Juno Therapeutics 10-Q 4 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	Apr. 27, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Trading Symbol	JUNO
Entity Registrant Name	Juno Therapeutics, Inc.
Entity Central Index Key	1,594,864
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		106,101,370

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 205,704	$ 187,891
Marketable securities	516,476	544,684
Accounts receivable	8,824	13,286
Prepaid expenses and other current assets	48,520	26,471
Total current assets	779,524	772,332
Property and equipment, net	102,517	81,734
Long-term marketable securities	128,472	189,706
Goodwill	221,306	221,306
Intangible assets	78,500	77,986
Other assets	4,345	6,400
Total assets	1,314,664	1,349,464
Current liabilities:
Accounts payable	3,206	4,415
Accrued liabilities and other current liabilities	45,357	36,822
Success payment liabilities	30,185	22,786
Contingent consideration	2,032	7,605
Deferred revenue	41,818	43,264
Total current liabilities	122,598	114,892
Contingent consideration, less current portion	19,316	13,291
Deferred revenue, less current portion	111,021	120,054
Deferred tax liabilities	4,864	5,152
Other long-term liabilities	40,813	18,374
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000 shares authorized; 0 shares issued and outstanding	0	0
Common stock, $0.0001 par value, 495,000 shares authorized at March 31, 2017 and December 31, 2016; 104,145 and 103,403 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	11	11
Additional paid-in-capital	1,930,138	1,911,769
Accumulated other comprehensive loss	(663)	(2,842)
Accumulated deficit	(913,434)	(831,237)
Total stockholders’ equity	1,016,052	1,077,701
Total liabilities and stockholders’ equity	$ 1,314,664	$ 1,349,464

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (shares)	5,000,000	5,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (shares)	$ 0.0001	$ 0.0001
Common stock, shares authorized (shares)	495,000,000	495,000,000
Common stock, shares issued (shares)	104,145,000	103,403,000
Common stock, shares outstanding (shares)	104,145,000	103,403,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Revenue	$ 19,327	$ 9,775
Operating expenses:
Research and development	82,924	73,722
General and administrative	20,726	15,954
Total operating expenses	103,650	89,676
Loss from operations	(84,323)	(79,901)
Interest income, net	1,700	1,341
Other income (expenses), net	(906)	69
Loss before income taxes	(83,529)	(78,491)
Benefit for income taxes	1,332	7,353
Net loss	$ (82,197)	$ (71,138)
Net loss per share, basic and diluted (in usd per share)	$ (0.79)	$ (0.72)
Weighted average common shares outstanding, basic and diluted (in shares)	103,752	99,298

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (82,197)	$ (71,138)
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustments	405	1,076
Net unrealized gain (loss) on marketable securities	1,774	107
Total other comprehensive income	2,179	1,183
Comprehensive loss	$ (80,018)	$ (69,955)

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
OPERATING ACTIVITIES
Net loss	$ (82,197)	$ (71,138)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,338	3,240
Non-cash stock-based compensation	16,439	13,005
Non-cash expense in connection with equity issuance	0	23,227
Deferred income taxes	(1,332)	(7,356)
Change in fair value of success payment liabilities	7,399	(6,583)
Change in fair value of contingent consideration	452	(1,012)
Other	915	0
Changes in operating assets and liabilities:
Accounts receivable	4,462	115
Prepaid expenses and other assets	(20,894)	(3,365)
Accounts payable, accrued liabilities and other liabilities	27,972	(4,455)
Deferred revenue	(10,482)	(3,843)
Net cash used in operating activities	(53,928)	(58,165)
INVESTING ACTIVITIES
Purchases of marketable securities and other investments	(104,799)	(150,519)
Sales and maturities of marketable securities	195,807	303,315
Acquisitions, net of cash acquired	0	(74,575)
Purchase of property and equipment	(21,152)	(4,036)
Net cash provided by investing activities	69,856	74,185
FINANCING ACTIVITIES
Proceeds from issuance of common stock to strategic partner	1,692	47,000
Proceeds from exercise of stock options, net of tax withholdings	238	679
Payments of build-to-suit lease obligation	0	(87)
Net cash provided by financing activities	1,930	47,592
Effect of exchange rate changes on cash and cash equivalents	(45)	(3)
Net increase in cash and cash equivalents	17,813	63,609
Cash and cash equivalents at beginning of period	187,891	252,398
Cash and cash equivalents at end of period	205,704	316,007
SUPPLEMENTAL CASH FLOW INFORMATION
Issuance of common stock for acquisitions	0	46,914
Issuance of common stock for success payments	$ 0	$ 9,481

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Organization and Basis of Presentation Juno Therapeutics, Inc. (the “Company”) was incorporated in Delaware on August 5, 2013 as FC Therapeutics, Inc., and changed its name to Juno Therapeutics, Inc. on October 23, 2013. The Company is building a fully-integrated biopharmaceutical company focused on developing innovative cellular immunotherapies for the treatment of cancer. Founded on the vision that the use of human cells as therapeutic entities will drive one of the next important phases in medicine, the Company is developing cell-based cancer immunotherapies based on its chimeric antigen receptor (“CAR”) and high-affinity T cell receptor (“TCR”) technologies to genetically engineer T cells to recognize and kill cancer cells. The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products, protection of proprietary technology, and the need to obtain adequate additional funding. If the Company, or any commercialization partner for the Company’s product candidates, does not successfully commercialize any of the Company’s product candidates, the Company will not be able to generate product revenue or achieve profitability. As of March 31, 2017 , the Company had an accumulated deficit of $913.4 million . The financial data as of December 31, 2016 is derived from the Company’s audited financial statements included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 1, 2017 (the “ 2016 Annual Report”), and should be read in conjunction with the audited financial statements and notes thereto. The Company’s significant accounting policies are described in Note 2 to the financial statements included in the 2016 Annual Report. These unaudited interim condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, consisting of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position, results of operations and comprehensive loss and cash flows for the interim periods. The results for the three months ended March 31, 2017 are not necessarily indicative of the results expected for the full fiscal year or any other interim period. Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from such estimates. See Note 2 to the audited financial statements included in the 2016 Annual Report for additional discussion of these estimates and assumptions. The Company utilizes significant estimates and assumptions in determining the estimated success payment and contingent consideration liabilities and associated expense or gain at each balance sheet date. A small change in the Company’s stock price may have a relatively large change in the estimated fair value of the success payment liability and associated expense or gain. Changes in the probabilities and estimated timing of milestones used in the calculation of the contingent consideration liability may have a relatively large impact on the resulting liability and associated expense or gain. Recent Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-09, Compensation—Stock Compensation (Topic 718) . The guidance was effective for reporting periods beginning after December 15, 2016, with early adoption permitted. The Company adopted this standard on January 1, 2017. The guidance required the Company to recognize all excess tax benefits previously unrecognized, along with any valuation allowance, on a modified retrospective basis as a cumulative-effect adjustment to accumulated deficit as of the date of adoption. As of January 1, 2017, the Company's deferred tax asset for net operating losses increased by $7.1 million but was offset by a full valuation allowance, so there was no impact to accumulated deficit on the condensed consolidated balance sheets. Additionally, the guidance required the Company to make a policy election to either estimate share-based payment forfeitures or recognize them as they occur, and apply the change from the policy election on a modified retrospective basis as a cumulative-effect adjustment to accumulated deficit as of the date of adoption. The Company elected to recognize forfeitures as they occur. Prior to the adoption of this guidance, the estimate for forfeitures was immaterial and as such there was no material impact to accumulated deficit on the condensed consolidated balance sheets upon adoption. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . The new guidance requires lessees to recognize the assets and liabilities arising from leases on the balance sheet and additional qualitative and quantitative disclosures will be required. The amendment is effective for reporting periods beginning after December 15, 2018, with early adoption permitted. The Company plans to adopt this standard on January 1, 2019 and is evaluating the impact of adopting the new accounting guidance on its consolidated financial statements. In 2014, the FASB issued ASU No. 2014-09, Revenue From Contracts With Customers (Topic 606) , amended by ASU No. 2015-14. This new standard will replace all current GAAP guidance on this topic and establishes principles for recognizing revenue upon the transfer of promised goods or services to customers, in an amount that reflects the expected consideration received in exchange for those goods or services. This guidance can be applied either retrospectively to each period presented or as a cumulative-effect adjustment as of the date of adoption. In 2015, the FASB voted to defer the effective date to reporting periods beginning after December 15, 2017, with early adoption permitted. The Company plans to adopt this standard on January 1, 2018. As of March 31, 2017, the majority of the Company's revenue is generated from upfront license payments, license milestone payments, and payments under its collaboration arrangement with Celgene Corporation and its wholly owned subsidiary Celgene Switzerland LLC (together, “Celgene”). The Company is currently evaluating the potential impact that Topic 606 may have on its consolidated financial statements.

