bluebird bio (BLUE) 10-Q 7 Aug 15 2015 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2015	Jul. 31, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q2
Trading Symbol	BLUE
Entity Registrant Name	bluebird bio, Inc.
Entity Central Index Key	1,293,971
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		36,263,621

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 593,299	$ 347,845
Marketable securities	217,208	125,710
Deferred tax assets	399	1,913
Prepaid expenses and other current assets	4,546	4,521
Total current assets	815,452	479,989
Marketable securities	125,938	18,448
Property and equipment, net	16,803	15,740
Intangible assets, net	26,337	28,219
Goodwill	13,128	13,128
Restricted cash and other non-current assets	1,511	1,215
Total assets	999,169	556,739
Current liabilities:
Accounts payable	2,339	2,954
Accrued expenses and other current liabilities	20,024	14,649
Deferred revenue, current portion	5,670	25,375
Total current liabilities	28,033	42,978
Deferred rent, net of current portion	8,223	8,674
Deferred revenue, net of current portion	38,724	5,302
Contingent consideration, net of current portion	4,590	6,321
Deferred tax liabilities	399	1,913
Other non-current liabilities	234	294
Total liabilities	$ 80,203	$ 65,482
Commitments and contingencies (Note 6)
Stockholders' equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at June 30, 2015 and December 31, 2014
Common stock, $0.01 par value, 125,000 shares authorized; 35,958 and 32,340 shares issued and outstanding at June 30, 2015 and December 31, 2014, respectively	$ 360	$ 323
Additional paid-in capital	1,142,625	638,389
Accumulated other comprehensive loss	(53)	(71)
Accumulated deficit	(223,966)	(147,384)
Total stockholders' equity	918,966	491,257
Total liabilities and stockholders' equity	$ 999,169	$ 556,739

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	35,958,000	32,340,000
Common stock, shares outstanding	35,958,000	32,340,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenue:
Collaboration revenue	$ 4,940	$ 6,250	$ 11,284	$ 12,500
Research and license fees		85		170
Total revenue	4,940	6,335	11,284	12,670
Operating expenses:
Research and development	44,266	13,931	67,985	25,394
General and administrative	10,724	5,738	18,060	11,277
Change in fair value of contingent consideration	1,973		2,188
Total operating expenses	56,963	19,669	88,233	36,671
Loss from operations	(52,023)	(13,334)	(76,949)	(24,001)
Other income, net	228	11	367	69
Loss before income taxes	(51,795)	(13,323)	(76,582)	(23,932)
Benefit from income taxes		11,797		11,797
Net loss	(51,795)	(1,526)	(76,582)	(12,135)
Other comprehensive loss:
Unrealized gain on available-for-sale securities, net of tax	70		18
Comprehensive loss	$ (51,725)	$ (1,526)	$ (76,564)	$ (12,135)
Net loss per share - basic and diluted:	$ (1.57)	$ (0.06)	$ (2.34)	$ (0.50)
Weighted-average number of common shares used in computing net loss per share - basic and diluted:	32,955	24,474	32,757	24,312

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Operating activities
Net loss	$ (76,582)	$ (12,135)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash benefit on release of tax valuation allowance		(11,797)
Depreciation and amortization	3,509	1,017
Stock-based compensation expense	21,482	4,843
Change in fair value of contingent consideration	2,188
Other non-cash items	269	168
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,059)	854
Accounts payable	(418)	(2,702)
Accrued expenses and other liabilities	1,098	7,674
Deferred revenue	13,716	(12,670)
Deferred rent	(480)	1,490
Net cash used in operating activities	(36,277)	(23,258)
Investing activities
Restricted cash	359
Purchase of property and equipment	(2,568)	(4,534)
Acquisition of business, net of cash acquired		(4,673)
Purchases of marketable securities	(261,440)
Proceeds from maturities of marketable securities	62,680
Net cash used in investing activities	(200,969)	(9,207)
Financing activities
Proceeds from public offering of common stock, net of issuance costs	477,179
Proceeds from issuance of common stock	5,521	1,896
Net cash provided by financing activities	482,700	1,896
Increase (decrease) in cash and cash equivalents	245,454	(30,569)
Cash and cash equivalents at beginning of period	347,845	206,279
Cash and cash equivalents at end of period	593,299	175,710
Non-cash investing and financing activities:
Assets acquired in acquisition		43,759
Liabilities assumed in acquisition		12,768
Equity issued in acquisition		19,348
Purchases of property and equipment included in accounts payable and accrued expenses	524	344
Offering expenses included in accounts payable and accrued expenses	115	45
Stock option exercise proceeds receivable	$ 181	$ 75

Description of the business

Description of the business	6 Months Ended
	Jun. 30, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of the business	1. Description of the business bluebird bio, Inc. (the “Company” or “bluebird”) was incorporated in Delaware on April 16, 1992, and is headquartered in Cambridge, Massachusetts. The Company was formed to develop, manufacture and market therapies to safely and effectively deliver genes useful in the treatment of severe genetic and rare diseases and in the field of T cell-based immunotherapy. Since its inception, the Company has devoted substantially all of its resources to its research and development efforts relating to its product candidates, including activities to manufacture product candidates, conduct clinical studies of its product candidates, perform preclinical research to identify new product candidates and provide general and administrative support for these operations. In June 2015, the Company sold 2,941,176 shares of common stock through an underwritten public offering at a price of $170.00 per share. The aggregate net proceeds received by the Company from the offering were $477.2 million, net of underwriting discounts and commissions and estimated offering expenses payable by the Company of approximately $22.8 million.

