0001293971-22-000034 | 10-Q | XBRL Viewer

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Stock-based compensation - Summary of Restricted Stock Units (Detail) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2022 $ / shares shares
Shares (in thousands)
Unvested balance at beginning of period (in shares) \| shares	3,193
Granted (in shares) \| shares	1,291
Vested (in shares) \| shares	(238)
Forfeited (in shares) \| shares	(340)
Unvested balance at end of period (in shares) \| shares	3,906
Weighted- average grant date fair value
Unvested balance at beginning of period (in dollars per share) \| $ / shares	$ 16.21
Granted (in dollars per share) \| $ / shares	7.85
Vested (in dollars per share) \| $ / shares	26.67
Forfeited (in dollars per share) \| $ / shares	14.79
Unvested balance at end of period (in dollars per share) \| $ / shares	$ 12.96

Discontinued operations (Tables)

3 Months Ended

Mar. 31, 2022

Discontinued Operations and Disposal Groups [Abstract]

Summary of Revenues , Expenses, Non-cash Items and Capital Expenditures for Discontinued Operations

The following table summarizes revenue and expenses of the discontinued operations for the three months ended March 31, 2021 (in thousands):


	Three months ended March 31, 2021
Revenue:
Service revenue	$	5,918
Collaborative arrangement revenue	1,519
Royalty and other revenue	4,463
Total revenues	11,900
Operating expenses:
Research and development	71,635
Selling, general and administrative	23,305
Cost of royalty and other revenue	1,705
Change in fair value of contingent consideration	369
Total operating expenses	97,014
Loss from operations	(85,114)
Interest income, net	355
Other income, net	455
Loss before income taxes	(84,304)
Income tax benefit (expense)	—
Net loss	$	(84,304)

The following table summarizes the significant non-cash items and capital expenditures of the discontinued operations that are included in the condensed consolidated statements of cash flows for the three months ended March 31, 2021 (in thousands):


	Three months ended March 31, 2021
Operating activities:
Change in fair value of contingent consideration	$	369
Depreciation and amortization	3,800
Stock-based compensation expense	11,181

Investing activities:
Purchase of property, plant and equipment	$	(6,173)

Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	$	1,954

- Definition

Tabular disclosure of information related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component.

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+ Details

Accrued expenses and other current liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Payables and Accruals [Abstract]
Accrued manufacturing costs	$ 30,806	$ 15,722
Accrued goods and services	19,119	24,273
Accrued clinical and contract research organization costs	18,628	17,769
Accrued employee compensation	15,744	41,095
Accrued professional fees	1,674	1,665
Deferred revenue, current portion	1,822	2,282
Other	1,239	1,152
Accrued Liabilities and Other Liabilities, Total	$ 89,032	$ 103,958

Fair value measurements - Recorded Amount of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets:
Marketable securities:	$ 160,377	$ 235,456
Equity securities	1,182	3,691
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	106,260	161,160
Equity securities	1,182	3,691
Total	266,637	396,617
Fair Value, Measurements, Recurring \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	115,705	128,393
Fair Value, Measurements, Recurring \| Corporate bonds
Assets:
Marketable securities:	33,667	49,308
Fair Value, Measurements, Recurring \| Commercial paper
Assets:
Marketable securities:	9,823	54,065
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1)
Assets:
Cash and cash equivalents	106,260	161,146
Equity securities	1,182	3,691
Total	107,442	164,837
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1) \| Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1) \| Commercial paper
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2)
Assets:
Cash and cash equivalents	0	14
Equity securities	0	0
Total	159,195	231,780
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	115,705	128,393
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Assets:
Marketable securities:	33,667	49,308
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2) \| Commercial paper
Assets:
Marketable securities:	9,823	54,065
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Equity securities	0	0
Total	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| U.S. government agency securities and treasuries
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Corporate bonds
Assets:
Marketable securities:	0	0
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3) \| Commercial paper
Assets:
Marketable securities:	$ 0	$ 0

Stock-based compensation - Summary of Stock-Based Compensation Expense by Award Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 12,390	$ 31,294
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,260	16,426
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	7,034	10,217
Employee stock purchase plan and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 96	$ 4,651