Collaboration and License Agree

Collaboration and License Agreements	3 Months Ended
	Mar. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration and License Agreements	Collaboration and License Agreements See Note 5 of the financial statements included in the 2016 Annual Report for additional information related to the Company's collaboration and license agreements. Celgene The Company is party to a Master Research and Collaboration Agreement (“Celgene Collaboration Agreement”) with Celgene pursuant to which the Company and Celgene agreed to collaborate on researching, developing, and commercializing novel cellular therapy product candidates and other immuno-oncology and immunology therapeutics, including, in particular, CAR and TCR product candidates. In April 2016, Celgene exercised its opt-in right to develop and commercialize product candidates from the Company’s CD19 program outside North America and China. As a result, the Company and Celgene entered into a license agreement (the “Celgene CD19 License”) pursuant to which Celgene received an exclusive, royalty-bearing license to develop and commercialize therapeutic CAR product candidates from the Company’s CD19 program in all territories outside of North America and China. The Company is also party to a Share Purchase Agreement (the “Celgene Share Purchase Agreement”) with Celgene. In March 2017, Celgene exercised its annual right to purchase additional shares of the Company’s common stock to “top-up” its ownership interest in the Company. As Celgene did not exercise the top-up right in full in the first period to reach 10% ownership permitted by the top-up right, the top-up right that was triggered by the filing of the Company’s 2016 Annual Report only permitted Celgene to top-up its ownership stake in the Company to 9.76% . Celgene purchased 75,568 shares at a price of $22.39 per share, for an aggregate cash purchase price of $1.7 million , to top-up its ownership stake of the Company's common stock to the permitted amount of 9.76% . The top-up right that will be triggered by the filing of the Company’s Annual Report on Form 10-K for the fiscal year ending December 31, 2017 will again permit Celgene to top-up its ownership stake of the Company’s common stock to 9.76% . The Company recognized revenue of $19.1 million in the three months ended March 31, 2017 in connection with the Celgene Collaboration Agreement and the Celgene CD19 License. The Company recognized $3.8 million in revenue for the three months ended March 31, 2016 in connection with the Celgene Collaboration Agreement. Fred Hutchinson Cancer Research Center In October 2013, the Company entered into a collaboration agreement with the Fred Hutchinson Cancer Research Center (“FHCRC”) focused on research and development of cancer immunotherapy products and a license agreement pertaining to certain patent rights. The Company also granted FHCRC rights to certain share-based success payments. In December 2015, the Company entered into an agreement with FHCRC to support the establishment of a clinical immunotherapy trial unit. Excluding the expense or gain related to success payment obligations, the Company recognized $3.8 million and $4.5 million of research and development expenses in connection with its collaboration and funding agreements with FHCRC for the three months ended March 31, 2017 and 2016 , respectively. The estimated fair value of the total success payment obligation to FHCRC, after giving effect to the success payments achieved and paid in December 2015, was approximately $28.4 million and $22.9 million as of March 31, 2017 and December 31, 2016 , respectively. With respect to the FHCRC success payment obligations, the Company recognized an expense of $4.4 million compared to a gain of $4.7 million in the three months ended March 31, 2017 and 2016, respectively. The expense and gain are recorded in research and development expense in the condensed consolidated statements of operations, and represent the change in the FHCRC success payment liability during such periods and the respective months of accrued expenses. The FHCRC success payment liabilities on the condensed consolidated balance sheets as of March 31, 2017 and December 31, 2016 were $17.7 million and $13.3 million , respectively. The Company’s liability for share-based success payments under the FHCRC collaboration is carried at fair value and recognized as expense over the term of the six -year collaboration agreement. To determine the estimated fair value of the success payment liability, the Company uses a Monte Carlo simulation methodology which models the future movement of stock prices based on several key variables. The following variables were incorporated in the calculation of the estimated fair value of the success payment liability as of the following balance sheet dates: Assumptions March 31, 2017 December 31, 2016 Fair value of common stock $ 22.19 $ 18.85 Risk free interest rate 1.83% - 2.25% 1.88% - 2.30% Expected volatility 75% 75% Expected term (years) 4.54 - 7.55 4.79 - 7.79 The computation of expected volatility was estimated using a combination of available information about the historical volatility of stocks of similar publicly-traded companies for a period matching the expected term assumption and the Company’s historical and implied volatility. The risk free interest rate and expected term assumptions depend on the estimated timing of U.S. Food & Drug Administration (“FDA”) approval. In addition, the Company incorporated the estimated number and timing of valuation measurement dates in the calculation of the success payment liability. Memorial Sloan Kettering Cancer Center In November 2013, the Company entered into a sponsored research agreement with Memorial Sloan Kettering Cancer Center ("MSK") focused on research and development relating to CAR T cell technology and a license agreement pertaining to certain patent rights and intellectual property rights related to certain know-how. The Company also granted MSK rights to certain share-based success payments. The Company is also party to clinical study agreements with MSK. Excluding the expense or gain related to success payment obligations, the Company recognized $1.6 million and $0.7 million of research and development expenses in connection with its research and clinical agreements with MSK for the three months ended March 31, 2017 and 2016 , respectively. The estimated fair value of the total success payment obligation to MSK, after giving effect to the success payment achieved in December 2015 and paid in March 2016, was approximately $17.4 million and $14.1 million as of March 31, 2017 and December 31, 2016 , respectively. With respect to the MSK success payment obligations, the Company recognized an expense of $3.0 million compared to a gain of $1.9 million in the three months ended March 31, 2017 and 2016, respectively. The expense and gain are recorded in research and development expense in the condensed consolidated statements of operations, and represent the change in the MSK success payment liability during such periods and the respective months of accrued expense. The MSK success payment liabilities on the condensed consolidated balance sheets as of March 31, 2017 and December 31, 2016 were $12.5 million and $9.5 million , respectively. The Company’s liability for share-based success payments under the MSK collaboration is carried at fair value and recognized as expense over the term of the five-year collaboration agreement. To determine the estimated fair value of the success payment liability, the Company uses a Monte Carlo simulation methodology which models the future movement of stock prices based on several key variables. The following variables were incorporated in the calculation of the estimated fair value of the success payment liability as of the following balance sheet dates: Assumptions March 31, 2017 December 31, 2016 Fair value of common stock $ 22.19 $ 18.85 Risk free interest rate 1.85% – 2.26% 1.90% – 2.31% Expected volatility 75% 75% Expected term (years) 4.64 – 7.64 4.89 – 7.89 The computation of expected volatility was estimated using a combination of available information about the historical volatility of stocks of similar publicly-traded companies for a period matching the expected term assumption and the Company’s historical and implied volatility. The risk free interest rate and expected term assumptions depend on the estimated timing of FDA approval. In addition, the Company incorporated the estimated number and timing of valuation measurement dates in the calculation of the success payment liability.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2017
Cash and Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The following tables summarize the estimated fair value of cash equivalents and marketable securities and gross unrealized holding gains and losses (in thousands): March 31, 2017 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value Cash equivalents: Money market funds $ 169,007 $ — $ — $ 169,007 U.S. government and agency securities 10,495 1 — 10,496 Corporate debt securities 18,764 — (3 ) 18,761 Total cash equivalents $ 198,266 $ 1 $ (3 ) $ 198,264 Marketable securities: Commercial paper $ 21,193 $ — $ — $ 21,193 U.S. government and agency securities 326,269 2 (287 ) 325,984 Corporate debt securities 169,484 4 (189 ) 169,299 Total marketable securities $ 516,946 $ 6 $ (476 ) $ 516,476 Long-term marketable securities: U.S. government and agency securities $ 93,405 $ 1 $ (275 ) $ 93,131 Corporate debt securities 30,874 — (83 ) 30,791 Equity securities 1,700 2,850 — 4,550 Total long-term marketable securities $ 125,979 $ 2,851 $ (358 ) $ 128,472 December 31, 2016 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value Cash equivalents: Money market funds $ 173,746 $ — $ — $ 173,746 U.S. government and agency securities 4,712 — — 4,712 Corporate debt securities 6,334 — (6 ) 6,328 Total cash equivalents $ 184,792 $ — $ (6 ) $ 184,786 Marketable securities: Commercial paper $ 64,260 $ — $ — $ 64,260 U.S. government and agency securities 320,224 51 (68 ) 320,207 Corporate debt securities 160,379 18 (180 ) 160,217 Total marketable securities $ 544,863 $ 69 $ (248 ) $ 544,684 Long-term marketable securities: U.S. government and agency securities $ 132,622 $ 4 $ (364 ) $ 132,262 Corporate debt securities 55,920 1 (177 ) 55,744 Equity securities 1,700 — — 1,700 Total long-term marketable securities $ 190,242 $ 5 $ (541 ) $ 189,706 The following tables summarize the gross unrealized holding losses and fair value for investments in an unrealized loss position, and the length of time that individual securities have been in a continuous loss position (in thousands): March 31, 2017 Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Marketable securities: U.S. government and agency securities $ 289,772 $ (272 ) $ 9,985 $ (15 ) $ 299,757 $ (287 ) Corporate debt securities 140,500 (189 ) — — 140,500 (189 ) Total marketable securities $ 430,272 $ (461 ) $ 9,985 $ (15 ) $ 440,257 $ (476 ) Long-term marketable securities: U.S. government and agency securities $ 92,025 $ (275 ) $ — $ — $ 92,025 $ (275 ) Corporate debt securities 30,791 (83 ) — — 30,791 (83 ) Total long-term marketable securities $ 122,816 $ (358 ) $ — $ — $ 122,816 $ (358 ) December 31, 2016 Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Marketable securities: U.S. government and agency securities $ 143,480 $ (56 ) $ 9,988 $ (12 ) $ 153,468 $ (68 ) Corporate debt securities 128,013 (180 ) — — 128,013 (180 ) Total marketable securities $ 271,493 $ (236 ) $ 9,988 $ (12 ) $ 281,481 $ (248 ) Long-term marketable securities: U.S. government and agency securities $ 129,163 $ (364 ) $ — $ — $ 129,163 $ (364 ) Corporate debt securities 53,643 (177 ) — — 53,643 (177 ) Total long-term marketable securities $ 182,806 $ (541 ) $ — $ — $ 182,806 $ (541 ) The Company evaluated its securities for other-than-temporary impairment and considers the decline in market value for the securities to be primarily attributable to current economic and market conditions. For the debt securities, it is not more likely than not that the Company will be required to sell the securities, and the Company does not intend to do so prior to the recovery of the amortized cost basis. All marketable securities have an effective maturity date of three years or less and are available for use and therefore classified as available-for-sale.