Summary of significant accounti

Summary of significant accounting policies and basis of presentation	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Summary of significant accounting policies and basis of presentation	2. Summary of significant accounting policies and basis of presentation Basis of presentation and principles of consolidation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States (“GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended June 30, 2015 and 2014. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on February 25, 2015. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries: Precision Genome Engineering, Inc. (“Pregenen”), bluebird bio France – SARL, bluebird bio Australia Pty Ltd. and bluebird bio Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to GAAP. The Company views its operations and manages its business in one operating segment. All material long-lived assets of the Company reside in the United States. Summary of accounting policies The significant accounting policies and estimates used in preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the six months ended June 30, 2015. Contingent consideration Each reporting period, the Company revalues the contingent consideration obligations associated with business combinations to their fair value and records within operating expenses increases in their fair value as contingent consideration expense and decreases in the fair value as contingent consideration income. Changes in contingent consideration result from changes in the assumptions regarding probabilities of successful achievement of related milestones, the estimated timing in which the milestones are achieved and the discount rate used to estimate the fair value of the liability. Contingent consideration may change significantly as development of the Company’s programs in certain indications progress and additional data are obtained, impacting the Company’s assumptions. The assumptions used in estimating fair value require significant judgment. The use of different assumptions and judgments could result in a materially different estimate of fair value. See Note 4, “Fair value measurements,” for additional information. Net income (loss) per share Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options, unvested restricted stock, restricted stock units, employee stock purchase plan, warrants, and acquisition holdback shares using the treasury stock method. Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Estimates are used in the following areas, among others: fair value estimates used to assess potential impairment of long-lived assets, contingent consideration, stock-based compensation expense, accrued expenses, revenue and income taxes. Actual results could materially differ from those estimates.

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2015
Investments Debt And Equity Securities [Abstract]
Marketable securities	3. Marketable securities The following table summarizes the available-for-sale securities held at June 30, 2015 and December 31, 2014 (in thousands): Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value June 30, 2015 U.S. government agency securities $ 329,359 $ 29 $ (89 ) $ 329,299 Certificates of deposit 13,840 8 (1 ) 13,847 Total $ 343,199 $ 37 $ (90 ) $ 343,146 December 31, 2014 U.S. government agency securities $ 131,589 $ 6 $ (59 ) $ 131,536 Certificates of deposit 12,640 — (18 ) 12,622 Total $ 144,229 $ 6 $ (77 ) $ 144,158 No available-for-sale securities held as of June 30, 2015 or December 31, 2014 had remaining maturities greater than two years.

Fair value measurements

Fair value measurements	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Fair value measurements	4. Fair value measurements The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of June 30, 2015 and December 31, 2014 (in thousands): Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) June 30, 2015 Assets: Cash and cash equivalents $ 593,299 $ 593,299 $ — $ — Marketable securities: U.S. government agency securities 329,299 — 329,299 — Certificates of deposit 13,847 — 13,847 — Total assets $ 936,445 $ 593,299 $ 343,146 $ — Liabilities: Contingent consideration $ 7,984 $ — $ — $ 7,984 Total liabilities $ 7,984 $ — $ — $ 7,984 December 31, 2014 Assets: Cash and cash equivalents $ 347,845 $ 347,845 $ — $ — Marketable securities: U.S. government agency securities 131,536 — 131,536 — Certificates of deposit 12,622 — 12,622 — Total assets $ 492,003 $ 347,845 $ 144,158 $ — Liabilities: Contingent consideration $ 6,796 $ — $ — $ 6,796 Total liabilities $ 6,796 $ — $ — $ 6,796 Cash and cash equivalents The Company considers all highly liquid securities with original final maturities of three months or less from the date of purchase to be cash equivalents. As of June 30, 2015 and December 31, 2014, cash and cash equivalents comprise funds in cash and money market accounts. Marketable securities The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At June 30, 2015 and December 31, 2014, the balance in the Company’s accumulated other comprehensive loss was composed solely of activity related to the Company’s available-for-sale marketable securities. There were no realized gains or losses recognized on the sale or maturity of available-for-sale securities during the six months ended June 30, 2015, and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive income for the same period. The aggregate fair value of securities held by the Company in an unrealized loss position for less than twelve months as of June 30, 2015 and December 31, 2014 was $181.3 million and $134.4 million, respectively. The Company has the intent and ability to hold such securities until recovery. The Company determined that there was no material change in the credit risk of the above investments. As a result, the Company determined it did not hold any investments with an other-than-temporary impairment as of June 30, 2015 and December 31, 2014. Contingent consideration In connection with the acquisition of Pregenen, the Company recorded contingent consideration pertaining to the amounts potentially payable to Pregenen’s former equityholders pursuant to the Stock Purchase Agreement (the “Stock Purchase Agreement”) by and among the Company, Pregenen and Pregenen’s former equityholders. 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. Future changes in the fair value of contingent consideration related to updated assumptions and estimates are recognized within the condensed consolidated statements of operations and comprehensive loss. 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, considerable judgment is required to interpret the market 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 preclinical, clinical and commercial milestones, the period in which these milestones are expected to be achieved ranging from 2016 to 2026 and discount rates ranging from 10.5% to 14.7%. Significant increases or decreases in any of the probabilities of success would result in a significantly higher or lower fair value measurement, respectively. Significant increases or decreases in these other inputs would result in a significantly lower or higher fair value measurement, respectively. The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations, which include Level 3 inputs (in thousands): Six Months Ended June 30, 2015 Beginning balance $ 6,796 Additions — Changes in fair value 2,188 Reclassification to accrued expenses (1,000 ) Payments — Ending balance $ 7,984 As of June 30, 2015, $3.4 million of the fair value of the Company’s total contingent consideration obligations was reflected as a component of accrued expenses and other current liabilities within the condensed consolidated balance sheets, with the remaining balance of $4.5 million reflected as a non-current liability. During the second quarter of 2015, a $1.0 million milestone under the Stock Purchase Agreement was achieved and was recorded in accrued expenses and other current liabilities as of June 30, 2015. $1.0 million was paid to the former equityholders of Pregenen during the third quarter of 2015.

Accrued expenses and other curr

Accrued expenses and other current liabilities	6 Months Ended
	Jun. 30, 2015
Payables And Accruals [Abstract]
Accrued expenses and other current liabilities	5. Accrued expenses and other current liabilities Accrued expenses and other current liabilities consist of the following (in thousands): June 30, 2015 December 31, 2014 Employee compensation $ 3,937 $ 4,943 Accrued good and services 10,303 7,358 Accrued professional fees 1,090 428 Deferred rent, current portion 885 914 Contingent consideration, current portion 3,394 475 Other 415 531 Total accrued expenses and other current liabilities $ 20,024 $ 14,649 The change in fair value of contingent consideration was primarily related to an increase in the probability of successful achievement of milestones expected to be achieved within the next twelve months.

