are 8,024,444, and we had 1,918,363 shares available for future issuance under the 2013 Plan.

Stock options

The following table presents stock option activity for the nine months ended September 30, 2018:


	Number of Stock Options	Weighted-Average Exercise Price
Outstanding at December 31, 2017	5,577,562	$	49.58
Granted	1,293,020	78.35
Exercised	(1,078,290)	24.13
Forfeited/Expired	(306,978)	76.15
Outstanding at September 30, 2018	5,485,314	$	59.88
Exercisable at September 30, 2018	2,774,270	$	54.67
Vested and expected to vest at September 30, 2018	5,485,314	$	59.88

At September 30, 2018, the total unrecognized compensation expense related to unvested stock option awards was $107.4 million, which we expect to recognize over a weighted-average period of approximately 2.7 years.

Restricted stock units

The following table presents RSU activity for the nine months ended September 30, 2018:


	Number of Stock Units	Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2017	125,584	$	47.46
Granted	409,896	78.89
Vested	(57,250)	41.76
Forfeited	(24,494)	70.89
Unvested shares at September 30, 2018	453,736	$	75.31

As of September 30, 2018, there was approximately $25.1 million of total unrecognized compensation expense related to RSUs, which we expect to be recognized over a weighted-average period of approximately 2.1 years.

Performance-based stock units

The following table presents PSU activity for the nine months ended September 30, 2018:


	Number of Stock Units	Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2017	176,186	$	52.98
Granted	—	—
Vested	—	—
Forfeited	(9,155)	64.44
Unvested shares at September 30, 2018	167,031	$	52.36

As of September 30, 2018, there was approximately $1.1 million of total unrecognized compensation expense related to PSUs, which we expect to be recognized over a weighted-average period of approximately 0.3 years.

2013 Employee Stock Purchase Plan

In June 2013, our Board of Directors adopted, and in July 2013 our stockholders approved, the 2013 Employee Stock Purchase Plan, or the 2013 ESPP. We issued 53,255 shares and 59,651 shares during the nine months ended September 30, 2018 and 2017, respectively, under the 2013 ESPP. The 2013 ESPP provides participating employees with the opportunity to purchase up to an aggregate of 327,272 shares of our common stock. As of September 30, 2018, we had 160,536 shares available for future issuance under the 2013 ESPP.

Stock-based compensation expense

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	12,953	$	11,330	$	38,736	$	32,315
Restricted stock units	3,338		634		7,940		2,104
Performance-based stock units	7,656		—		7,656		—
Employee stock purchase plan	246		243		838		709
Total stock-based compensation expense	$	24,193	$	12,207	$	55,170	$	35,128

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Research and development expense	$	13,399	$	7,620	$	31,706	$	22,835
Sales, general and administrative expense	10,794		4,587		23,464		12,293
Total stock-based compensation expense	$	24,193	$	12,207	$	55,170	$	35,128

Loss per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Loss per Share

Basic net loss per share is calculated by dividing net loss by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting the weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method. For purposes of the dilutive net loss per share calculation, stock options, RSUs, PSUs for which the performance vesting conditions have been met, and ESPP options are considered to be common stock equivalents.

Since we had a net loss for all periods presented, the effect of all potentially dilutive securities is anti-dilutive. Accordingly, basic and diluted net loss per share was the same for all periods presented.

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


	Three and Nine Months Ended September 30,
	2018	2017
Stock options	5,485,314	5,820,611
Restricted stock units	453,736	120,000
Performance-based stock units	167,031	—
Employee stock purchase plan	5,332	5,348
Total common stock equivalents	6,111,413	5,945,959