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The following tables set forth the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands): March 31, 2017 Level 1 Level 2 Level 3 Total Financial assets: Money market funds $ 169,007 $ — $ — $ 169,007 Commercial paper — 21,193 — 21,193 U.S. government and agency securities — 429,611 — 429,611 Corporate debt securities — 218,851 — 218,851 Equity securities 4,550 — — 4,550 Total financial assets $ 173,557 $ 669,655 $ — $ 843,212 Financial liabilities: Success payment liabilities $ — $ — $ 30,185 $ 30,185 Contingent consideration — — 21,348 21,348 Total financial liabilities $ — $ — $ 51,533 $ 51,533 December 31, 2016 Level 1 Level 2 Level 3 Total Financial assets: Money market funds $ 173,746 $ — $ — $ 173,746 Commercial paper — 64,260 — 64,260 U.S. government and agency securities — 457,181 — 457,181 Corporate debt securities — 222,289 — 222,289 Equity securities 1,700 — — 1,700 Total financial assets $ 175,446 $ 743,730 $ — $ 919,176 Financial liabilities: Success payment liabilities $ — $ — $ 22,786 $ 22,786 Contingent consideration — — 20,896 20,896 Total financial liabilities $ — $ — $ 43,682 $ 43,682 The Company measures the fair value of money market funds based on quoted prices in active markets for identical assets or liabilities. The Level 2 marketable securities include U.S. government and agency securities, corporate debt securities, and commercial paper and are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities (in thousands): Success Payment Liabilities Contingent Consideration Total Balance as of December 31, 2016 $ 22,786 $ 20,896 $ 43,682 Changes in fair value (1) 7,399 452 7,851 Balance as of March 31, 2017 $ 30,185 $ 21,348 $ 51,533 (1) The amount of success payment and contingent consideration milestones achieved, as well as the changes in fair value for success payment liabilities and contingent consideration, are recorded in research and development expense in the condensed consolidated statements of operations. As of March 31, 2017 and December 31, 2016 , the estimated fair value of the success payment obligations, after giving effect to the success payments achieved by FHCRC and MSK, was approximately $45.8 million and $37.0 million , respectively. Included in research and development expense for the three months ended March 31, 2017 and 2016 was an expense of $7.4 million and a gain of $6.6 million , respectively, related to success payments. See Note 2, Collaboration and License Agreements, to these condensed consolidated financial statements, as well as Note 5 to the financial statements included in the 2016 Annual Report, for additional discussion of estimated fair value of the success payment obligations. The Company utilizes significant estimates and assumptions in determining the estimated success payment liability and associated expense at each balance sheet date. The assumptions used to calculate the fair value of the success payments are subject to a significant amount of judgment including the expected volatility, estimated term, and estimated number and timing of valuation measurement dates. A small change in the assumptions and other inputs, such as the fair value of the Company's common stock, may have a relatively large change in the estimated valuation and associated liability and expense. For example, keeping all other variables constant, a hypothetical 10% increase in the stock price at March 31, 2017 from $22.19 per share to $24.41 per share would have increased the expense recorded in the first quarter of 2017 associated with the success payment liability by $4.1 million . A hypothetical 10% decrease in the stock price from $22.19 per share to $19.97 per share would have decreased the expense recorded in the first quarter of 2017 associated with the success payment liability by $4.0 million . Further, keeping all other variables constant, a hypothetical 35% increase in the stock price at March 31, 2017 from $22.19 per share to $29.96 per share would have increased the expense recorded in the first quarter of 2017 associated with the success payment liability by $14.5 million . A hypothetical 35% decrease in the stock price from $22.19 per share to $14.42 per share would have decreased the expense recorded in the first quarter of 2017 associated with the success payment liability to zero , resulting in a gain of $6.3 million . In connection with the acquisitions of Stage Cell Therapeutics GmbH (“Stage”) and X-Body, Inc. (“X-Body”) in the second quarter of 2015, the Company agreed to pay additional amounts based on the achievement of certain technical, clinical, regulatory, and commercialization milestones. This contingent consideration is measured at fair value and is based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The valuation of contingent consideration uses assumptions the Company believes would be made by a market participant. The Company assesses these estimates on an on-going basis as additional data impacting the assumptions is obtained. Contingent consideration may change significantly as development progresses and additional data are obtained, impacting the Company’s assumptions regarding probabilities of successful achievement of related milestones used to estimate the fair value of the liability and the timing in which they are expected to be achieved. In evaluating the fair value information, judgment is required to interpret the data used to develop the estimates. The estimates of fair value may not be indicative of the amounts that could be realized in a current market exchange. Accordingly, the use of different market assumptions and/or different valuation techniques could result in materially different fair value estimates. The significant unobservable inputs used in the measurement of fair value of the Company’s contingent consideration are probabilities of successful achievement of the milestones, the period in which these milestones are expected to be achieved ranging from 2017 to 2043 , and a discount rate of 16% . Significant increases or decreases in any of the probabilities of success and other inputs would result in a significantly higher or lower fair value measurement, respectively. As of March 31, 2017 , the estimated fair values of the contingent consideration associated with the Stage and X-Body acquisitions, after giving effect to the milestone achieved in 2016, were $17.9 million and $3.5 million , respectively. The Company recognized an expense of $0.4 million and a gain of $1.0 million related to the change in fair value of the contingent consideration in the three months ended March 31, 2017 and 2016 , respectively. The expense and gain are recorded in research and development expense in the condensed consolidated statement of operations.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation Stock-Based Compensation Stock-based compensation expense is recognized in the condensed consolidated statements of operations as follows (in thousands): Three Months Ended March 31, 2017 2016 Research and development (1) $ 10,329 $ 10,291 General and administrative 6,110 4,927 Total stock-based compensation expense (2) $ 16,439 $ 15,218 (1) Included in research and development stock-based compensation expense for the three months ended March 31, 2016 was $2.2 million related to the payout of employee stock options in connection with the AbVitro Inc. ("AbVitro") acquisition. (2) Included in stock-based compensation expense recognized for the three months ended March 31, 2017 and 2016 , is $1.0 million and $1.6 million , respectively, related to service providers other than employees, scientific founders, and directors, including $0.7 million and $1.2 million , respectively, for a former cofounding director who became a consultant upon his departure from the board of directors. Total stock-based compensation cost related to unvested awards not yet recognized and the weighted average periods over which the awards are expected to be recognized as of March 31, 2017 for all employees are as follows: Stock Options Restricted Stock Unrecognized stock-based compensation cost (in thousands) $ 142,691 $ 46,092 Expected weighted average period compensation costs to be recognized (years) 2.84 2.72 Restricted Stock and RSUs A summary of the Company’s restricted stock and RSU activity is as follows (in thousands, except per share data): Restricted Stock Weighted Average Fair Value at Date of Grant per Share Unvested shares as of December 31, 2016 3,055 $ 7.10 Granted 1,226 20.82 Vested (636 ) 1.67 Forfeited (18 ) 18.53 Unvested shares as of March 31, 2017 3,627 $ 12.66 Stock Options A summary of the Company’s stock option activity is as follows (in thousands, except per share and contractual life data): Stock Options Weighted Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Outstanding as of December 31, 2016 8,521 $ 30.28 Granted 2,550 20.70 Exercised (31 ) 7.67 Forfeited/Cancelled (115 ) 36.89 Outstanding as of March 31, 2017 10,925 $ 28.02 8.75 $ 31,888 Exercisable as of March 31, 2017 2,852 $ 29.61 7.98 $ 14,654 The fair value of each stock option granted has been determined using the Black-Scholes option pricing model. The material factors incorporated in the Black-Scholes model in estimating the fair value of the options granted to employees, directors, and consultants included the following: Assumptions Three Months Ended March 31, 2017 Risk free interest rate 1.96% – 2.40% Expected volatility 75% Expected life (years) 6.02 - 9.40 Expected dividend yield 0% For employees, scientific founders, and directors, the expected life was calculated based on the simplified method as permitted by the SEC Staff Accounting Bulletin No. 110, Share-Based Payment . For other service providers, the expected life was calculated using the contractual term of the award. Management’s estimate of expected volatility was based on available information about the historical volatility of stocks of similar publicly-traded companies for a period matching the expected term assumption and its own historical and implied future volatility. The risk-free interest rate is based on a U.S. Treasury instrument whose term is consistent with the expected life of the stock options. In addition to the assumptions above, management made an estimate of expected forfeitures and is recognizing compensation costs only for those equity awards expected to vest.