Commitments and contingencies

Commitments and contingencies	6 Months Ended
	Jun. 30, 2015
Commitments And Contingencies Disclosure [Abstract]
Commitments and contingencies	6. Commitments and contingencies The Company is party to various agreements, principally relating to licensed technology, that require future payments relating to milestones not met at June 30, 2015 and December 31, 2014 or royalties on future sales of specified products. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to these agreements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified party for losses suffered or incurred by the indemnified party, generally the Company’s business partners or customers, in connection with claims by any third party with respect to the Company’s products or business activities. The term of these indemnification agreements is generally perpetual any time after execution of the agreement. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited. The Company has never incurred costs to defend lawsuits or settle claims related to these indemnification agreements. The Company’s wholly-owned subsidiary bluebird bio France – SARL participates in the French Crédit d’Impôt Recherche (“CIR”) program, which allows companies to monetize up to 30% of eligible research expenses. The Company received aggregate reimbursement of €1.1 million related to years 2011 through 2013. The Company applied for €0.7 million related to 2014, which was classified in current assets within the condensed consolidated balance sheets as of June 30, 2015 and was received during the third quarter of 2015. The Company has not yet applied for €0.3 million related to the six months ended June 30, 2015, which is classified as non-current assets within the condensed consolidated balance sheets as of June 30, 2015. The years 2011 through 2015 are open and subject to examination. On June 30, 2014, the Company acquired Pregenen. During the second quarter of 2015, a $1.0 million milestone under the Stock Purchase Agreement was achieved, which resulted in a $1.0 million payment to the former equityholders of Pregenen during the third quarter of 2015. The Company may be required to make up to an additional $134.0 million in future contingent cash payments to the former equityholders of Pregenen upon the achievement of certain preclinical, clinical and commercial milestones related to the Pregenen technology, of which $14.0 million relates to preclinical milestones, $20.1 million relates to clinical milestones and $99.9 million relates to commercial milestones. In accordance with accounting for business combinations guidance, contingent consideration liabilities are required to be recognized on the condensed consolidated balance sheets at fair value. Estimating the fair value of contingent consideration requires the use of significant assumptions primarily relating to probabilities of successful achievement of certain preclinical, clinical and commercial milestones, the expected timing in which these milestones will be achieved and discount rates. The use of different assumptions could result in materially different estimates of fair value. See Note 4, “Fair value measurements,” for additional information. On June 29, 2015, the Company entered into a lease agreement for additional office space located at 215 First Street, Cambridge, Massachusetts. Under the terms of the lease, the Company leased approximately 15,120 square feet starting on July 13, 2015 for $483,840 per year in base rent, which is subject to a 3% annual increase plus certain operating expenses and taxes. The lease will continue until the end of the sixtieth full calendar month following the date the landlord delivers the premises to the Company. Under the terms of the lease, the Company will also lease an additional 8,075 square feet of office space in the same premises starting on January 1, 2016 for an additional $258,400 per year in base rent, which is subject to a 3% annual increase plus certain operating expenses and taxes.