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The condensed consolidated balance sheet as of September 30, 2018, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017 are unaudited. The unaudited condensed consolidated financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of our management, reflect all adjustments, which include only normal recurring adjustments, necessary to fairly state our financial position as of September 30, 2018, our results of operations for the three and nine months ended September 30, 2018 and 2017, and cash flows for the nine months ended September 30, 2018 and 2017. The financial data and the other financial information disclosed in these notes to the condensed consolidated financial statements related to the three and nine-month period are also unaudited. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the year ending December 31, 2018 or for any other future annual or interim period. The year-end condensed consolidated balance sheet data was derived from our audited financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles, or U.S. GAAP. Accordingly, the condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2017 that was filed with the Securities and Exchange Commission, or the SEC, on February 14, 2018. Our condensed 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 condensed consolidated financial statements have been prepared in conformity with U.S. GAAP.
Accounts receivable, net	Accounts receivable, net Our trade accounts receivable arise from product sales and represent amounts due from specialty distributors and specialty pharmacy providers in the U.S. We monitor the financial performance and creditworthiness of our customers so that we can properly assess and respond to changes in their credit profile. We reserve against these receivables for estimated losses that may arise from a customer’s inability to pay. Amounts determined to be uncollectible are charged or written-off against the reserve.
Concentrations of credit risk	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 receivables, including trade receivables from our customers and collaboration and royalty receivables from Celgene Corporation, or Celgene, and CStone Pharmaceuticals, or CStone. Concentrations of credit risk with respect to receivables, which are typically unsecured, are somewhat mitigated due to the number of customers using our products. Our trade receivables arise from product sales in the U.S. and have standard payment terms that generally require payment within 30 to 60 days. We have evaluated the creditworthiness of our customers, including Celgene, and determined them to be creditworthy. To date we have not experienced any losses with respect to our receivables.
Inventory	Inventory Inventory is stated at the lower of cost or estimated net realizable value on a first-in, first-out basis. Prior to the regulatory approval of our product candidates, we incur expenses for the manufacture of drug product that could potentially be available to support the commercial launch of those products. Until the date at which regulatory approval has been received or is otherwise considered probable, we record all such costs as research and development expenses. Our wholly owned product, TIBSOVO® (ivosidenib), received approval from the U.S. Food and Drug Administration, or FDA, on July 20, 2018 for the treatment of adult patients with relapsed or refractory acute myeloid leukemia, or R/R AML, with susceptible isocitrate dehydrogenase 1, or IDH1, mutation as detected by an FDA-approved test, and we began to capitalize inventories of TIBSOVO® beginning on July 20, 2018. We perform an assessment of the recoverability of capitalized inventory during each reporting period and write down any excess and obsolete inventory to its estimated net realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded as a component of cost of sales in the condensed consolidated statements of operations. The determination of whether inventory costs will be realizable requires the use of estimates by management. If actual market conditions are less favorable than projected by management, additional write-downs of inventory may be required.
Cost of Sales	Cost of SalesCost of sales consists primarily of manufacturing costs of TIBSOVO®. Based on our policy to expense costs associated with the manufacturing of our products prior to regulatory approval, certain of the manufacturing costs associated with product shipments of TIBSOVO® recorded during the three and nine months ended September 30, 2018 were expensed prior to July 20, 2018 and, therefore, are not included in costs of sales during the current period.
Recent accounting pronouncements	Recent accounting pronouncements In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), which was codified as ASC 842, Leases, and amended through subsequent ASUs. We are in the process of reviewing our existing lease contracts and continue to evaluate the accounting implications of ASC 842. We will adopt the guidance effective January 1, 2019 using the modified retrospective transition approach and we expect to elect the package of practical expedients, both provided for under ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. The package of practical expedients allows us not to reassess whether contracts are or contain leases, lease classification, and whether initial direct costs qualify for capitalization. Other accounting standards that have been issued by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on our financial statements upon adoption.
Fair Value Measurements	We record cash equivalents and marketable securities at fair value. ASC 820, Fair Value Measurements and Disclosures, establishes a fair value hierarchy for those instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and our own assumptions (unobservable inputs). The hierarchy consists of three levels: Level 1 – Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 – Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, directly or indirectly, for substantially the full term of the asset or liability. Level 3 – Unobservable inputs that reflect our own assumptions about the assumptions market participants would use in pricing the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.
Marketable Securities	Our marketable securities are classified as available-for-sale pursuant to ASC 320, Investments – Debt and Equity Securities, and are recorded at fair value, with unrealized gains and losses included as a component of accumulated other comprehensive loss in stockholders’ equity and a component of total comprehensive loss in the condensed consolidated statements of comprehensive loss, until realized. Realized gains and losses are included in investment income on a specific-identification basis.
Product Revenue	The performance obligation related to the sale of TIBSOVO® is satisfied and revenue is recognized when the Customer obtains control of the product, which occurs at a point in time, typically upon delivery to the Customer. Reserves for Variable Consideration Revenues from product sales are recorded at the net sales price, or transaction price, which includes estimates of variable consideration for which reserves are established and result from contractual adjustments, government rebates, returns and other allowances that are offered within the contracts with our Customers, healthcare providers, payors and other indirect customers relating to the sale of our products. Contractual Adjustments We generally provide Customers with discounts, including prompt pay discounts, and allowances that are explicitly stated in the contracts and are recorded as a reduction of revenue in the period the related product revenue is recognized. In addition, we receive sales order management, data and distribution services from certain Customers. Chargebacks for fees and discounts represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to Customers who directly purchase the product from us. Customers charge us for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These reserves are estimated using the expected value method, based upon a range of possible outcomes that are probability-weighted for the estimated channel mix and are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue. Government Rebates Government rebates consist of Medicare, TriCare, and Medicaid rebates, which we estimate using the expected value method, based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue. For Medicare, we also estimate the number of patients in the prescription drug coverage gap for whom we will owe an additional liability under the Medicare Part D program. Returns We estimate the amount of product sales that may be returned by Customers and record this estimate as a reduction of revenue in the period the related product revenue is recognized. We currently estimate product return liabilities using the expected value method, based on available industry data, including our visibility into the inventory remaining in the distribution channel.
Collaboration Revenue	On January 1, 2018 we adopted ASC 606 under the modified retrospective method. Prior to January 1, 2018 we accounted for the Collaboration Agreements under ASC 605-25, Multiple Element Arrangements. Accounting under ASC 606 In adopting ASC 606, we applied the practical expedient that permits aggregating the effect of all contract modifications that occurred prior to January 1, 2018. No other practical expedients were used. Similar to the accounting under ASC 605-25, the 2016 Agreement was determined to be a modification of the 2010 Agreement and the AG-881 Agreements. In determining the appropriate amount of revenue to be recognized under ASC 606, we performed the following steps: (i) identified the promised goods or services in the contract; (ii) determined whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measured the transaction price, including the constraint on variable consideration; (iv) allocated the transaction price to the performance obligations; and (v) recognized revenue when (or as) we satisfied each performance obligation. As part of the accounting for these arrangements, we must develop assumptions that require judgment to determine the stand-alone selling price, or SSP, for each performance obligation identified in the contract. We use key assumptions to determine the SSP, which include forecast of revenues, development timelines, reimbursement rates for personnel costs, discount rates and probabilities of technical and regulatory success.
Loss per Share	Basic net loss per share is calculated by dividing net loss by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting the weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury stock method. For purposes of the dilutive net loss per share calculation, stock options, RSUs, PSUs for which the performance vesting conditions have been met, and ESPP options are considered to be common stock equivalents.

Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)

9 Months Ended

Sep. 30, 2018

Accounting Policies [Abstract]

Schedule of Impact of New Accounting Pronouncements


	December 31, 2017		Cumulative Effect		January 1, 2018
Deferred revenue – related party, current and net of current portions	$	163,640	$	(39,456)	$	124,184
Accumulated deficit	(798,061)		39,456		(758,605)

The following tables summarize the effects of adopting ASC 606 on our unaudited condensed consolidated financial statements (in thousands, except per share data):

Condensed Consolidated Balance Sheets


	September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change
Accounts receivable, net	$	2,631	$	2,631	$	—
Collaboration receivable – related party	3,395		3,395		—
Collaboration receivable – other	440		—		440
Total current assets	695,542		695,102		440
Total assets	929,079		928,639		440

Deferred revenue – related party	42,141		33,648		8,493
Total current liabilities	84,746		76,253		8,493
Deferred revenue, net of current portion – related party	66,294		107,714		(41,420)

Total liabilities	168,866		201,793		(32,927)
Accumulated deficit	(1,012,839)		(1,046,206)		33,367
Total stockholders’ equity	760,213		726,846		33,367
Total liabilities and stockholders’ equity	929,079		928,639		440

Condensed Consolidated Statements of Operations


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Product revenue, net	$	4,465	$	4,465	$	—	$	4,465	$	4,465	$	—
Collaboration revenue – related party	8,732		10,137		(1,405)		42,478		46,096		(3,618)
Collaboration revenue – other	—		—		—		12,440		12,000		440
Research and development expense	82,561		81,714		847		247,515		244,604		2,911
Total cost and expenses	114,360		113,513		847		330,497		327,586		2,911
Loss from operations	(99,162)		(96,910)		(2,252)		(266,123)		(260,034)		(6,089)
Net loss	(94,664)		(92,412)		(2,252)		(254,234)		(248,145)		(6,089)
Net loss per share – basic and diluted	(1.63)		(1.59)		(0.04)		(4.45)		(4.34)		(0.11)

Condensed Consolidated Statements of Comprehensive Loss


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Net loss	$	(94,664)	$	(92,412)	$	(2,252)	$	(254,234)	$	(248,145)	$	(6,089)
Comprehensive loss	(94,385)		(92,133)		(2,252)		(254,964)		(248,875)		(6,089)

Condensed Consolidated Statements of Cash Flows


	Nine Months Ended September 30, 2018
	Under Topic 606		Under Topic 605		Effect of Change
Net loss	$	(254,234)	$	(248,145)	$	(6,089)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable, net	(2,631)		(2,631)		—
Collaboration receivable – related party	(947)		(947)		—
Collaboration receivable – other	(440)		—		(440)
Deferred revenue – related party	(15,749)		(22,278)		6,529

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

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

The following table summarizes our cash equivalents and marketable securities measured at fair value on a recurring basis as of September 30, 2018 (in thousands):


	Level 1		Level 2		Level 3		Total
Cash equivalents	$	129,123	$	24,001	$	—	$	153,124
Marketable securities:
Certificates of deposit	—		954		—		954
U.S. Treasuries	—		266,119		—		266,119
Government securities	—		114,407		—		114,407
Corporate debt securities	—		340,442		—		340,442
Total cash equivalents and marketable securities	$	129,123	$	745,923	$	—	$	875,046

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

Marketable securities at September 30, 2018 consisted of the following (in thousands):


	Amortized Cost		Unrealized Gains		Unrealized Losses		Fair Value
Current:
Certificates of deposit	$	960	$	—	$	(6)	$	954
U.S Treasuries	244,818		—		(302)		244,516
Government securities	61,522		—		(163)		61,359
Corporate debt securities	206,948		—		(363)		206,585
Non-current:
Certificates of deposit	—		—		—		—
U.S Treasuries	21,860		—		(257)		21,603
Government securities	53,301		—		(253)		53,048
Corporate debt securities	134,632		—		(775)		133,857
Total marketable securities	$	724,041	$	—	$	(2,119)	$	721,922

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
Total marketable securities	$	466,415	$	—	$	(1,389)	$	465,026

Inventory (Tables)

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventory consists of the following (in thousands):


	September 30, 2018
Raw materials	$	—
Work-in-process	788
Finished goods	75
Total Inventory	$	863

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2018

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consist of the following (in thousands):


	September 30, 2018		December 31, 2017
Accrued compensation	$	11,748	$	15,693
Accrued research and development costs	10,535		14,849
Accrued professional fees	2,509		3,140
Accrued other	511		349
Total accrued expenses	$	25,303	$	34,031

Product Revenue (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Schedule of Product Revenue Allowance and Reserves

The following table summarizes balances and activity in each of the product revenue allowance and reserve categories for the nine months ended September 30, 2018 (in thousands):


	Contractual Adjustments		Government Rebates		Returns		Total
Balance at December 31, 2017	$	—	$	—	$	—	$	—
Current provisions relating to sales in the current year	360		135		106		601

Payments/returns relating to sales in the current year	(180)		—		—		(180)

Balance at September 30, 2018	$	180	$	135	$	106	$	421

Schedule of Revenue Related Reserves

Total revenue-related reserves above, included in our condensed consolidated balance sheets, are summarized as follows (in thousands):


	September 30, 2018
Reduction of accounts receivable	$	98
Component of accrued expenses	323
Total revenue-related reserves	$	421

Schedule of Changes in Contract Assets and Liabilities, Product Revenue

The following table presents changes in our contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Accounts receivable, net	$	—	$	5,328	$	(2,697)	$	2,631

Collaboration and License Agreements (Tables)

9 Months Ended

Sep. 30, 2018

Revenue Recognition and Deferred Revenue [Abstract]

Schedule of Milestone-Based Payments Associated With 2016 Agreement

We are eligible to receive the following milestone-based payments associated with the 2016 Agreement:

Program

Milestone

Amount

65/35 program in IO field

Specified clinical development event

$25.0 million

65/35 program in IO field

Specified regulatory milestone events

Up to $183.8 million

50/50 program in IO field

Specified clinical development event

$20.0 million

50/50 program in IO field

Specified regulatory milestone events

Up to $148.8 million

I&I field

Specified clinical development event

$25.0 million

I&I field

Specified regulatory milestone events

Up to $236.3 million

I&I field

Specified commercial milestone events

Up to $125.0 million

Schedule of Satisfied and Unsatisfied Performance Obligations

Performance Obligations

SSP

No. of Performance Obligation(s)

Recognition Method

Fully satisfied at time of adoption

Licenses (1)

$86.7 million

Fully satisfied; recognized upon adoption of ASC 606

Research and development services (2)

$350.7 million

Fully satisfied; recognized upon adoption of ASC 606

Partially satisfied at time of adoption

Research and development services (2)