Comprehensive Income (Loss)

Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Comprehensive Income (Loss)	Comprehensive Income (Loss) The components of accumulated other comprehensive income (loss) and the adjustments to other comprehensive income (loss) are as follows (in thousands): Foreign Currency Translation Adjustments Net Unrealized Gain (Loss) on Marketable Securities Accumulated Other Comprehensive Income (Loss) Balance as of December 31, 2016 $ (1,791 ) $ (1,051 ) $ (2,842 ) Other comprehensive income 405 1,774 2,179 Balance as of March 31, 2017 $ (1,386 ) $ 723 $ (663 )

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company recorded an income tax benefit of $1.3 million on a pre-tax loss of $83.5 million for the three months ended March 31, 2017 . The income tax benefit primarily relates to the benefit associated with the net loss incurred by the Company’s German subsidiary in the three months ended March 31, 2017 . The Company recorded an income tax benefit of $7.4 million on a pre-tax loss of $78.5 million for the three months ended March 31, 2016 . Of the total tax benefit, $6.7 million relates to the release of valuation allowance on the U.S. deferred tax assets as a result of the deferred tax liabilities established for intangible assets from the acquisition of AbVitro, net of tax attributes, and $0.7 million relates to the benefit associated with the net loss incurred by the Company’s German subsidiary in the three months ended March 31, 2016 . The Company maintains a full valuation allowance on its net U.S. deferred tax assets. The assessment regarding whether a valuation allowance is required considers both positive and negative evidence when determining whether it is more-likely-than-not that deferred tax assets are recoverable. In making this assessment, significant weight is given to evidence that can be objectively verified. In its evaluation, the Company considered its cumulative loss in recent years and its forecasted losses in the near-term as significant negative evidence. Based upon a review of the four sources of income identified within Accounting Standard Codification ("ASC") 740, Accounting for Income Taxes , the Company determined that the negative evidence outweighed the positive evidence and a full valuation allowance on its U.S. net deferred tax assets will be maintained. The Company will continue to assess the realizability of its deferred tax assets going forward and will adjust the valuation allowance as needed. The Company has determined that it is more-likely-than-not that it will realize the benefit of the losses for its German subsidiary and has not recorded a valuation allowance against the German deferred tax assets. The Company is generally subject to examination by the U.S. federal and local income tax authorities for all tax years in which a loss carryforward is available and is subject to examination in Germany for four years. The Company's German subsidiary is currently under examination by the German tax authorities for the years ended December 31, 2013 through December 31, 2015. The Company applies judgment in the determination of the consolidated financial statement recognition and measurement of tax positions taken or expected to be taken in a tax return. As of March 31, 2017 and December 31, 2016 , the Company's uncertain tax positions were immaterial.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic and diluted net loss per share is calculated by dividing net loss by the weighted average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include unvested restricted stock, unvested RSUs, options to purchase common stock, and potential shares issued for success payments, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The amounts in the table below were excluded from the calculation of diluted net loss per share for the periods indicated due to their anti-dilutive effect (in thousands): Three Months Ended March 31, 2017 2016 Unvested restricted stock and RSUs 3,627 4,983 Options to purchase common stock 10,925 7,471 Total 14,552 12,454

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company has entered into various lease agreements for its office, laboratory, and manufacturing spaces with original lease periods expiring between 2017 and 2026 . In addition to minimum rent, certain leases require payment of real estate taxes, insurance, common area maintenance charges and other executory costs. These executory costs are not included in the table below. Certain of these arrangements have free or escalating rent payment provisions. The Company recognizes rent expense under such arrangements on a straight-line basis over the effective term of each lease. The following table summarizes the Company’s future minimum lease commitments as of March 31, 2017 (in thousands): Year ending December 31: 2017 $ 3,147 2018 11,498 2019 13,422 2020 13,568 2021 13,881 Thereafter 36,874 Total minimum lease payments $ 92,390 Rent expense for the three months ended March 31, 2017 and 2016 was $2.6 million and $1.1 million , respectively. Litigation From time to time, the Company may become involved in litigation or proceedings relating to claims arising from the ordinary course of business. Beginning on July 12, 2016, three putative securities class action complaints were filed against the Company and several of its officers. On October 7, 2016, these complaints were consolidated into a single action titled "In re Juno Therapeutics, Inc." On October 19, 2016, the Court appointed a lead plaintiff. On December 12, 2016, the lead plaintiff filed an amended complaint. The putative class in the amended complaint is composed of all purchasers of the Company’s securities between May 9, 2016 and November 22, 2016, inclusive. The amended complaint names as defendants the Company, its chief executive officer, its chief financial officer, and its chief medical officer and generally alleges material misrepresentations and omissions in public statements regarding patient deaths in the Company’s Phase II clinical trial of JCAR015 and the safety of JCAR015, violations by all named defendants of Section 10(b) of the Exchange Act, and Rule 10b-5 thereunder, as well as violations of Section 20(a) of the Exchange Act by the individual defendants. The amended complaint seeks compensatory damages of an undisclosed amount. On February 2, 2017, the Company and the individual defendants filed a motion to dismiss the complaint. On March 20, 2017, the plaintiffs filed an opposition to the motion to dismiss. On April 19, 2017, the Company and the individual defendants filed a reply in support of the motion to dismiss. The Company has not recorded any liability as of March 31, 2017 since any potential loss is not probable or reasonably estimable given the preliminary nature of the proceedings.

Related-Party Transactions

Related-Party Transactions	3 Months Ended
	Mar. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions The Company is party to the Celgene Collaboration Agreement, the Celgene CD19 License, the Celgene Share Purchase Agreement, a voting agreement, and a registration rights agreement with Celgene, who is a holder of more than 5% of the Company’s common stock. See Note 2, Collaboration and License Agreements, to these condensed consolidated financial statements, as well as Note 5 to the financial statements included in the 2016 Annual Report.