Significant agreements

Significant agreements	6 Months Ended
	Jun. 30, 2015
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Significant agreements	7. Significant agreements Celgene Corporation Original Collaboration Agreement On March 19, 2013, the Company entered into a Master Collaboration Agreement (the “Collaboration Agreement”) with Celgene Corporation (“Celgene”) to discover, develop and commercialize potentially disease-altering gene therapies in oncology. The collaboration is focused on applying gene therapy technology to genetically modify a patient’s own T cells, known as chimeric antigen receptor, or CAR T cells, to target and destroy cancer cells. Additionally, on March 19, 2013, the Company entered into a Platform Technology Sublicense Agreement (the “Sublicense Agreement”) with Celgene pursuant to which the Company obtained a sublicense to certain intellectual property from Celgene, originating under Celgene’s license from Baylor College of Medicine, for use in the collaboration. Under the terms of the Collaboration Agreement, the Company received a $75.0 million up-front, non-refundable cash payment. The Company is responsible for conducting discovery, research and development activities through completion of Phase I clinical studies, if any, during the initial term of the agreement, or three years. The collaboration is governed by a joint steering committee (“JSC”) formed by an equal number of representatives from the Company and Celgene. The JSC, among other activities, review the collaboration program, review and evaluate product candidates and approve regulatory plans. In addition to the JSC, the Collaboration Agreement provides that the Company and Celgene each appoint representatives to a patent committee, which is responsible for managing the intellectual property developed and used during the collaboration. Summary of the Amended Collaboration Agreement On June 3, 2015, the Company and Celgene amended and restated the Collaboration Agreement (the “Amended Collaboration Agreement”). Under the Amended Collaboration Agreement, the parties will now focus the collaboration exclusively on anti- B-cell maturation antigen (“BCMA”) product candidates for an additional three-year term. In connection with the Amended Collaboration Agreement, the Company received an upfront, one-time, non-refundable, non-creditable payment of $25.0 million to fund research and development under the collaboration. The collaboration will continue to be governed by the JSC. Under the terms of the Amended Collaboration Agreement, for up to two product candidates selected for development under the collaboration, the Company is responsible for conducting and funding all research and development activities performed up through completion of the initial Phase I clinical study, if any, of such product candidate. On a product candidate-by-product candidate basis, up through a specified period following enrollment of the first patient in an initial Phase I clinical study for such product candidate (the “Option Period”), the Company has granted Celgene an option to obtain an exclusive worldwide license to develop and commercialize such product candidate pursuant to a written agreement, the form of which the Company has already agreed upon, provided that, if Celgene does not exercise its option with respect to the first product candidate under the Amended Collaboration Agreement prior to the expiration of the applicable Option Period then it will not be permitted to exercise its option with respect to any future product candidates under the Amended Collaboration Agreement. In the event that Celgene exercises its option with respect to any product candidate, the Company may elect to co-develop and co-promote the product candidate in the United States, provided that, if the Company does not exercise its option co-develop and co-promote the first product candidate in-licensed by Celgene under the Amended Collaboration Agreement, then the Company will not be permitted to exercise its option to co-develop and co-promote any future product candidates under the Amended Collaboration Agreement. If Celgene elects to exercise its option to exclusively in-license a product candidate, it must pay the Company an option fee in the amount of $10.0 million for the first product candidate and $15.0 million for any additional product candidates, plus an additional fee in the amount of $10.0 million in the event the Company does not exercise its option to co-develop and co-promote that product candidate in the United States. In addition to the applicable option fee, for each product candidate that is in-licensed by Celgene, and for which the Company does not exercise its option to the Company will be eligible to receive up to $10.0 million in clinical milestone payments, up to $117.0 million in regulatory milestone payments and up to $78.0 million in commercial milestone payments. The Company will also be eligible to receive If the Company elects to co-develop and co-promote a product candidate licensed by Celgene, then the Company and Celgene would share equally in all costs incurred relating to the development, commercialization and manufacturing of the product candidate within the United States and share equally in the profits generated by such product candidate in the United States. Additionally, if the Company elects to co-develop and co-promote a product candidate, then the milestones and royalties would decrease compared to those described above. Under this scenario, the Company would receive, per product, up to $10.0 million in clinical milestone payments and, outside of the United States, up to $54.0 million in regulatory milestone payments and up to $36.0 million in commercial milestone payments. In addition, to the extent any of the product candidates licensed by Celgene and co-developed and co-promoted by the Company are commercialized, the Company would be entitled to receive tiered royalty payments ranging from the mid-single digits to low-teens based on a percentage of net sales from sales generated outside of the United States. The royalties payable to the Company are subject to certain reductions, including for any royalty payments required to be made by Celgene to acquire patent rights, with an aggregate minimum floor. The co-development and co-promotion agreement would be governed by a joint governance committee, or JGC, formed by representatives from the Company and Celgene. The JGC will, among other activities, supervise the overall performance of the development and commercialization of elected product candidates and licensed products for United States administration. Celgene is solely responsible for the manufacture and supply of drug product for any optioned product candidate. Under the Amended Collaboration Agreement, subject to customary “back-up” supply rights granted to Celgene, the Company has the sole right to manufacture or have manufactured supplies of vectors and associated payloads manufactured for incorporation into the optioned product candidate. Celgene would reimburse the Company for its costs to manufacture and supply such vectors and associated payloads, plus a mid-single digit mark-up. If Celgene does not exercise its option with respect to any product candidate prior to expiration of the applicable option period, then the Company has the right to develop that product candidate outside the scope of the Amended Collaboration Agreement. Either party may terminate the Amended Collaboration Agreement upon written notice to the other party in the event of the other party’s uncured material breach. Celgene may terminate the Amended Collaboration Agreement for any reason upon prior written notice to the Company. If the agreement is terminated, rights to product candidates in development at the time of such termination will be allocated to the parties through a mechanism included in the agreement. In addition, if Celgene terminates the agreement for the Company’s breach, any then-existing co-development and co-promotion agreement will be automatically terminated and replaced with a license agreement for such product candidate and any amounts payable by Celgene under any then-existing product license agreements will be reduced. Under the Amended Collaboration Agreement, the so-called “call option” under the prior collaboration agreement, pursuant to which Celgene had the option to terminate the collaboration agreement and obtain fully paid-up licenses to product candidates in the event of a change of control transaction involving the Company, has been eliminated. Under the Sublicense Agreement, the Company will continue to have access to certain intellectual property rights in-licensed to Celgene pursuant to its collaboration agreement with the Baylor College of Medicine, which was first established in connection with the initiation of the original Collaboration Agreement between the Company and Celgene. Accounting Analysis The Company’s Amended Collaboration Agreement with Celgene contains the following deliverables: (i) research and development services, (ii) participation on the JSC, (iii) participation on the patent committee, (iv) a license to the first product candidate, (v) manufacture of vectors and associated payload for incorporation into the first optioned product candidate under the license, and (vi) participation on the JGC under the co-development and co-promotion agreement for the first optioned product candidate under the license. The license to the first product candidate is considered a deliverable at the inception of the arrangement and therefore the associated option fee is included in allocable arrangement consideration. The Company believes there is minimal risk with regard to whether Celgene will exercise the option based on the successful completion of preclinical activities and proximity of enrollment of the first patient in an initial Phase I clinical study for this product candidate. Further, Celgene loses the right to option any other product candidates if it does not agree to license the first product candidate. The Company has determined that the obligation within the license to manufacture or have manufactured supplies of vectors and associated payloads for incorporation into the first optioned product candidate is a deliverable, consistent with the option to license the first product candidate. However, the Company has determined that the options to license any additional product candidates are substantive options and therefore are not considered deliverables at execution of the Amended Collaboration Agreement. Celgene is not contractually obligated to exercise the options. Additionally, as a result of the uncertain outcome of the discovery, research and development activities, the Company is at risk with regard to whether Celgene will exercise the options to license additional product candidates. Moreover, the Company has determined that the options are not priced at a significant and incremental discount. Accordingly, the options to other product candidates are not considered deliverables at the inception of the arrangement and the associated option fees are not included in allocable arrangement consideration. The Company concluded that each of the three delivered elements at the inception of the agreement (research and development services, participation on the JSC and participation on the patent committee) has standalone value from the other undelivered elements. Additionally, the Amended Collaboration Agreement does not include return rights related to the collaboration term. Accordingly, each deliverable qualifies as a separate unit of accounting. The Company determined that each of the identified deliverables have the same period of performance (the three year term through projected initial Phase I study completion) and have the same pattern of revenue recognition, ratably over the period of performance as there is no other discernible pattern of recognition. The Company identified the allocable arrangement consideration as the $25.0 million up-front research and development funding payment, $10.0 million option fee for the first product candidate, $20.0 million related to remaining deferred revenue from the original Collaboration Agreement, and $54.1 million of contingent revenue related to the estimated amounts that will be received from Celgene for manufacturing services. The $109.0 million total allocable arrangement consideration was allocated based on the relative estimated selling price of the separate units of accounting at the inception of the amended agreement, resulting in $17.3 million allocated to the three delivered elements at the inception of the agreement, which will be recognized over an initial three year term. This initial term will be revisited as the development plan timing changes or other events that impact the period over which the Company’s obligations relate. The Company evaluated all of the milestones that may be received in connection with Celgene’s option to license a product candidate resulting from the collaboration. In evaluating if a milestone is substantive, the Company assesses whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All clinical and regulatory milestones that may be received under the option to the license agreement are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. During each of the six months ended June 30, 2015 and 2014, the Company recognized $11.3 million and $12.5 million, respectively, of revenue associated with its collaboration with Celgene related to the recognition of discovery, research and development services. As of June 30, 2015 and December 31, 2014, there was $44.4 million and $30.7 million, respectively, of total deferred revenue related to the Company’s collaboration with Celgene, which is classified as current or non-current in the condensed consolidated balance sheets, $16.9 million of which will be recognized over three years with the remaining amount deferred until a later date.