$266.6 million

Proportionally as services are delivered over the performance period, expected to be through September 2022 (3)

Schedule of Impact of New Accounting Pronouncements, Impact on Collaboration Revenue

During the three and nine months ended September 30, 2018, we recognized the following as collaboration revenue (in thousands):


	Three Months Ended September 30, 2018										Nine Months Ended September 30, 2018
Performance Obligation	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Collaboration revenue - related party
Licenses	$	—	$	—	$	—	$	15,000	$	15,000	$	—
Research and development services	7,504		8,864		(1,360)		23,698		27,184		(3,486)
Committee participation	—		45		(45)		—		132		(132)
Reduction of research and development expenses
Development services	—		847		(847)		—		2,911		(2,911)

Summary of Multiple-deliverable Arrangements Revenue, Allocated to Each Performance Obligation


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Licenses	$	—	$	—	$	15,000	$	—
On-going research and development services	7,504		9,708		23,698		30,374
Committee participation	—		41		—		124

Summary of Multiple-deliverable Arrangements Revenue

For the three and nine months ended September 30, 2018 and 2017, we recognized the following collaboration revenue and reduction of research and development expenses related to such expenses (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Collaboration revenue - related party
Development activities	$	312	$	—	$	902	$	—
Commercialization activities	916		894		2,878		1,999
Reduction of research and development expenses
Research and development activities	—		—		—		14

For the three and nine months ended September 30, 2018 and 2017, we recognized the following totals of collaboration revenue and reduction of research and development expenses (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Collaboration revenue - related party	$	8,732	$	10,643	$	42,478	$	32,497
Reduction of research and development expenses	—		1,078		—		6,343

Schedule of Changes in Contract Assets and Liabilities

The following table presents changes in our contract assets and liabilities during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Collaboration receivable – related party	$	2,448	$	26,233	$	(25,286)	$	3,395
Royalty receivable – related party	1,222		4,853		(4,212)		1,863
Contract liabilities (2)
Deferred revenue – related party, current and net of current portions	163,640		7,976		(63,181)		108,435

During the three and nine months ended September 30, 2018, we recognized the following as revenue due to changes in the contract liability balances (in thousands):


	September 30, 2018
	Three Months Ended		Nine Months Ended
Amounts included in the contract liability at the beginning of the period	$	7,555	$	23,472
Performance obligations satisfied in previous periods	219		762

Schedule of Royalty Revenue

During the three and nine months ended September 30, 2018 and 2017, we recognized the following as royalty revenue (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Royalty revenue – related party	$	2,001	$	715	$	4,991	$	715

Summary of Performance Obligations, CStone Agreement

Performance Obligations

SSP

No. of Performance
Obligation(s)

Recognition Method

License (1)

$16.4 million

Fully satisfied; recognized upon execution of CStone Agreement

Development service (2)

$1.7 million

Proportionally as services are delivered over the performance period, expected to be through September 2020 (3)

(1) The SSP was developed by probability weighting multiple cash flow scenarios using the income approach. Our management estimates within the models include the expected, probability-weighted net profits from estimated future sales, an estimate of the direct costs incurred to generate future cash flows, a discount rate and other business forecast factors. There are significant judgments and estimates inherent in the determination of the SSP of these units of accounting. These judgments and estimates include assumptions regarding future operating performance, the timelines of the clinical trials and regulatory approvals, and other factors. If different reasonable assumptions are utilized, the SSP and revenue recognized would vary.

(2) The SSP was developed using our management’s best estimate of the cost of obtaining these services at arm’s length from a third-party provider.

Summary of Multiple-deliverable Arrangements Revenue, Allocated to Each Performance Obligation, CStone Agreement

During the three and nine months ended September 30, 2018, we recognized as collaboration revenue the following non-contingent consideration allocated to each performance obligation (in thousands):


	September 30, 2018
	Three Months Ended										Nine Months Ended
	Under Topic 606		Under Topic 605		Effect of Change		Under Topic 606		Under Topic 605		Effect of Change
Collaboration revenue - other
License	$	—	$	—	$	—	$	12,440	$	12,000	$	440

Schedule of Changes in Contract Assets and Liabilities, CStone Agreement

The following table presents changes in our contract assets during the nine months ended September 30, 2018 (in thousands):


	December 31, 2017		Additions		Deductions		September 30, 2018
Contract assets (1)
Collaboration receivable - other	$	—	$	12,440	$	(12,000)	$	440

(1) Additions to contract assets relate to amounts receivable from CStone. Deductions to contract assets relate to collection of receivables during the reporting period.

Share-Based Payments (Tables)

9 Months Ended

Sep. 30, 2018

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

Summary of Company's Stock Option Activity

The following table presents stock option activity for the nine months ended September 30, 2018:


	Number of Stock Options	Weighted-Average Exercise Price
Outstanding at December 31, 2017	5,577,562	$	49.58
Granted	1,293,020	78.35
Exercised	(1,078,290)	24.13
Forfeited/Expired	(306,978)	76.15
Outstanding at September 30, 2018	5,485,314	$	59.88
Exercisable at September 30, 2018	2,774,270	$	54.67
Vested and expected to vest at September 30, 2018	5,485,314	$	59.88

Unvested Stock Unit Activity

The following table presents RSU activity for the nine months ended September 30, 2018:


	Number of Stock Units	Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2017	125,584	$	47.46
Granted	409,896	78.89
Vested	(57,250)	41.76
Forfeited	(24,494)	70.89
Unvested shares at September 30, 2018	453,736	$	75.31

Schedule of Performance-Based Units

The following table presents PSU activity for the nine months ended September 30, 2018:


	Number of Stock Units	Weighted-Average Grant Date Fair Value
Unvested shares at December 31, 2017	176,186	$	52.98
Granted	—	—
Vested	—	—
Forfeited	(9,155)	64.44
Unvested shares at September 30, 2018	167,031	$	52.36