Significant Accounting Polici17

Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation Juno Therapeutics, Inc. (the “Company”) was incorporated in Delaware on August 5, 2013 as FC Therapeutics, Inc., and changed its name to Juno Therapeutics, Inc. on October 23, 2013. The Company is building a fully-integrated biopharmaceutical company focused on developing innovative cellular immunotherapies for the treatment of cancer. Founded on the vision that the use of human cells as therapeutic entities will drive one of the next important phases in medicine, the Company is developing cell-based cancer immunotherapies based on its chimeric antigen receptor (“CAR”) and high-affinity T cell receptor (“TCR”) technologies to genetically engineer T cells to recognize and kill cancer cells. The Company is subject to a number of risks similar to other biopharmaceutical companies in the early stage, including, but not limited to, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products, protection of proprietary technology, and the need to obtain adequate additional funding. If the Company, or any commercialization partner for the Company’s product candidates, does not successfully commercialize any of the Company’s product candidates, the Company will not be able to generate product revenue or achieve profitability. As of March 31, 2017 , the Company had an accumulated deficit of $913.4 million . The financial data as of December 31, 2016 is derived from the Company’s audited financial statements included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 1, 2017 (the “ 2016 Annual Report”), and should be read in conjunction with the audited financial statements and notes thereto. The Company’s significant accounting policies are described in Note 2 to the financial statements included in the 2016 Annual Report. These unaudited interim condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). In management’s opinion, the unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, consisting of normal recurring adjustments, necessary for the fair presentation of the Company’s financial position, results of operations and comprehensive loss and cash flows for the interim periods. The results for the three months ended March 31, 2017 are not necessarily indicative of the results expected for the full fiscal year or any other interim period.
Use of Estimates	Use of Estimates The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from such estimates. See Note 2 to the audited financial statements included in the 2016 Annual Report for additional discussion of these estimates and assumptions. The Company utilizes significant estimates and assumptions in determining the estimated success payment and contingent consideration liabilities and associated expense or gain at each balance sheet date. A small change in the Company’s stock price may have a relatively large change in the estimated fair value of the success payment liability and associated expense or gain. Changes in the probabilities and estimated timing of milestones used in the calculation of the contingent consideration liability may have a relatively large impact on the resulting liability and associated expense or gain.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-09, Compensation—Stock Compensation (Topic 718) . The guidance was effective for reporting periods beginning after December 15, 2016, with early adoption permitted. The Company adopted this standard on January 1, 2017. The guidance required the Company to recognize all excess tax benefits previously unrecognized, along with any valuation allowance, on a modified retrospective basis as a cumulative-effect adjustment to accumulated deficit as of the date of adoption. As of January 1, 2017, the Company's deferred tax asset for net operating losses increased by $7.1 million but was offset by a full valuation allowance, so there was no impact to accumulated deficit on the condensed consolidated balance sheets. Additionally, the guidance required the Company to make a policy election to either estimate share-based payment forfeitures or recognize them as they occur, and apply the change from the policy election on a modified retrospective basis as a cumulative-effect adjustment to accumulated deficit as of the date of adoption. The Company elected to recognize forfeitures as they occur. Prior to the adoption of this guidance, the estimate for forfeitures was immaterial and as such there was no material impact to accumulated deficit on the condensed consolidated balance sheets upon adoption. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) . The new guidance requires lessees to recognize the assets and liabilities arising from leases on the balance sheet and additional qualitative and quantitative disclosures will be required. The amendment is effective for reporting periods beginning after December 15, 2018, with early adoption permitted. The Company plans to adopt this standard on January 1, 2019 and is evaluating the impact of adopting the new accounting guidance on its consolidated financial statements. In 2014, the FASB issued ASU No. 2014-09, Revenue From Contracts With Customers (Topic 606) , amended by ASU No. 2015-14. This new standard will replace all current GAAP guidance on this topic and establishes principles for recognizing revenue upon the transfer of promised goods or services to customers, in an amount that reflects the expected consideration received in exchange for those goods or services. This guidance can be applied either retrospectively to each period presented or as a cumulative-effect adjustment as of the date of adoption. In 2015, the FASB voted to defer the effective date to reporting periods beginning after December 15, 2017, with early adoption permitted. The Company plans to adopt this standard on January 1, 2018. As of March 31, 2017, the majority of the Company's revenue is generated from upfront license payments, license milestone payments, and payments under its collaboration arrangement with Celgene Corporation and its wholly owned subsidiary Celgene Switzerland LLC (together, “Celgene”). The Company is currently evaluating the potential impact that Topic 606 may have on its consolidated financial statements.

Collaboration and License Agr18

Collaboration and License Agreements (Tables)	3 Months Ended
	Mar. 31, 2017
Fred Hutchinson Cancer Research Center
Related Party Transaction [Line Items]
Assumptions Used to Calculate Estimated Fair Value of Success Payment Liability	The following variables were incorporated in the calculation of the estimated fair value of the success payment liability as of the following balance sheet dates: Assumptions March 31, 2017 December 31, 2016 Fair value of common stock $ 22.19 $ 18.85 Risk free interest rate 1.83% - 2.25% 1.88% - 2.30% Expected volatility 75% 75% Expected term (years) 4.54 - 7.55 4.79 - 7.79
Memorial Sloan Kettering Cancer Center
Related Party Transaction [Line Items]
Assumptions Used to Calculate Estimated Fair Value of Success Payment Liability	The following variables were incorporated in the calculation of the estimated fair value of the success payment liability as of the following balance sheet dates: Assumptions March 31, 2017 December 31, 2016 Fair value of common stock $ 22.19 $ 18.85 Risk free interest rate 1.85% – 2.26% 1.90% – 2.31% Expected volatility 75% 75% Expected term (years) 4.64 – 7.64 4.89 – 7.89

Cash Equivalents and Marketab19

Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2017
Cash and Cash Equivalents [Abstract]
Summary of Estimated Fair Value of Cash Equivalents and Marketable Securities	The following tables summarize the estimated fair value of cash equivalents and marketable securities and gross unrealized holding gains and losses (in thousands): March 31, 2017 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value Cash equivalents: Money market funds $ 169,007 $ — $ — $ 169,007 U.S. government and agency securities 10,495 1 — 10,496 Corporate debt securities 18,764 — (3 ) 18,761 Total cash equivalents $ 198,266 $ 1 $ (3 ) $ 198,264 Marketable securities: Commercial paper $ 21,193 $ — $ — $ 21,193 U.S. government and agency securities 326,269 2 (287 ) 325,984 Corporate debt securities 169,484 4 (189 ) 169,299 Total marketable securities $ 516,946 $ 6 $ (476 ) $ 516,476 Long-term marketable securities: U.S. government and agency securities $ 93,405 $ 1 $ (275 ) $ 93,131 Corporate debt securities 30,874 — (83 ) 30,791 Equity securities 1,700 2,850 — 4,550 Total long-term marketable securities $ 125,979 $ 2,851 $ (358 ) $ 128,472 December 31, 2016 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value Cash equivalents: Money market funds $ 173,746 $ — $ — $ 173,746 U.S. government and agency securities 4,712 — — 4,712 Corporate debt securities 6,334 — (6 ) 6,328 Total cash equivalents $ 184,792 $ — $ (6 ) $ 184,786 Marketable securities: Commercial paper $ 64,260 $ — $ — $ 64,260 U.S. government and agency securities 320,224 51 (68 ) 320,207 Corporate debt securities 160,379 18 (180 ) 160,217 Total marketable securities $ 544,863 $ 69 $ (248 ) $ 544,684 Long-term marketable securities: U.S. government and agency securities $ 132,622 $ 4 $ (364 ) $ 132,262 Corporate debt securities 55,920 1 (177 ) 55,744 Equity securities 1,700 — — 1,700 Total long-term marketable securities $ 190,242 $ 5 $ (541 ) $ 189,706
Summary of Gross Unrealized Holding Losses and Fair Value for Investments in Unrealized Loss Position	The following tables summarize the gross unrealized holding losses and fair value for investments in an unrealized loss position, and the length of time that individual securities have been in a continuous loss position (in thousands): March 31, 2017 Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Marketable securities: U.S. government and agency securities $ 289,772 $ (272 ) $ 9,985 $ (15 ) $ 299,757 $ (287 ) Corporate debt securities 140,500 (189 ) — — 140,500 (189 ) Total marketable securities $ 430,272 $ (461 ) $ 9,985 $ (15 ) $ 440,257 $ (476 ) Long-term marketable securities: U.S. government and agency securities $ 92,025 $ (275 ) $ — $ — $ 92,025 $ (275 ) Corporate debt securities 30,791 (83 ) — — 30,791 (83 ) Total long-term marketable securities $ 122,816 $ (358 ) $ — $ — $ 122,816 $ (358 ) December 31, 2016 Less than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Marketable securities: U.S. government and agency securities $ 143,480 $ (56 ) $ 9,988 $ (12 ) $ 153,468 $ (68 ) Corporate debt securities 128,013 (180 ) — — 128,013 (180 ) Total marketable securities $ 271,493 $ (236 ) $ 9,988 $ (12 ) $ 281,481 $ (248 ) Long-term marketable securities: U.S. government and agency securities $ 129,163 $ (364 ) $ — $ — $ 129,163 $ (364 ) Corporate debt securities 53,643 (177 ) — — 53,643 (177 ) Total long-term marketable securities $ 182,806 $ (541 ) $ — $ — $ 182,806 $ (541 )