Stock-based compensation and wa

Stock-based compensation and warrants	6 Months Ended
	Jun. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based compensation and warrants	8. Stock-based compensation and warrants In January 2015, the number of shares of common stock available for issuance under the 2013 Stock Option and Incentive Plan (“2013 Plan”) was increased by approximately 1.3 million shares as a result of the automatic increase provision of the 2013 Plan. As of June 30, 2015, the total number of shares of common stock available for issuance under the 2013 Plan was approximately 0.9 million. Stock-based compensation expense Stock-based compensation expense by award type was as follows (in thousands): Three months ended June 30, Six months ended June 30, 2015 2014 2015 2014 Stock options $ 15,310 $ 2,335 $ 20,065 $ 4,812 Restricted stock awards — 16 — 31 Restricted stock units 668 — 1,285 — Employee stock purchase plan 72 — 132 — $ 16,050 $ 2,351 $ 21,482 $ 4,843 As of June 30, 2015, the Company had $80.5 million of unrecognized stock-based compensation expense, net of estimated forfeitures, related to unvested stock options, restricted stock units, and the employee stock purchase plan that is expected to be recognized over a weighted-average period of 2.9 years. On January 29, 2015, the Company entered into a Transitional Services and Separation Agreement with its Chief Scientific Officer, ending his employment with the Company effective July 6, 2015. Subsequent to this separation date, he is serving as a member of the Company’s Scientific Advisory Board. Under the terms of the agreement, outstanding options held by the Chief Scientific Officer were modified. The incremental value of the modification was estimated to be $3.0 million using a Black-Scholes option valuation model, which is being recognized within research and development expense on a straight-line basis through the date of separation. As a result of the modification, the Company recognized $1.8 million and $2.8 million of stock-based compensation expense during the three and six months ended June 30, 2015, respectively. On April 10, 2015, the Company modified the vesting conditions of a stock option award held by a non-employee founder, which resulted in $6.7 million of stock-based compensation expense recognized to research and development expense during the second quarter of 2015. Restricted stock units The following table summarizes the restricted stock unit activity under the Company’s equity award plans (shares in thousands): Shares Weighted-average grant date fair value Unvested balance at December 31, 2014 179 $ 30.47 Granted 25 $ 179.30 Vested — — Forfeited (1 ) $ 30.47 Unvested balance at June 30, 2015 203 $ 48.77 Stock options The following table summarizes the stock option activity under the Company’s equity award plans (shares in thousands): Shares Weighted-average exercise price per share Outstanding at December 31, 2014 3,652 $ 12.30 Granted 915 $ 106.87 Exercised (671 ) $ 7.97 Canceled or forfeited (43 ) $ 44.68 Outstanding at June 30, 2015 3,853 $ 35.15 Exercisable at June 30, 2015 1,325 $ 7.89 Vested and expected to vest at June 30, 2015 3,776 $ 35.61 Options exercisable for approximately 0.7 million shares of common stock were exercised during the six months ended June 30, 2015, resulting in total proceeds to the Company of $5.3 million. In accordance with the Company’s stock option plans, the shares were issued from a pool of shares reserved for issuance under the stock option plans. Employee stock purchase plan The Company’s 2013 Employee Stock Purchase Plan (“2013 ESPP”) authorizes the initial issuance of up to a total of 238,000 shares of the Company’s common stock to participating employees. The first offering period under the 2013 ESPP closed on January 31, 2015, resulting in the purchase of 6,780 common shares. Warrants As of June 30, 2015 and December 31, 2014, the Company had 0.2 million warrants outstanding to purchase common stock. During the six months ended June 30, 2015, there were no warrants exercised and no cancellations or expirations.

Income taxes

Income taxes	6 Months Ended
	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income taxes	9. Income taxes Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. The Company has allocated its valuation allowance in accordance with the provisions of ASC 740, Income Taxes

Net loss per share

Net loss per share	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Net loss per share	10. Net loss per share The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands): Three and six months ended June 30, 2015 2014 Warrants 177 338 Outstanding stock options 3,853 4,112 Unvested restricted stock — 27 Restricted stock units 203 — ESPP shares 4 — Acquisition holdback 94 94 4,331 4,571