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

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Stock options	$	12,953	$	11,330	$	38,736	$	32,315
Restricted stock units	3,338		634		7,940		2,104
Performance-based stock units	7,656		—		7,656		—
Employee stock purchase plan	246		243		838		709
Total stock-based compensation expense	$	24,193	$	12,207	$	55,170	$	35,128

Summary of Allocated Stock-Based Compensation Expense

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


	Three Months Ended September 30,						Nine Months Ended September 30,
	2018		2017		2018		2017
Research and development expense	$	13,399	$	7,620	$	31,706	$	22,835
Sales, general and administrative expense	10,794		4,587		23,464		12,293
Total stock-based compensation expense	$	24,193	$	12,207	$	55,170	$	35,128

Loss per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Common Stock Excluded from Calculation of Diluted Earnings Per Share


	Three and Nine Months Ended September 30,
	2018	2017
Stock options	5,485,314	5,820,611
Restricted stock units	453,736	120,000
Performance-based stock units	167,031	—
Employee stock purchase plan	5,332	5,348
Total common stock equivalents	6,111,413	5,945,959

Overview and Basis of Presentation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended
	Jan. 31, 2018	Sep. 30, 2018	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of shares issued from public offering (in shares)	8,152,986
Offer price (in usd per share)	$ 67.00
Proceeds from public offering of common stock, net of commissions	$ 516,200	$ 516,206	$ 270,250
Cash, cash equivalents, and short-term investments		$ 878,400

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Impact of the Cumulative Effect of Accounting Changes Upon Adoption of ASC 606 (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions		$ 124,184
Accumulated deficit	$ (1,012,839)	(758,605)	$ (798,061)
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions			163,640
Accumulated deficit	(1,046,206)		$ (798,061)
Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue – related party, current and net of current portions		(39,456)
Accumulated deficit	$ 33,367	$ 39,456

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	$ 2,631		$ 0
Collaboration receivable – related party	3,395		2,448
Collaboration receivable – other	440		0
Total current assets	695,542		445,261
Total assets	929,079		614,397
Deferred revenue – related party	42,141		37,842
Total current liabilities	84,746		94,941
Deferred revenue, net of current portion – related party	66,294		125,798
Total liabilities	168,866		238,894
Accumulated deficit	(1,012,839)	$ (758,605)	(798,061)
Total stockholders' equity	760,213		375,503
Total liabilities and stockholders’ equity	929,079		614,397
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	2,631
Collaboration receivable – related party	3,395
Collaboration receivable – other	0
Total current assets	695,102
Total assets	928,639
Deferred revenue – related party	33,648
Total current liabilities	76,253
Deferred revenue, net of current portion – related party	107,714
Total liabilities	201,793
Accumulated deficit	(1,046,206)		$ (798,061)
Total stockholders' equity	726,846
Total liabilities and stockholders’ equity	928,639
Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable, net	0
Collaboration receivable – related party	0
Collaboration receivable – other	440
Total current assets	440
Total assets	440
Deferred revenue – related party	8,493
Total current liabilities	8,493
Deferred revenue, net of current portion – related party	(41,420)
Total liabilities	(32,927)
Accumulated deficit	33,367	$ 39,456
Total stockholders' equity	33,367
Total liabilities and stockholders’ equity	$ 440

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 15,198	$ 11,358	$ 64,374	$ 33,212
Research and development expense	82,561	72,917	247,515	215,465
Total costs and expenses	114,360	90,375	330,497	263,876
Loss from operations	(99,162)	(79,017)	(266,123)	(230,664)
Net loss	$ (94,664)	$ (77,137)	$ (254,234)	$ (226,385)
Net loss per share – basic and diluted (usd per share)	$ (1.63)	$ (1.59)	$ (4.45)	$ (4.94)
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Research and development expense	$ 81,714		$ 244,604
Total costs and expenses	113,513		327,586
Loss from operations	(96,910)		(260,034)
Net loss	$ (92,412)		$ (248,145)
Net loss per share – basic and diluted (usd per share)	$ (1.59)		$ (4.34)
Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Research and development expense	$ 847		$ 2,911
Total costs and expenses	847		2,911
Loss from operations	(2,252)		(6,089)
Net loss	$ (2,252)		$ (6,089)
Net loss per share – basic and diluted (usd per share)	$ (0.04)		$ (0.11)
Product revenue, net
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 4,465	$ 0	$ 4,465	$ 0
Product revenue, net \| Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	4,465		4,465
Product revenue, net \| Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	0		0
Collaboration revenue - related party
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	8,732	10,643	42,478	32,497
Collaboration revenue - related party \| Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	10,137		46,096
Collaboration revenue - related party \| Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	(1,405)		(3,618)
Collaboration revenue - other
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	0	$ 0	12,440	$ 0
Collaboration revenue - other \| Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	0		12,000
Collaboration revenue - other \| Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues	$ 0		$ 440

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (94,664)	$ (77,137)	$ (254,234)	$ (226,385)
Comprehensive loss	(94,385)	$ (77,002)	(254,964)	$ (226,587)
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(92,412)		(248,145)
Comprehensive loss	(92,133)		(248,875)
Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(2,252)		(6,089)
Comprehensive loss	$ (2,252)		$ (6,089)

Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Effects of Adopting ASC 606 on Unaudited Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (94,664)	$ (77,137)	$ (254,234)	$ (226,385)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable, net			(2,631)	0
Collaboration receivable – related party			(947)	1,397
Collaboration receivable – other			(440)	0
Deferred revenue – related party	(15,749)		(15,749)	$ (20,141)
Under Topic 605
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	(92,412)		(248,145)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable, net			(2,631)
Collaboration receivable – related party			(947)
Collaboration receivable – other			0
Deferred revenue – related party	(22,278)
Accounting Standards Update 2014-09 \| Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (2,252)		(6,089)
Adjustments to reconcile net loss to net cash used in operating activities:
Accounts receivable, net			0
Collaboration receivable – related party			0
Collaboration receivable – other			(440)
Deferred revenue – related party			$ 6,529