Leases	3 Months Ended
Leases	Mar. 31, 2022
Leases [Abstract]
Leases	Leases The Company leases certain office and laboratory space, primarily located in Cambridge, Massachusetts and Somerville, Massachusetts. Additionally, the Company has embedded leases through its agreements with contract manufacturing organizations in both the United States and internationally. Except as described below, there have been no material changes in lease obligations from those disclosed in Note 10 to the consolidated financial statements included in the Company's 2021 Annual Report on Form 10-K. Assembly Row lease In November 2021, the Company entered into a lease agreement with Assembly Row 5B, LLC ("Landlord") for office space located at 455 Grand Union Boulevard in Somerville, Massachusetts to serve as the Company's future corporate headquarters (the “Assembly Row Lease”). Upon signing the Assembly Row Lease, the Company executed a $2.8 million letter of credit for the Landlord’s benefit, which is classified as restricted cash and other non-current assets on the Company’s condensed consolidated balance sheets. In March 2022, the Assembly Row Lease commenced upon the Landlord granting the Company control of the leased premises. The Assembly Row Lease will continue until December 31, 2032, with an option to extend for two additional five-year terms. The Company classified the Assembly Row Lease as an operating lease and recognized a right-of-use asset and lease liability upon lease commencement. The Company will recognize rent expense on a straight-line basis throughout the remaining term of the Assembly Row Lease. 50 Binney Street lease & sublease In April 2019, the Company entered into an agreement to lease office space located at 50 Binney Street in Cambridge, Massachusetts (the “50 Binney Street Lease”). In December 2021, the Company entered into an agreement to sublease the entire office space to Meta Platforms, Inc. (“Meta”) (the "Sublease"). In April 2022, both the 50 Binney Street Lease and the Sublease commenced upon the landlord granting access to the leased premises. In connection with the execution of the 50 Binney Street Lease, the Company also entered into a purchase agreement with the landlord for furniture and equipment (the “Furniture Purchase Agreement”) located on the premises upon lease commencement. Upon execution of the Furniture Purchase Agreement, the Company made an upfront payment of $7.5 million. Upon lease commencement, the Company paid the remaining $7.25 million due under the Furniture Purchase Agreement. The Company is currently assessing the lease classification of the 50 Binney Street Lease. The Sublease will continue until December 31, 2030. The Company will earn rental income through its role as a lessor throughout the term of the Sublease.

Income taxes	3 Months Ended
Income taxes	Mar. 31, 2022
Income Tax Disclosure [Abstract]
Income taxes	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 tax expense recognized during the three months ended March 31, 2022 is immaterial due to the wind down of our operations in Europe. In March 2021, the American Rescue Plan Act (“ARPA”) was enacted and contained extenders to the refundable employee retention credit and provided further limitations to executive compensation effective for tax years beginning after 2026. The Company has concluded that the provisions in the CARES Act, Consolidated Appropriations Act, and ARPA have an immaterial impact on the Company’s income tax expense due to its cumulative losses and full valuation allowance position.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

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+ Details

Stock-based compensation

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Stock-based compensation

In January 2022 and 2021, the number of shares of common stock available for issuance under the 2013 Stock Option and Incentive Plan (“2013 Plan”) was increased by approximately 2.8 million and 2.7 million shares, respectively, as a result of the automatic increase provision of the 2013 Plan. As of March 31, 2022, the total number of shares of common stock available for issuance under the 2013 Plan was approximately 4.1 million.

Stock-based compensation expense

The Company recognized stock-based compensation expense totaling $12.4 million and $31.3 million during the three months ended March 31, 2022 and 2021, respectively. Stock-based compensation expense recognized by award type is included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended March 31,
	2022		2021(1)
Stock options	$	5,260	$	16,426
Restricted stock units	7,034		10,217
Employee stock purchase plan and other	96		4,651
	$	12,390	$	31,294

(1) Prior period amounts have been retrospectively adjusted to reflect the effects of the Separation.

Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended March 31,
	2022		2021(1)
Research and development	$	6,555	$	12,390
Selling, general and administrative	5,835		18,904
	$	12,390	$	31,294

(1) Prior period amounts have been retrospectively adjusted to reflect the effects of the Separation.

As of March 31, 2022, the Company had approximately $97.5 million of unrecognized stock-based compensation expense related to unvested stock options and restricted stock units (exclusive of those with service and performance conditions that have not yet been achieved), which is expected to be recognized over a weighted-average period of approximately 2.2 years.

Stock options

The following table summarizes the stock option activity under the Company’s equity award plans:


	Shares (in thousands)	Weighted- average exercise price per share
Outstanding at December 31, 2021	3,586	$	39.23
Granted	890	$	7.79
Exercised	(1)	$	1.04
Canceled or forfeited	(735)	$	58.27
Outstanding at March 31, 2022	3,740	$	29.14
Exercisable at March 31, 2022	1,406	$	52.80
Vested and expected to vest at March 31, 2022	3,740	$	29.14

During the three months ended March 31, 2022, less than 0.1 million stock options were exercised, resulting in total proceeds to the Company of less than $0.1 million.