Summary of significant accoun16

Summary of significant accounting policies and basis of presentation (Policies)	6 Months Ended
	Jun. 30, 2015
Accounting Policies [Abstract]
Basis of presentation and principles of consolidation	Basis of presentation and principles of consolidation The accompanying condensed consolidated financial statements are unaudited and have been prepared by the Company in accordance with accounting principles generally accepted in the United States (“GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). Certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. These interim condensed consolidated financial statements, in the opinion of management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended June 30, 2015 and 2014. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on February 25, 2015. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries: Precision Genome Engineering, Inc. (“Pregenen”), bluebird bio France – SARL, bluebird bio Australia Pty Ltd. and bluebird bio Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. Any reference in these notes to applicable guidance is meant to refer to GAAP. The Company views its operations and manages its business in one operating segment. All material long-lived assets of the Company reside in the United States.
Summary of accounting policies	Summary of accounting policies The significant accounting policies and estimates used in preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the six months ended June 30, 2015.
Contingent consideration	Contingent consideration Each reporting period, the Company revalues the contingent consideration obligations associated with business combinations to their fair value and records within operating expenses increases in their fair value as contingent consideration expense and decreases in the fair value as contingent consideration income. Changes in contingent consideration result from changes in the assumptions regarding probabilities of successful achievement of related milestones, the estimated timing in which the milestones are achieved and the discount rate used to estimate the fair value of the liability. Contingent consideration may change significantly as development of the Company’s programs in certain indications progress and additional data are obtained, impacting the Company’s assumptions. The assumptions used in estimating fair value require significant judgment. The use of different assumptions and judgments could result in a materially different estimate of fair value. See Note 4, “Fair value measurements,” for additional information.
Net income (loss) per share	Net income (loss) per share Basic net income (loss) per share is calculated by dividing net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding during the period. Diluted net income per share is calculated by dividing the net income attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from outstanding stock options, unvested restricted stock, restricted stock units, employee stock purchase plan, warrants, and acquisition holdback shares using the treasury stock method.
Use of estimates	Use of estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts in the financial statements and accompanying notes. Estimates are used in the following areas, among others: fair value estimates used to assess potential impairment of long-lived assets, contingent consideration, stock-based compensation expense, accrued expenses, revenue and income taxes. Actual results could materially differ from those estimates.

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2015
Investments Debt And Equity Securities [Abstract]
Summary of Available for Sale Securities Held	The following table summarizes the available-for-sale securities held at June 30, 2015 and December 31, 2014 (in thousands): Description Amortized Cost Unrealized Gains Unrealized Losses Fair Value June 30, 2015 U.S. government agency securities $ 329,359 $ 29 $ (89 ) $ 329,299 Certificates of deposit 13,840 8 (1 ) 13,847 Total $ 343,199 $ 37 $ (90 ) $ 343,146 December 31, 2014 U.S. government agency securities $ 131,589 $ 6 $ (59 ) $ 131,536 Certificates of deposit 12,640 — (18 ) 12,622 Total $ 144,229 $ 6 $ (77 ) $ 144,158

Fair value measurements (Tables

Fair value measurements (Tables)	6 Months Ended
	Jun. 30, 2015
Fair Value Disclosures [Abstract]
Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following table sets forth the Company’s assets and liabilities that are measured at fair value on a recurring basis as of June 30, 2015 and December 31, 2014 (in thousands): Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) June 30, 2015 Assets: Cash and cash equivalents $ 593,299 $ 593,299 $ — $ — Marketable securities: U.S. government agency securities 329,299 — 329,299 — Certificates of deposit 13,847 — 13,847 — Total assets $ 936,445 $ 593,299 $ 343,146 $ — Liabilities: Contingent consideration $ 7,984 $ — $ — $ 7,984 Total liabilities $ 7,984 $ — $ — $ 7,984 December 31, 2014 Assets: Cash and cash equivalents $ 347,845 $ 347,845 $ — $ — Marketable securities: U.S. government agency securities 131,536 — 131,536 — Certificates of deposit 12,622 — 12,622 — Total assets $ 492,003 $ 347,845 $ 144,158 $ — Liabilities: Contingent consideration $ 6,796 $ — $ — $ 6,796 Total liabilities $ 6,796 $ — $ — $ 6,796
Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations	The table below provides a roll-forward of fair value of the Company’s contingent consideration obligations, which include Level 3 inputs (in thousands): Six Months Ended June 30, 2015 Beginning balance $ 6,796 Additions — Changes in fair value 2,188 Reclassification to accrued expenses (1,000 ) Payments — Ending balance $ 7,984

Accrued expenses and other cu19

Accrued expenses and other current liabilities (Tables)	6 Months Ended
	Jun. 30, 2015
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): June 30, 2015 December 31, 2014 Employee compensation $ 3,937 $ 4,943 Accrued good and services 10,303 7,358 Accrued professional fees 1,090 428 Deferred rent, current portion 885 914 Contingent consideration, current portion 3,394 475 Other 415 531 Total accrued expenses and other current liabilities $ 20,024 $ 14,649

Stock-based compensation and 20

Stock-based compensation and warrants (Tables)	6 Months Ended
	Jun. 30, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Stock-Based Compensation Expense by Award Type	Stock-based compensation expense by award type was as follows (in thousands): Three months ended June 30, Six months ended June 30, 2015 2014 2015 2014 Stock options $ 15,310 $ 2,335 $ 20,065 $ 4,812 Restricted stock awards — 16 — 31 Restricted stock units 668 — 1,285 — Employee stock purchase plan 72 — 132 — $ 16,050 $ 2,351 $ 21,482 $ 4,843
Summary of Stock Option Activity Under Plan	The following table summarizes the stock option activity under the Company’s equity award plans (shares in thousands): Shares Weighted-average exercise price per share Outstanding at December 31, 2014 3,652 $ 12.30 Granted 915 $ 106.87 Exercised (671 ) $ 7.97 Canceled or forfeited (43 ) $ 44.68 Outstanding at June 30, 2015 3,853 $ 35.15 Exercisable at June 30, 2015 1,325 $ 7.89 Vested and expected to vest at June 30, 2015 3,776 $ 35.61
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Summary of Restricted Common Stock Awards	Restricted stock units The following table summarizes the restricted stock unit activity under the Company’s equity award plans (shares in thousands): Shares Weighted-average grant date fair value Unvested balance at December 31, 2014 179 $ 30.47 Granted 25 $ 179.30 Vested — — Forfeited (1 ) $ 30.47 Unvested balance at June 30, 2015 203 $ 48.77

Net loss per share (Tables)

Net loss per share (Tables)	6 Months Ended
	Jun. 30, 2015
Earnings Per Share [Abstract]
Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share	The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect (in thousands): Three and six months ended June 30, 2015 2014 Warrants 177 338 Outstanding stock options 3,853 4,112 Unvested restricted stock — 27 Restricted stock units 203 — ESPP shares 4 — Acquisition holdback 94 94 4,331 4,571