Fair Value Measurements - Cash Equivalents and Marketable Securities Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring $ in Thousands	Sep. 30, 2018 USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 153,124
Total cash equivalents and marketable securities	875,046
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	954
U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	266,119
Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	114,407
Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	340,442
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	129,123
Total cash equivalents and marketable securities	129,123
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	24,001
Total cash equivalents and marketable securities	745,923
Level 2 \| Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	954
Level 2 \| U.S. Treasuries
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	266,119
Level 2 \| Government securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	114,407
Level 2 \| Corporate debt securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Marketable securities	340,442
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)	Sep. 30, 2018 USD ($)
Fair Value, Measurements, Recurring \| Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets (liabilities)	$ 0

Marketable Securities - Additional Information (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) security
Schedule of Available-for-sale Securities [Line Items]
Realized gain (loss) on marketable securities	$ 0	$ 0	$ 0	$ 0
Reclassifications out of accumulated other comprehensive income	$ 0	$ 0	$ 0	$ 0
Established time period for liquidation			12 months
Debt securities in an unrealized loss position \| security	236		236		240
Aggregate fair value of debt securities in an unrealized loss position	$ 659,800,000		$ 659,800,000		$ 439,400,000
Maximum
Schedule of Available-for-sale Securities [Line Items]
Minimum maturity (in years)			1 year
Maximum maturity (in years)			2 years
Minimum
Schedule of Available-for-sale Securities [Line Items]
Minimum maturity (in years)			1 year

Marketable Securities - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 724,041	$ 466,415
Unrealized Gains	0	0
Unrealized Losses	(2,119)	(1,389)
Fair Value	721,922	465,026
Current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	960	8,081
Unrealized Gains	0	0
Unrealized Losses	(6)	(11)
Fair Value	954	8,070
Current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	244,818	113,852
Unrealized Gains	0	0
Unrealized Losses	(302)	(119)
Fair Value	244,516	113,733
Current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	61,522	44,421
Unrealized Gains	0	0
Unrealized Losses	(163)	(57)
Fair Value	61,359	44,364
Current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	206,948	155,222
Unrealized Gains	0	0
Unrealized Losses	(363)	(177)
Fair Value	206,585	155,045
Non-current: \| Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	0	960
Unrealized Gains	0	0
Unrealized Losses	0	(8)
Fair Value	0	952
Non-current: \| U.S. Treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,860	36,165
Unrealized Gains	0	0
Unrealized Losses	(257)	(311)
Fair Value	21,603	35,854
Non-current: \| Government securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,301	23,992
Unrealized Gains	0	0
Unrealized Losses	(253)	(182)
Fair Value	53,048	23,810
Non-current: \| Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	134,632	83,722
Unrealized Gains	0	0
Unrealized Losses	(775)	(524)
Fair Value	$ 133,857	$ 83,198

Inventory - Schedule of Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 0
Work-in-process	788
Finished goods	75
Total inventory	$ 863	$ 0

Inventory - Additional Information (Details)	3 Months Ended
Inventory - Additional Information (Details)	Sep. 30, 2018 USD ($)
Inventory Disclosure [Abstract]
Inventory write-downs	$ 0

Accrued Expenses - Summary of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued compensation	$ 11,748	$ 15,693
Accrued research and development costs	10,535	14,849
Accrued professional fees	2,509	3,140
Accrued other	511	349
Total accrued expenses	$ 25,303	$ 34,031

Product Revenue - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 15,198	$ 11,358	$ 64,374	$ 33,212
Product revenue, net
Disaggregation of Revenue [Line Items]
Revenues	$ 4,465	$ 0	$ 4,465	$ 0

Product Revenue - Schedule of Product Revenue Allowance and Reserves (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Contractual Adjustments [Roll Forward]
Contract adjustments, beginning balance	$ 0
Contractual adjustments, current provisions relating to sales in the current year	360
Contractual adjustments, payments/returns relating to sales in the current year	(180)
Contract adjustments, ending balance	180
Government Rebates [Roll Forward]
Government rebates, beginning balance	0
Government rebates, current provisions relating to sales in the current year	135
Government rebates, payments/returns relating to sales in the current year	0
Government rebates, ending balance	135
Product Returns [Roll Forward]
Return reserve, beginning balance	0
Returns, current provisions relating to sales in the current year	106
Returns, payments/returns relating to sales in the current year	0
Return reserve, ending balance	106
Allowance for Doubtful Accounts Receivable [Roll Forward]
Total allowances and reserves, beginning balance	0
Total allowances and reserves, current provisions relating to sales in the current year	601
Total allowances and reserves, payments/returns relating to sales in the current year	(180)
Total allowances and reserves, ending balance	$ 421

Product Revenue - Schedule of Revenue-Related Reserves (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Reduction of accounts receivable	$ 98
Component of accrued expenses	323
Total revenue-related reserves	$ 421	$ 0

Product Revenue - Schedule of Changes in Contract Assets and Liabilities, Product Revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Contract assets
Contract assets, beginning balance	$ 0
Additions	5,328
Deductions	(2,697)
Contract assets, ending balance	$ 2,631

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

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

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

Collaboration and License 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 and License Agreements - AG-881 Agreements (Details)	Sep. 30, 2018 USD ($)
AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment for filing of first NDA	$ 35,000,000.0

Collaboration and License Agreements - 2010 Agreement (Details) - 2010 Agreement $ in Millions	Sep. 30, 2018 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone-based receivable payments, eligible to be received	$ 80.0
Milestone payments upon achievement of specified regulatory milestone events	55.0
Milestone payment upon achievement of a specified commercial milestone event	$ 25.0

Collaboration and License Agreements - Schedule of Satisfied and Unsatisfied Performance Obligations (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($) performance_obligation
Licenses \| Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $	$ 86.7
No. of Performance Obligation(s) \| performance_obligation	4
Research services \| Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $	$ 350.7
No. of Performance Obligation(s) \| performance_obligation	10
Research services \| Transferred over Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $	$ 266.6
No. of Performance Obligation(s) \| performance_obligation	6