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis	The following tables set forth the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands): March 31, 2017 Level 1 Level 2 Level 3 Total Financial assets: Money market funds $ 169,007 $ — $ — $ 169,007 Commercial paper — 21,193 — 21,193 U.S. government and agency securities — 429,611 — 429,611 Corporate debt securities — 218,851 — 218,851 Equity securities 4,550 — — 4,550 Total financial assets $ 173,557 $ 669,655 $ — $ 843,212 Financial liabilities: Success payment liabilities $ — $ — $ 30,185 $ 30,185 Contingent consideration — — 21,348 21,348 Total financial liabilities $ — $ — $ 51,533 $ 51,533 December 31, 2016 Level 1 Level 2 Level 3 Total Financial assets: Money market funds $ 173,746 $ — $ — $ 173,746 Commercial paper — 64,260 — 64,260 U.S. government and agency securities — 457,181 — 457,181 Corporate debt securities — 222,289 — 222,289 Equity securities 1,700 — — 1,700 Total financial assets $ 175,446 $ 743,730 $ — $ 919,176 Financial liabilities: Success payment liabilities $ — $ — $ 22,786 $ 22,786 Contingent consideration — — 20,896 20,896 Total financial liabilities $ — $ — $ 43,682 $ 43,682
Summary of Changes in Fair Value of Level 3 Financial Liabilities	The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities (in thousands): Success Payment Liabilities Contingent Consideration Total Balance as of December 31, 2016 $ 22,786 $ 20,896 $ 43,682 Changes in fair value (1) 7,399 452 7,851 Balance as of March 31, 2017 $ 30,185 $ 21,348 $ 51,533 (1) The amount of success payment and contingent consideration milestones achieved, as well as the changes in fair value for success payment liabilities and contingent consideration, are recorded in research and development expense in the condensed consolidated statements of operations.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock-Based Compensation Expense	Stock-based compensation expense is recognized in the condensed consolidated statements of operations as follows (in thousands): Three Months Ended March 31, 2017 2016 Research and development (1) $ 10,329 $ 10,291 General and administrative 6,110 4,927 Total stock-based compensation expense (2) $ 16,439 $ 15,218 (1) Included in research and development stock-based compensation expense for the three months ended March 31, 2016 was $2.2 million related to the payout of employee stock options in connection with the AbVitro Inc. ("AbVitro") acquisition. (2) Included in stock-based compensation expense recognized for the three months ended March 31, 2017 and 2016 , is $1.0 million and $1.6 million , respectively, related to service providers other than employees, scientific founders, and directors, including $0.7 million and $1.2 million , respectively, for a former cofounding director who became a consultant upon his departure from the board of directors.
Total Stock-Based Compensation Cost Related to Unvested Awards Not Yet Recognized and Weighted Average Periods	Total stock-based compensation cost related to unvested awards not yet recognized and the weighted average periods over which the awards are expected to be recognized as of March 31, 2017 for all employees are as follows: Stock Options Restricted Stock Unrecognized stock-based compensation cost (in thousands) $ 142,691 $ 46,092 Expected weighted average period compensation costs to be recognized (years) 2.84 2.72
Summary of Restricted Stock and RSU Activity	A summary of the Company’s restricted stock and RSU activity is as follows (in thousands, except per share data): Restricted Stock Weighted Average Fair Value at Date of Grant per Share Unvested shares as of December 31, 2016 3,055 $ 7.10 Granted 1,226 20.82 Vested (636 ) 1.67 Forfeited (18 ) 18.53 Unvested shares as of March 31, 2017 3,627 $ 12.66
Summary of Stock Option Activity	A summary of the Company’s stock option activity is as follows (in thousands, except per share and contractual life data): Stock Options Weighted Weighted Average Remaining Contractual Life (years) Aggregate Intrinsic Value Outstanding as of December 31, 2016 8,521 $ 30.28 Granted 2,550 20.70 Exercised (31 ) 7.67 Forfeited/Cancelled (115 ) 36.89 Outstanding as of March 31, 2017 10,925 $ 28.02 8.75 $ 31,888 Exercisable as of March 31, 2017 2,852 $ 29.61 7.98 $ 14,654
Summary of Material Factors Incorporated in Black-Scholes Model in Estimating Fair Value of Options Granted to Employees and Consultants	The fair value of each stock option granted has been determined using the Black-Scholes option pricing model. The material factors incorporated in the Black-Scholes model in estimating the fair value of the options granted to employees, directors, and consultants included the following: Assumptions Three Months Ended March 31, 2017 Risk free interest rate 1.96% – 2.40% Expected volatility 75% Expected life (years) 6.02 - 9.40 Expected dividend yield 0%

Comprehensive Income (Loss) (Ta

Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Components of Accumulated Other Comprehensive Income (Loss) and Adjustments to Other Comprehensive Income (Loss)	The components of accumulated other comprehensive income (loss) and the adjustments to other comprehensive income (loss) are as follows (in thousands): Foreign Currency Translation Adjustments Net Unrealized Gain (Loss) on Marketable Securities Accumulated Other Comprehensive Income (Loss) Balance as of December 31, 2016 $ (1,791 ) $ (1,051 ) $ (2,842 ) Other comprehensive income 405 1,774 2,179 Balance as of March 31, 2017 $ (1,386 ) $ 723 $ (663 )

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2017
Earnings Per Share [Abstract]
Schedule of Diluted Net Loss Per Share Due to Anti-Dilutive Effect	The amounts in the table below were excluded from the calculation of diluted net loss per share for the periods indicated due to their anti-dilutive effect (in thousands): Three Months Ended March 31, 2017 2016 Unvested restricted stock and RSUs 3,627 4,983 Options to purchase common stock 10,925 7,471 Total 14,552 12,454

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Summary of Company's Future Minimum Lease Commitments	The following table summarizes the Company’s future minimum lease commitments as of March 31, 2017 (in thousands): Year ending December 31: 2017 $ 3,147 2018 11,498 2019 13,422 2020 13,568 2021 13,881 Thereafter 36,874 Total minimum lease payments $ 92,390

Significant Accounting Polici25

Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Organization And Basis Of Presentation [Line Items]
Accumulated deficit	$ (913,434)	$ (831,237)
Accounting Standards Update 2016-09
Organization And Basis Of Presentation [Line Items]
Deferred tax asset	7,100
Accounting Standards Update 2016-09 | Retained Earnings
Organization And Basis Of Presentation [Line Items]
Cumulative effect	$ 7,100

Collaboration and License Agr26

Collaboration and License Agreements - Celgene - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized during period		$ 19,327	$ 9,775
Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of outstanding common stock (in percentage)	9.76%
Share Purchase Agreement | Celgene | First Period Top-Up Rights
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of outstanding common stock to be acquired (in percentage)	10.00%
Share Purchase Agreement | Celgene | Top-Up Rights
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares sold (in shares)	75,568
Common stock, price per share (in usd per share)	$ 22.3882000318		$ 22.3882000318
Aggregate cash price of common stock sold	$ 1,700
Collaborative Arrangement | Celgene
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized during period		$ 19,100	$ 3,800

Collaboration and License Agr27

Collaboration and License Agreements - Fred Hutchinson Cancer Research Center - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Oct. 31, 2013	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expenses		$ 82,924	$ 73,722
Estimated fair value of total success payment obligation		45,800		$ 37,000
Success payment (expense) gain		7,400	(6,600)
Success payment liabilities		30,185		22,786
Collaborative Arrangement | Fred Hutchinson Cancer Research Center
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expenses		3,800	4,500
Estimated fair value of total success payment obligation		28,400		22,900
Success payment (expense) gain		4,400	$ (4,700)
Success payment liabilities		$ 17,700		$ 13,300
Collaboration agreement, term (in years)	6 years