Description of the business - A

Description of the business - Additional Information (Detail) - Jun. 30, 2015 - USD ($) $ / shares in Units, $ in Thousands	Total	Total
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Stock issued during period, shares, new issues	2,941,176
Proceeds from public offering of common stock, net of issuance costs	$ 477,200	$ 477,179
Shares Issued, price per share	$ 170	$ 170
Underwriting discounts and commissions and estimated offering expenses	$ 22,800

Summary of significant accoun23

Summary of significant accounting policies and basis of presentation - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2015Segment
Accounting Policies [Abstract]
Number of operating segment	1

Marketable securities - Summary

Marketable securities - Summary of Available for Sale Securities Held (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 343,199	$ 144,229
Unrealized Gains	37	6
Unrealized Losses	(90)	(77)
Fair Value	343,146	144,158
U.S. Government Agency Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	329,359	131,589
Unrealized Gains	29	6
Unrealized Losses	(89)	(59)
Fair Value	329,299	131,536
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,840	12,640
Unrealized Gains	8
Unrealized Losses	(1)	(18)
Fair Value	$ 13,847	$ 12,622

Fair value measurements - Recor

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets:
Assets, fair value disclosure, recurring	$ 936,445	$ 492,003
Liabilities:
Liabilities, fair value disclosure, recurring	7,984	6,796
Contingent consideration obligations [Member]
Liabilities:
Liabilities, fair value disclosure, recurring	7,984	6,796
Cash and Cash Equivalents [Member]
Assets:
Assets, fair value disclosure, recurring	593,299	347,845
U.S. Government Agency Securities [Member]
Assets:
Assets, fair value disclosure, recurring	329,299	131,536
Certificates of Deposit [Member]
Assets:
Assets, fair value disclosure, recurring	13,847	12,622
Quoted prices in active markets (Level 1) [Member]
Assets:
Assets, fair value disclosure, recurring	593,299	347,845
Quoted prices in active markets (Level 1) [Member] | Cash and Cash Equivalents [Member]
Assets:
Assets, fair value disclosure, recurring	593,299	347,845
Significant other observable inputs (Level 2) [Member]
Assets:
Assets, fair value disclosure, recurring	343,146	144,158
Significant other observable inputs (Level 2) [Member] | U.S. Government Agency Securities [Member]
Assets:
Assets, fair value disclosure, recurring	329,299	131,536
Significant other observable inputs (Level 2) [Member] | Certificates of Deposit [Member]
Assets:
Assets, fair value disclosure, recurring	13,847	12,622
Significant unobservable inputs (Level 3) [Member]
Liabilities:
Liabilities, fair value disclosure, recurring	7,984	6,796
Significant unobservable inputs (Level 3) [Member] | Contingent consideration obligations [Member]
Liabilities:
Liabilities, fair value disclosure, recurring	$ 7,984	$ 6,796

Fair value measurements - Addit

Fair value measurements - Additional Information (Detail) - USD ($)	3 Months Ended	6 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents maturities		Three months or less
Realized gain (loss) on available-for-sale securities		$ 0
Reclassification out of accumulated other comprehensive income		0
Unrealized Loss on Securities		181,300,000	$ 134,400,000
Investments with other-than-temporary impairment		0	0
Contingent consideration, current		3,394,000	475,000
Contingent consideration, non current		4,590,000	$ 6,321,000
Pregenen [Member] | Scenario, Forecast [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Settlement of contingent consideration liability	$ 1,000,000
Stock Purchase Agreement [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration, current		1,000,000
Stock Purchase Agreement [Member] | Pregenen [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration, current		$ 1,000,000
Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Milestone achievement period		2,016
Milestone discount rates		10.50%
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Milestone achievement period		2,026
Milestone discount rates		14.70%

Fair value measurements - Roll-

Fair value measurements - Roll-Forward of Fair Value of the Company's Contingent Consideration Obligations (Detail) - Significant unobservable inputs (Level 3) [Member] - Contingent consideration obligations [Member] $ in Thousands	6 Months Ended
	Jun. 30, 2015USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 6,796
Changes in fair value	2,188
Reclassification to accrued expenses	(1,000)
Ending balance	$ 7,984

Accrued expenses and other cu28

Accrued expenses and other current liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Employee compensation	$ 3,937	$ 4,943
Accrued good and services	10,303	7,358
Accrued professional fees	1,090	428
Deferred rent, current portion	885	914
Contingent consideration, current	3,394	475
Other	415	531
Total accrued expenses and other current liabilities	$ 20,024	$ 14,649

Commitments and contingencies -

Commitments and contingencies - Additional Information (Detail) € in Millions	Jun. 29, 2015USD ($)ft²	Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2013EUR (€)	Jun. 30, 2015EUR (€)	Dec. 31, 2014USD ($)	Dec. 31, 2014EUR (€)	Jun. 30, 2014USD ($)
Commitments And Contingencies Disclosure [Line Items]
Other non-current assets			$ 1,511,000			$ 1,215,000
Contingent consideration liability, current			$ 3,394,000			$ 475,000
Lease starting on July 13, 2015
Commitments And Contingencies Disclosure [Line Items]
Lease office space | ft²	15,120
Lease starting date	Jul. 13, 2015
Yearly lease payments	$ 483,840
Operating lease description			Under the terms of the lease, the Company leased approximately 15,120 square feet starting on July 13, 2015 for $483,840 per year in base rent, which is subject to a 3% annual increase plus certain operating expenses and taxes.
Operating lease, rent increase percentage	3.00%
Lease starting on January 1,2016
Commitments And Contingencies Disclosure [Line Items]
Additional lease office space | ft²	8,075
Lease starting date	Jan. 1, 2016
Yearly lease payments	$ 258,400
Operating lease description			Under the terms of the lease, the Company will also lease an additional 8,075 square feet of office space in the same premises starting on January 1, 2016 for an additional $258,400 per year in base rent, which is subject to a 3% annual increase plus certain operating expenses and taxes.
Operating lease, rent increase percentage	3.00%
Stock Purchase Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent consideration liability, current			$ 1,000,000
Pregenen [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments								$ 134,000,000
Pregenen [Member] | Stock Purchase Agreement [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent consideration liability, current			$ 1,000,000
Pregenen [Member] | Preclinical Milestones [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments								14,000,000
Pregenen [Member] | Clinical Milestone Payments [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments								20,100,000
Pregenen [Member] | Commercial Milestones Payments [Member]
Commitments And Contingencies Disclosure [Line Items]
Contingent cash payments								$ 99,900,000
Pregenen [Member] | Scenario, Forecast [Member]
Commitments And Contingencies Disclosure [Line Items]
Settlement of contingent consideration liability		$ 1,000,000
French Credit d'Impot Recherche Program [Member]
Commitments And Contingencies Disclosure [Line Items]
Eligible percentage of research expense monetized			30.00%
Aggregate reimbursement received related to years 2011 through 2013 | €				€ 1.1
Current assets | €							€ 0.7
Other non-current assets | €					€ 0.3