Restricted stock units

The following table summarizes the restricted stock unit activity under the Company’s equity award plans:


	Shares (in thousands)	Weighted- average grant date fair value
Unvested at December 31, 2021	3,193	$	16.21
Granted	1,291	$	7.85
Vested	(238)	$	26.67
Forfeited	(340)	$	14.79
Unvested at March 31, 2022	3,906	$	12.96

Employee stock purchase plan

In June 2013, the Company adopted its 2013 Employee Stock Purchase Plan (“2013 ESPP”), which authorized the initial issuance of up to a total of 0.2 million shares of the Company’s common stock to participating employees. In June 2021, the Company amended the 2013 ESPP to authorize an additional 1.4 million shares of the Company’s common stock available to participating employees. During the three months ended March 31, 2022 and 2021, no shares and less than 0.1 million shares, respectively, of common stock were issued under the 2013 ESPP.

Marketable securities - Summary of Marketable Securities Held (Detail) - USD ($)	Mar. 31, 2022	Dec. 31, 2021
Amortized cost / Cost
Equity securities	$ 4,305,000	$ 4,305,000
Marketable securities	165,660,000	236,638,000
Unrealized gains
Equity securities	0	0
Marketable securities	0	0
Unrealized losses
Equity securities	(3,123,000)	(614,000)
Marketable securities	(5,283,000)	(1,182,000)
Fair value
Equity securities	1,182,000	3,691,000
Marketable securities	160,377,000	235,456,000
Debt securities, available-for-sale, noncurrent	0	0
U.S. government agency securities and treasuries
Amortized cost / Cost
Debt securities	117,730,000	128,902,000
Unrealized gains
Debt securities	0	0
Unrealized losses
Debt securities	(2,025,000)	(509,000)
Fair value
Debt securities	115,705,000	128,393,000
Corporate bonds
Amortized cost / Cost
Debt securities	33,802,000	49,366,000
Unrealized gains
Debt securities	0	0
Unrealized losses
Debt securities	(135,000)	(59,000)
Fair value
Debt securities	33,667,000	49,307,000
Commercial paper
Amortized cost / Cost
Debt securities	9,823,000	54,065,000
Unrealized gains
Debt securities	0	0
Unrealized losses
Debt securities	0	0
Fair value
Debt securities	$ 9,823,000	$ 54,065,000

Accrued expenses and other current liabilities (Tables)

3 Months Ended

Mar. 31, 2022

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

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


	As of March 31, 2022		As of December 31, 2021
Accrued manufacturing costs	$	30,806	$	15,722
Accrued goods and services	19,119		24,273
Accrued clinical and contract research organization costs	18,628		17,769
Accrued employee compensation	15,744		41,095
Accrued professional fees	1,674		1,665
Deferred revenue, current portion	1,822		2,282
Other	1,239		1,152
Total accrued expenses and other current liabilities	$	89,032	$	103,958

Discontinued operations - Revenue and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net loss	$ 0	$ (84,304)
2seventy bio \| Discontinued Operations, Disposed of by Means Other than Sale, Spinoff
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues		11,900
Research and development		71,635
Selling, general and administrative		23,305
Change in fair value of contingent consideration		369
Total operating expenses		97,014
Loss from operations		(85,114)
Interest income, net		355
Other income, net		455
Loss before income taxes		(84,304)
Income tax benefit (expense)		0
Net loss		(84,304)
2seventy bio \| Discontinued Operations, Disposed of by Means Other than Sale, Spinoff \| Service revenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues		5,918
2seventy bio \| Discontinued Operations, Disposed of by Means Other than Sale, Spinoff \| Collaborative arrangement revenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues		1,519
2seventy bio \| Discontinued Operations, Disposed of by Means Other than Sale, Spinoff \| Other revenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenues		4,463
Cost of royalty and other revenue		$ 1,705

Condensed Consolidated Balance Sheets (unaudited) - (Parenthetical) - $ / shares	Mar. 31, 2022	Dec. 31, 2021
Stockholders’ equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	125,000,000	125,000,000
Common stock, shares issued (in shares)	71,438,000	71,115,000
Common stock, shares outstanding (in shares)	71,438,000	71,115,000