Collaboration and License Agr28

Collaboration and License Agreements - Assumptions Used to Calculate Estimated Fair Value of Success Payment Liability (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of common stock (in usd per share)	$ 22.19
Memorial Sloan Kettering Cancer Center
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of common stock (in usd per share)	$ 22.19		$ 18.85
Expected volatility (in percentage)	75.00%	75.00%
Memorial Sloan Kettering Cancer Center | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk free interest rate (in percentage)	1.85%	1.90%
Expected term (in years)	4 years 7 months 21 days	4 years 10 months 22 days
Memorial Sloan Kettering Cancer Center | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk free interest rate (in percentage)	2.26%	2.31%
Expected term (in years)	7 years 7 months 21 days	7 years 10 months 22 days
Fred Hutchinson Cancer Research Center
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value of common stock (in usd per share)	$ 22.19		$ 18.85
Expected volatility (in percentage)	75.00%	75.00%
Fred Hutchinson Cancer Research Center | Minimum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk free interest rate (in percentage)	1.83%	1.88%
Expected term (in years)	4 years 6 months 16 days	4 years 9 months 16 days
Fred Hutchinson Cancer Research Center | Maximum
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk free interest rate (in percentage)	2.25%	2.30%
Expected term (in years)	7 years 6 months 19 days	7 years 9 months 16 days

Collaboration and License Agr29

Collaboration and License Agreements - Memorial Sloan Kettering Cancer Center - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Nov. 30, 2013	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expenses		$ 82,924	$ 73,722
Estimated fair value of total success payment obligation		45,800		$ 37,000
Success payment (expense) gain		7,400	(6,600)
Success payment liabilities		30,185		22,786
Collaborative Arrangement | Memorial Sloan Kettering Cancer Center
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement, term (in years)	5 years
Research and development expenses		1,600	700
Estimated fair value of total success payment obligation		17,400		14,100
Success payment (expense) gain		3,000	$ (1,900)
Success payment liabilities		$ 12,500		$ 9,500

Cash Equivalents and Marketab30

Cash Equivalents and Marketable Securities - Summary of Estimated Fair Value of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Cash equivalents:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 198,266	$ 184,792
Gross Unrealized Holding Gains	1	0
Gross Unrealized Holding Losses	(3)	(6)
Estimated Fair Value	198,264	184,786
Marketable securities:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	516,946	544,863
Gross Unrealized Holding Gains	6	69
Gross Unrealized Holding Losses	(476)	(248)
Estimated Fair Value	516,476	544,684
Marketable securities: | U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	326,269	320,224
Gross Unrealized Holding Gains	2	51
Gross Unrealized Holding Losses	(287)	(68)
Estimated Fair Value	325,984	320,207
Marketable securities: | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	21,193	64,260
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	21,193	64,260
Marketable securities: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	169,484	160,379
Gross Unrealized Holding Gains	4	18
Gross Unrealized Holding Losses	(189)	(180)
Estimated Fair Value	169,299	160,217
Long-term marketable securities:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	125,979	190,242
Gross Unrealized Holding Gains	2,851	5
Gross Unrealized Holding Losses	(358)	(541)
Estimated Fair Value	128,472	189,706
Long-term marketable securities: | U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	93,405	132,622
Gross Unrealized Holding Gains	1	4
Gross Unrealized Holding Losses	(275)	(364)
Estimated Fair Value	93,131	132,262
Long-term marketable securities: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	30,874	55,920
Gross Unrealized Holding Gains	0	1
Gross Unrealized Holding Losses	(83)	(177)
Estimated Fair Value	30,791	55,744
Long-term marketable securities: | Equity securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,700	1,700
Gross Unrealized Holding Gains	2,850	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	4,550	1,700
U.S. government and agency securities | Cash equivalents:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,495	4,712
Gross Unrealized Holding Gains	1	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	10,496	4,712
Money market funds | Cash equivalents:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	169,007	173,746
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	169,007	173,746
Corporate debt securities | Cash equivalents:
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,764	6,334
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	(3)	(6)
Estimated Fair Value	$ 18,761	$ 6,328

Cash Equivalents and Marketab31

Cash Equivalents and Marketable Securities - Summary of Gross Unrealized Holding Losses and Fair Value for Investments in Unrealized Loss Position (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Marketable securities:
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	$ 430,272	$ 271,493
Marketable securities, Unrealized Losses, Less than 12 Months	(461)	(236)
Marketable securities, Fair Value, 12 Months or Greater	9,985	9,988
Marketable securities, Unrealized Losses, 12 Months or Greater	(15)	(12)
Marketable securities, Fair Value, Total	440,257	281,481
Marketable securities, Unrealized Losses, Total	(476)	(248)
Marketable securities: | U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	289,772	143,480
Marketable securities, Unrealized Losses, Less than 12 Months	(272)	(56)
Marketable securities, Fair Value, 12 Months or Greater	9,985	9,988
Marketable securities, Unrealized Losses, 12 Months or Greater	(15)	(12)
Marketable securities, Fair Value, Total	299,757	153,468
Marketable securities, Unrealized Losses, Total	(287)	(68)
Marketable securities: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	140,500	128,013
Marketable securities, Unrealized Losses, Less than 12 Months	(189)	(180)
Marketable securities, Fair Value, 12 Months or Greater	0	0
Marketable securities, Unrealized Losses, 12 Months or Greater	0	0
Marketable securities, Fair Value, Total	140,500	128,013
Marketable securities, Unrealized Losses, Total	(189)	(180)
Long-term marketable securities:
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	122,816	182,806
Marketable securities, Unrealized Losses, Less than 12 Months	(358)	(541)
Marketable securities, Fair Value, 12 Months or Greater	0	0
Marketable securities, Unrealized Losses, 12 Months or Greater	0	0
Marketable securities, Fair Value, Total	122,816	182,806
Marketable securities, Unrealized Losses, Total	(358)	(541)
Long-term marketable securities: | U.S. government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	92,025	129,163
Marketable securities, Unrealized Losses, Less than 12 Months	(275)	(364)
Marketable securities, Fair Value, 12 Months or Greater	0	0
Marketable securities, Unrealized Losses, 12 Months or Greater	0	0
Marketable securities, Fair Value, Total	92,025	129,163
Marketable securities, Unrealized Losses, Total	(275)	(364)
Long-term marketable securities: | Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Marketable securities, Fair Value, Less than 12 Months	30,791	53,643
Marketable securities, Unrealized Losses, Less than 12 Months	(83)	(177)
Marketable securities, Fair Value, 12 Months or Greater	0	0
Marketable securities, Unrealized Losses, 12 Months or Greater	0	0
Marketable securities, Fair Value, Total	30,791	53,643
Marketable securities, Unrealized Losses, Total	$ (83)	$ (177)

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Financial Assets:
Total financial assets	$ 843,212	$ 919,176
Financial Liabilities:
Total financial liabilities	51,533	43,682
Money market funds
Financial Assets:
Total financial assets	169,007	173,746
Commercial paper
Financial Assets:
Total financial assets	21,193	64,260
U.S. government and agency securities
Financial Assets:
Total financial assets	429,611	457,181
Corporate debt securities
Financial Assets:
Total financial assets	218,851	222,289
Equity securities
Financial Assets:
Total financial assets	4,550	1,700
Success Payment Liabilities
Financial Liabilities:
Total financial liabilities	30,185	22,786
Contingent Consideration
Financial Liabilities:
Total financial liabilities	21,348	20,896
Level 1
Financial Assets:
Total financial assets	173,557	175,446
Financial Liabilities:
Total financial liabilities	0	0
Level 1 | Money market funds
Financial Assets:
Total financial assets	169,007	173,746
Level 1 | Commercial paper
Financial Assets:
Total financial assets	0	0
Level 1 | U.S. government and agency securities
Financial Assets:
Total financial assets	0	0
Level 1 | Corporate debt securities
Financial Assets:
Total financial assets	0	0
Level 1 | Equity securities
Financial Assets:
Total financial assets	4,550	1,700
Level 1 | Success Payment Liabilities
Financial Liabilities:
Total financial liabilities	0	0
Level 1 | Contingent Consideration
Financial Liabilities:
Total financial liabilities	0	0
Level 2
Financial Assets:
Total financial assets	669,655	743,730
Financial Liabilities:
Total financial liabilities	0	0
Level 2 | Money market funds
Financial Assets:
Total financial assets	0	0
Level 2 | Commercial paper
Financial Assets:
Total financial assets	21,193	64,260
Level 2 | U.S. government and agency securities
Financial Assets:
Total financial assets	429,611	457,181
Level 2 | Corporate debt securities
Financial Assets:
Total financial assets	218,851	222,289
Level 2 | Equity securities
Financial Assets:
Total financial assets	0	0
Level 2 | Success Payment Liabilities
Financial Liabilities:
Total financial liabilities	0	0
Level 2 | Contingent Consideration
Financial Liabilities:
Total financial liabilities	0	0
Level 3
Financial Assets:
Total financial assets	0	0
Financial Liabilities:
Total financial liabilities	51,533	43,682
Level 3 | Money market funds
Financial Assets:
Total financial assets	0	0
Level 3 | Commercial paper
Financial Assets:
Total financial assets	0	0
Level 3 | U.S. government and agency securities
Financial Assets:
Total financial assets	0	0
Level 3 | Corporate debt securities
Financial Assets:
Total financial assets	0	0
Level 3 | Equity securities
Financial Assets:
Total financial assets	0	0
Level 3 | Success Payment Liabilities
Financial Liabilities:
Total financial liabilities	30,185	22,786
Level 3 | Contingent Consideration
Financial Liabilities:
Total financial liabilities	$ 21,348	$ 20,896