Collaboration and License Agreements - Schedule of Effect of Adopting ASC 606 by Performance Obligation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	$ 8,732	$ 10,643	$ 42,478	$ 32,497
Reduction of research and development expenses	0	$ 1,078	0	$ 6,343
Licenses
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	0		15,000
Licenses \| Under Topic 605 \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	0		15,000
Licenses \| Effect of Change \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	0		0
Research services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	7,504		23,698
Research services \| Under Topic 605 \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	8,864		27,184
Research services \| Effect of Change \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	(1,360)		(3,486)
Committee participation
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	0		0
Committee participation \| Under Topic 605 \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	45		132
Committee participation \| Effect of Change \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Collaboration revenue – related party	(45)		(132)
Development services
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	0		0
Development services \| Under Topic 605 \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	847		2,911
Development services \| Effect of Change \| Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Reduction of research and development expenses	$ (847)		$ (2,911)

Collaboration and License Agreements - Summary of Collaboration Revenue Following Non-Contingent Consideration Allocated to Each Performance Obligation (Details) - Collaborative arrangement, product - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 0	$ 0	$ 15,000	$ 0
Research services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	7,504	9,708	23,698	30,374
Committee participation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 0	$ 41	$ 0	$ 124

Collaboration and License Agreements - Development and Commercialization Expense Not Contemplated As Part Of Modifications (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 8,732	$ 10,643	$ 42,478	$ 32,497
Reduction of research and development expenses	0	1,078	0	6,343
Development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction of research and development expenses	0		0
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	312	0	902	0
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Commercialization activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	916	894	2,878	1,999
Collaborative arrangement, product \| Not Included In Modification Due To High Level Of Uncertainty \| Research and development activities
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reduction of research and development expenses	$ 0	$ 0	$ 0	$ 14

Collaboration and License Agreements - Collaboration Revenue and Research and Development Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition and Deferred Revenue [Abstract]
Collaboration revenue – related party	$ 8,732	$ 10,643	$ 42,478	$ 32,497
Reduction of research and development expenses	$ 0	$ 1,078	$ 0	$ 6,343

Collaboration and License Agreements - Schedule of Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Contract assets
Contract assets, beginning balance		$ 0
Additions		5,328
Deductions		(2,697)
Contract assets, ending balance	$ 2,631	2,631
Contract liabilities
Additions	7,555	23,472
Collaboration receivable – related party
Contract assets
Contract assets, beginning balance		2,448
Additions		26,233
Deductions		(25,286)
Contract assets, ending balance	3,395	3,395
Royalty receivable – related party
Contract assets
Contract assets, beginning balance		1,222
Additions		4,853
Deductions		(4,212)
Contract assets, ending balance	1,863	1,863
Deferred revenue – related party, current and net of current portions
Contract liabilities
Contract liabilities, beginning balance		163,640
Additions		7,976
Deductions		(63,181)
Contract liabilities, ending balance	$ 108,435	$ 108,435

Collaboration and License Agreements - Schedule of Revenues as a Result of Changes in Contract Asset and Contract Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Revenue Recognition and Deferred Revenue [Abstract]
Amounts included in the contract liability at the beginning of the period	$ 7,555	$ 23,472
Performance obligations satisfied in previous periods	$ 219	$ 762

Collaboration and License Agreements - Remaining Unsatisfied Performance Obligations (Details) $ in Millions	Sep. 30, 2018 USD ($)
Revenue Recognition and Deferred Revenue [Abstract]
Remaining unsatisfied performance obligation	$ 115.9

Collaboration and License Agreements - Accounting Analysis and Revenue Recognition - Royalty and Milestone Revenue (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues	$ 15,198,000	$ 11,358,000	$ 64,374,000	$ 33,212,000
Milestones achieved	0	0	0	0
2010 Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment for filing of first NDA					$ 15,000,000.0
AG-881 program licenses
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment for filing of first NDA	35,000,000.0		35,000,000.0
Royalty revenue - related party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues	$ 2,001,000	$ 715,000	$ 4,991,000	$ 715,000

Collaboration and License Agreements - CStone Pharmaceuticals Purchase Agreement (Details) - CStone Pharmaceuticals - CStone Agreement - USD ($) $ in Thousands	1 Months Ended
	Jun. 30, 2018	Sep. 30, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 12,000
Potential future milestone payments		$ 412,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty percentage	15.00%
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty percentage	19.00%

Collaboration and License Agreements - Satisfied and Unsatisfied Performance Obligations Under CStone Agreement (Details) $ in Millions	1 Months Ended	9 Months Ended
	Jun. 30, 2018 USD ($) performance_obligation	Sep. 30, 2018 USD ($) performance_obligation
Licenses \| Transferred at Point in Time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $		$ 86.7
No. of Performance Obligation(s) \| performance_obligation		4
Licenses \| Transferred at Point in Time \| CStone Agreement
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $	$ 16.4
No. of Performance Obligation(s) \| performance_obligation	1
Development services \| Transferred over Time \| CStone Agreement
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Stand-alone selling price \| $	$ 1.7
No. of Performance Obligation(s) \| performance_obligation	1

Collaboration and License Agreements - Collaboration Revenue for Non-Contingent Consideration Allocation to Undelivered Element Under CStone Agreement (Details) - Licenses - CStone Agreement - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 0	$ 12,440
Accounting Standards Update 2014-09 \| Under Topic 605
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	0	12,000
Accounting Standards Update 2014-09 \| Effect of Change
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue – related party	$ 0	$ 440

Collaboration and License Agreements - Changes in Contract Assets and Liabilities Under CStone Agreement (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($)
Contract assets
Contract assets, beginning balance	$ 0
Additions	5,328
Deductions	(2,697)
Contract assets, ending balance	2,631
Collaboration receivable – related party
Contract assets
Contract assets, beginning balance	2,448
Additions	26,233
Deductions	(25,286)
Contract assets, ending balance	3,395
Collaboration receivable – related party \| CStone Agreement
Contract assets
Contract assets, beginning balance	0
Additions	12,440
Deductions	(12,000)
Contract assets, ending balance	$ 440