Significant agreements - Additi

Significant agreements - Additional Information (Detail) - Celgene Corporation [Member]	Jun. 03, 2015USD ($)Deliverables	Mar. 19, 2013USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2014USD ($)	Dec. 31, 2014USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Term of collaboration agreement		3 years
First Product Candidates [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	$ 10,000,000
Additional Product Candidates [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	15,000,000
Co-Develop and Co-Promote Options not Exercise [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	10,000,000
Maximum [Member] | Clinical Milestone Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	10,000,000
Maximum [Member] | Regulatory Milestone Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	117,000,000
Maximum [Member] | Commercial Milestones Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	$ 78,000,000
Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of deliverable | Deliverables	3
Consideration allocated to agreement			$ 109,000,000
Deferred revenue recognition period			3 years
Deferred revenue recognized			$ 11,300,000	$ 12,500,000
Deferred revenue			44,400,000		$ 30,700,000
Deferred Revenue yet to be recognized			16,900,000
Collaborative Arrangement [Member] | Option Fee [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event			10,000,000
Collaborative Arrangement [Member] | Undelivered Elements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received			20,000,000
Collaborative Arrangement [Member] | Delivered Elements [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received			17,300,000
Collaborative Arrangement, Co-promotion and Development [Member] | Maximum [Member] | Clinical Milestone Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	$ 10,000,000
Collaborative Arrangement, Co-promotion and Development [Member] | Maximum [Member] | Regulatory Milestone Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	54,000,000
Collaborative Arrangement, Co-promotion and Development [Member] | Maximum [Member] | Commercial Milestones Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Amount per product eligible to be received upon achievement of specified event	36,000,000
Up-front Payment Arrangement [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received		$ 75,000,000	25,000,000
Up-front Payment Arrangement [Member] | Amended Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration agreement, cash payment received	$ 25,000,000
Manufacturing Services | Collaborative Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Consideration allocated to agreement			$ 54,100,000

Stock-based compensation and 31

Stock-based compensation and warrants - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 29, 2015	Jan. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increased number of issuance of awards under the 2013 Plan		1,300,000
Number of shares available for issuance			900,000		900,000
Stock-based compensation expense			$ 16,050	$ 2,351	$ 21,482	$ 4,843
Stock option share exercised					671,000
Proceed from option share exercised					$ 5,300
Warrants outstanding			200,000		200,000		200,000
Warrants exercised					0
Cancellation and expiration of warrants					0
Research And Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense			$ 6,700
Chief Scientific Officer | Research And Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Incremental value on option valuation	$ 3,000
Stock-based compensation expense			1,800		$ 2,800
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			80,500		$ 80,500
Expected weighted-average period related to unvested stock options, restricted stock awards and employee stock purchase plan					2 years 10 months 24 days
Stock-based compensation expense			15,310	$ 2,335	$ 20,065	$ 4,812
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			80,500		$ 80,500
Expected weighted-average period related to unvested stock options, restricted stock awards and employee stock purchase plan					2 years 10 months 24 days
Stock-based compensation expense			668		$ 1,285
Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock- based compensation expense related to unvested stock options, restricted stock awards and employee stock purchase plan			$ 80,500		$ 80,500
Expected weighted-average period related to unvested stock options, restricted stock awards and employee stock purchase plan					2 years 10 months 24 days
Common shares reserved for future issuance			238,000		238,000
Shares purchased under the plan		6,780

Stock-based compensation and 32

Stock-based compensation and warrants - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 16,050	$ 2,351	$ 21,482	$ 4,843
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	15,310	2,335	20,065	4,812
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 16		$ 31
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	668		1,285
Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 72		$ 132

Stock-based compensation and 33

Stock-based compensation and warrants - Summary of Restricted Stock Units(Detail) - 6 months ended Jun. 30, 2015 - Restricted Stock Units [Member] - $ / shares shares in Thousands	Total
Shares
Unvested balance at beginning of period	179
Granted	25
Forfeited	(1)
Unvested balance at end of period	203
Weighted-average grant date fair value
Unvested balance at beginning of period	$ 30.47
Granted	179.30
Forfeited	30.47
Unvested balance at end of period	$ 48.77

Stock-based compensation and 34

Stock-based compensation and warrants - Summary of Stock Option Activity Under Plan (Detail) - Jun. 30, 2015 - $ / shares shares in Thousands	Total
Shares
Outstanding at beginning of period	3,652
Granted	915
Exercised	(671)
Canceled or forfeited	(43)
Outstanding at end of period	3,853
Exercisable at end of period	1,325
Vested and expected to vest at end of period	3,776
Weighted-average exercise price per share
Outstanding at beginning of period	$ 12.30
Granted	106.87
Exercised	7.97
Canceled or forfeited	44.68
Outstanding at end of period	35.15
Exercisable at end of period	7.89
Vested and expected to vest at end of period	$ 35.61

Income taxes - Additional Infor

Income taxes - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Current deferred tax asset	$ 399	$ 1,913
Non-current deferred tax liability	$ 399	$ 1,913

Net loss per share - Common Sto

Net loss per share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	4,331	4,571
Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	177	338
Outstanding stock options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	3,853	4,112
Restricted Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share		27
Restricted Stock Units R S U [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	203
Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	4
Acquisition holdback [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share	94	94