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Financial Liabilities (Detail) - Level 3 $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 43,682
Changes in fair value	7,851
Ending balance	51,533
Success Payment Liabilities
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	22,786
Changes in fair value	7,399
Ending balance	30,185
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	20,896
Changes in fair value	452
Ending balance	$ 21,348

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of success payment obligations	$ 45,800		$ 37,000
Success payment (expense) gain	$ 7,400	$ (6,600)
Fair value of common stock (in usd per share)	$ 22.19
Success payment liabilities	$ (30,185)		$ (22,786)
Gain due to decrease in success payment liability	$ (6,300)
Estimated discount percentage rate of contingent consideration	16.00%
(Gain) expense recognized in change in fair value of the contingent consideration	$ 452	(1,012)
Stage Cell Therapeutics GmbH
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, less current portion	17,900
X-Body
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, less current portion	3,500
Stage And X-Body Inc | Research and Development Expense
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
(Gain) expense recognized in change in fair value of the contingent consideration	$ 400	$ (1,000)
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement of contingent consideration fair value, period in which milestones are expected to achieve	2,017
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Measurement of contingent consideration fair value, period in which milestones are expected to achieve	2,043
Stock Price Increased to 10%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs stock price sensitivity increase decrease (in usd per share)	10.00%
Share price sensitivity increase decrease (in usd per share)	$ 24.41
Success payment liabilities	$ (4,100)
Stock Price Decreased to 10%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs stock price sensitivity increase decrease (in usd per share)	(10.00%)
Share price sensitivity increase decrease (in usd per share)	$ 19.97
Success payment liabilities	$ (4,000)
Stock Price Increased to 35%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs stock price sensitivity increase decrease (in usd per share)	35.00%
Share price sensitivity increase decrease (in usd per share)	$ 29.96
Success payment liabilities	$ (14,500)
Stock Price Decreased to 35%
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value inputs stock price sensitivity increase decrease (in usd per share)	(35.00%)
Share price sensitivity increase decrease (in usd per share)	$ 14.42

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 16,439	$ 15,218
Research and developmen
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	10,329	10,291
General and Administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 6,110	$ 4,927

Stock-Based Compensation - Su36

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (non-printing) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense recognized	$ 16,439	$ 15,218
Service Providers
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense recognized	1,000	1,600
Former Co Founding Director
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense recognized	700	1,200
Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense recognized	$ 10,329	10,291
AbVitro Inc | Research and Development Expense
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense recognized		$ 2,200

Stock-Based Compensation - Tota

Stock-Based Compensation - Total Stock-Based Compensation Cost Related to Unvested Awards Not Yet Recognized and Weighted Average Periods (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 142,691
Expected weighted average period compensation costs to be recognized (usd per share)	2 years 10 months 1 day
Restricted Stock and RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation cost	$ 46,092
Expected weighted average period compensation costs to be recognized (usd per share)	2 years 8 months 21 days

Stock-Based Compensation - Su38

Stock-Based Compensation - Summary of Restricted Stock and RSU Activity (Detail) - Restricted Stock and RSUs shares in Thousands	3 Months Ended
	Mar. 31, 2017$ / sharesshares
Restricted Stock and RSUs
Unvested shares, Beginning balance | shares	3,055
Granted, Shares | shares	1,226
Vested, Shares | shares	(636)
Forfeited, Shares | shares	(18)
Unvested shares, Ending balance | shares	3,627
Weighted Average Fair Value at Date of Grant per Share
Beginning balance (usd per share) | $ / shares	$ 7.10
Granted (usd per share) | $ / shares	20.82
Vested (usd per share) | $ / shares	1.67
Forfeited (usd per share) | $ / shares	18.53
Ending balance (usd per share) | $ / shares	$ 12.66

Stock-Based Compensation - Su39

Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)$ / sharesshares
Stock Options
Beginning balance (shares) | shares	8,521
Granted (shares) | shares	2,550
Exercised (shares) | shares	(31)
Forfeited/Cancelled (shares) | shares	(115)
Ending balance (shares) | shares	10,925
Number of Stock Options, Exercisable (shares) | shares	2,852
Weighted Average Exercise Price per Share
Beginning balance (usd per share) | $ / shares	$ 30.28
Granted (usd per share) | $ / shares	20.70
Exercised (usd per share) | $ / shares	7.67
Forfeited/Cancelled (usd per share) | $ / shares	36.89
Ending balance (usd per share) | $ / shares	28.02
Weighted Average Exercise Price per Share, Exercisable (usd per share) | $ / shares	$ 29.61
Weighted Average Remaining Contractual Life (in years), Outstanding	8 years 9 months 1 day
Weighted Average Remaining Contractual Life (in years), Exercisable	7 years 11 months 24 days
Aggregate Intrinsic Value, Outstanding | $	$ 31,888
Aggregate Intrinsic Value, Exercisable | $	$ 14,654

Stock-Based Compensation - Su40

Stock-Based Compensation - Summary of Material Factors Incorporated in Black-Scholes Model in Estimating Fair Value of Options Granted to Employees and Consultants (Detail)	3 Months Ended
	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk free interest rate, minimum (percentage)	1.96%
Risk free interest rate, maximum (percentage)	2.40%
Expected volatility (percentage)	75.00%
Expected dividend yield (percentage)	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	6 years 8 days
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	9 years 4 months 26 days

Comprehensive Income (Loss) - C

Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Income (Loss) and Adjustments to Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Opening balance	$ 1,077,701
Other comprehensive income (loss)	2,179	$ 1,183
Ending balance	1,016,052
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Opening balance	(2,842)
Other comprehensive income (loss)	2,179
Ending balance	(663)
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Opening balance	(1,791)
Ending balance	(1,386)
Net Unrealized Gain (Loss) on Marketable Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Opening balance	(1,051)
Ending balance	$ 723

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Tax Disclosure [Line Items]
Income tax benefit	$ (1,332)	$ (7,353)
Pre-tax loss	$ 83,529	78,491
AbVitro Inc
Income Tax Disclosure [Line Items]
Deferred income tax expense benefit connection with acquisition		(6,700)
Juno GmbH
Income Tax Disclosure [Line Items]
Income tax benefit		$ 700

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Diluted Net Loss Per Share Due to Anti-Dilutive Effect (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	14,552	12,454
Unvested restricted stock and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	3,627	4,983
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the calculation of diluted net loss per share (in shares)	10,925	7,471

Commitments and Contingencies -

Commitments and Contingencies - Summary of Company's Future Minimum Lease Commitments (Detail) $ in Thousands	Mar. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,017	$ 3,147
2,018	11,498
2,019	13,422
2,020	13,568
2,021	13,881
Thereafter	36,874
Total minimum lease payments	$ 92,390

Commitments and Contingencies45

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 2.6	$ 1.1

Related-Party Transactions - Ad

Related-Party Transactions - Additional Information (Detail)	Mar. 31, 2017
Celgene
Related Party Transaction [Line Items]
Common stock holding percentage, more than (in percentage)	5.00%