Collaboration and License Agreements - Performance Obligation Revenue and Royalty and Milestone Revenue Under CStone Agreement (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue Recognition and Deferred Revenue [Abstract]
Revenue from remaining performance obligations under CStone Agreement		$ 1,300,000		$ 1,300,000
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		15,198,000	$ 11,358,000	64,374,000	$ 33,212,000
Milestones achieved		0	0	0	0
CStone Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestones achieved		0		0
Milestone payment for dosing of first patient		5,000,000.0		5,000,000.0
Royalty revenue - related party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues		$ 2,001,000	$ 715,000	$ 4,991,000	$ 715,000
Royalty revenue - related party \| CStone Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues	$ 0

Collaboration and License Agreements - Aurigene Discovery Technologies Limited (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Apr. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment		$ 82,561	$ 72,917	$ 247,515	$ 215,465
Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 3,000
Potential future milestone payments						$ 17,000
DHODH Phase One Clinical Trial \| Aurigene Discovery Technologies Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone payments		$ 2,000		$ 2,000

Share-Based Payments - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense expected to be recognized	$ 24,193	$ 12,207	$ 55,170	$ 35,128
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	25,100		25,100
Compensation expense expected to be recognized	3,338	634	$ 7,940	2,104
Weighted-average period to recognize compensation expense (in years)			2 years 1 month 6 days
Performance-Based Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense expected to be recognized	$ 7,656	$ 0	$ 7,656	$ 0
Weighted-average period to recognize compensation expense (in years)			3 months 18 days
2007 Plan and 2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)	8,024,444		8,024,444
Shares available for future issuance (in shares)	1,918,363		1,918,363
2013 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 107,400		$ 107,400
Weighted-average period to recognize compensation expense (in years)			2 years 8 months 12 days
2013 Stock Incentive Plan \| Performance-Based Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation expense related to stock option	$ 1,100		$ 1,100
2013 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future issuance (in shares)	160,536		160,536
Shares issued under 2013 ESPP (in shares)			53,255	59,651
Opportunity to purchase of common stock (in shares)			327,272

Share-Based Payments - Summary of Company's Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Stock Options, Outstanding, Beginning balance (in shares) \| shares	5,577,562
Number of Stock Options, Granted (in shares) \| shares	1,293,020
Number of Stock Options, Exercised (in shares) \| shares	(1,078,290)
Number of Stock Options, Forfeited/Expired (in shares) \| shares	(306,978)
Number of Stock Options, Outstanding, Ending balance (in shares) \| shares	5,485,314
Number of Stock Options, Exercisable (in shares) \| shares	2,774,270
Number of Stock Options, Vested and expected to vest (in shares) \| shares	5,485,314
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, Beginning balance (in usd per share) \| $ / shares	$ 49.58
Weighted-Average Exercise Price, Granted (in usd per share) \| $ / shares	78.35
Weighted-Average Exercise Price, Exercised (in usd per share) \| $ / shares	24.13
Weighted-Average Exercise Price, Forfeited/Expired (in usd per share) \| $ / shares	76.15
Weighted-Average Exercise Price, Outstanding, Ending balance (in usd per share) \| $ / shares	59.88
Weighted-Average Exercise Price, Exercisable (in usd per share) \| $ / shares	54.67
Weighted-Average Exercise Price, Vested and expected to vest (in usd per share) \| $ / shares	$ 59.88

Share-Based Payments - Summary of Unvested RSUs Activity (Details) - Restricted stock units	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares beginning of period (in shares) \| shares	125,584
Granted (in shares) \| shares	409,896
Vested (in shares) \| shares	(57,250)
Forfeited/expired (in shares) \| shares	(24,494)
Unvested shares end of period (in shares) \| shares	453,736
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, Unvested shares beginning of period (in usd per share) \| $ / shares	$ 47.46
Weighted-average grant date fair value, Granted (in usd per share) \| $ / shares	78.89
Weighted-average grant date fair value, Vested (in usd per share) \| $ / shares	41.76
Weighted-average grant date fair value, Forfeited/expired (in usd per share) \| $ / shares	70.89
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) \| $ / shares	$ 75.31

Share-Based Payments - Schedule of Performance-Based Units (Details) - Performance-Based Stock Units (PSUs)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested shares beginning of period (in shares) \| shares	176,186
Granted (in shares) \| shares	0
Vested (in shares) \| shares	0
Forfeited/expired (in shares) \| shares	(9,155)
Unvested shares end of period (in shares) \| shares	167,031
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, Unvested shares beginning of period (in usd per share) \| $ / shares	$ 52.98
Weighted-average grant date fair value, Granted (in usd per share) \| $ / shares	0
Weighted-average grant date fair value, Vested (in usd per share) \| $ / shares	0
Weighted-average grant date fair value, Forfeited/expired (in usd per share) \| $ / shares	64.44
Weighted-average grant date fair value, Unvested shares end of period (in usd per share) \| $ / shares	$ 52.36

Share-Based Payments - Schedule of Stock-Based Compensation Expense by Award Type Included Within the Condensed Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 24,193	$ 12,207	$ 55,170	$ 35,128
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	12,953	11,330	38,736	32,315
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	3,338	634	7,940	2,104
Performance-Based Stock Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	7,656	0	7,656	0
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 246	$ 243	$ 838	$ 709

Share-Based Payments - Stock-Based Compensation Expense for Employee and Non-Employee Stock Options, Restricted Stock Units, Performance-Based Stock Options, Performance-Based Stock Units and Employee Stock Purchase Plan Shares (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 24,193	$ 12,207	$ 55,170	$ 35,128
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	13,399	7,620	31,706	22,835
Sales, general and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 10,794	$ 4,587	$ 23,464	$ 12,293

Loss per Share - Common Stock Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	6,111,413	5,945,959	6,111,413	5,945,959
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,485,314	5,820,611	5,485,314	5,820,611
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)	453,736	120,000	453,736	120,000
Performance-Based Stock Units (PSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	167,031	0	167,031	0
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (in shares)	5,332	5,348	5,332	5,348