Subsequent Events (Details) - Subsequent Event - April 2022 Reduction	1 Months Ended
	Apr. 30, 2022 USD ($)
Subsequent Event [Line Items]
Anticipated cost savings associated with restructuring	$ 160,000,000
Anticipated cost savings associated with restructuring, period of recognition	2 years
Plans to reduce workforce, as a percent	30.00%
Restructuring charges	$ 10,000,000

Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2020		66,432
Beginning balance at Dec. 31, 2020	$ 1,355,056	$ 665	$ 4,260,443	$ (5,505)	$ (2,900,547)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		294
Vesting of restricted stock units	0	$ 3	(3)
Exercise of stock options (in shares)		207
Exercise of stock options	1,219	$ 2	1,217
Purchase of common stock under ESPP (in shares)		67
Purchase of common stock under ESPP	1,707	$ 1	1,706
Stock-based compensation	36,090		36,090
Issuance of unrestricted stock awards to settle accrued employee compensation (in shares)		422
Issuance of unrestricted stock awards to settle accrued employee compensation	12,013	$ 4	12,009
Other comprehensive income	56			56
Net loss	(205,808)				(205,808)
Ending balance, shares (in shares) at Mar. 31, 2021		67,422
Ending balance at Mar. 31, 2021	$ 1,200,333	$ 675	4,311,462	(5,449)	(3,106,355)
Beginning balance (in shares) at Dec. 31, 2021	71,115	71,115
Beginning balance at Dec. 31, 2021	$ 374,277	$ 711	4,096,402	(2,911)	(3,719,925)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		310
Vesting of restricted stock units	$ 0	$ 3	(3)
Exercise of stock options (in shares)	1	1
Exercise of stock options	$ 1		1
Stock-based compensation	12,681		12,681
Issuance of unrestricted stock awards to settle accrued employee compensation (in shares)		12
Other comprehensive income	(1,548)			(1,548)
Net loss	$ (122,152)				(122,152)
Ending balance, shares (in shares) at Mar. 31, 2022	71,438	71,438
Ending balance at Mar. 31, 2022	$ 263,259	$ 714	$ 4,109,081	$ (4,459)	$ (3,842,077)

Property, plant and equipment, net (Tables)

3 Months Ended

Mar. 31, 2022

Property, Plant and Equipment [Abstract]

Summary of Property, Plant and Equipment Net

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


	As of March 31, 2022		As of December 31, 2021
Laboratory equipment	$	28,939	$	29,061
Computer equipment and software	421		421
Office equipment	117		117
Leasehold improvements	12		12
Construction-in-progress	2,957		501
Total property, plant and equipment	32,446		30,112
Less accumulated depreciation and amortization	(21,212)		(20,406)
Property, plant and equipment, net	$	11,234	$	9,706

Stock-based compensation (Tables)

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Summary of Stock-Based Compensation Expense by Award Type

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


	For the three months ended March 31,
	2022		2021(1)
Stock options	$	5,260	$	16,426
Restricted stock units	7,034		10,217
Employee stock purchase plan and other	96		4,651
	$	12,390	$	31,294

(1) Prior period amounts have been retrospectively adjusted to reflect the effects of the Separation.

Schedule of Stock-Based Compensation Expense by Classification

Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended March 31,
	2022		2021(1)
Research and development	$	6,555	$	12,390
Selling, general and administrative	5,835		18,904
	$	12,390	$	31,294

(1) Prior period amounts have been retrospectively adjusted to reflect the effects of the Separation.

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)	Weighted- average exercise price per share
Outstanding at December 31, 2021	3,586	$	39.23
Granted	890	$	7.79
Exercised	(1)	$	1.04
Canceled or forfeited	(735)	$	58.27
Outstanding at March 31, 2022	3,740	$	29.14
Exercisable at March 31, 2022	1,406	$	52.80
Vested and expected to vest at March 31, 2022	3,740	$	29.14

Summary of Restricted Common Stock Awards

The following table summarizes the restricted stock unit activity under the Company’s equity award plans:


	Shares (in thousands)	Weighted- average grant date fair value
Unvested at December 31, 2021	3,193	$	16.21
Granted	1,291	$	7.85
Vested	(238)	$	26.67
Forfeited	(340)	$	14.79
Unvested at March 31, 2022	3,906	$	12.96

Property, plant and equipment, net

3 Months Ended

Mar. 31, 2022

Property, Plant and Equipment [Abstract]

Property, plant and equipment, net

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


	As of March 31, 2022		As of December 31, 2021
Laboratory equipment	$	28,939	$	29,061
Computer equipment and software	421		421
Office equipment	117		117
Leasehold improvements	12		12
Construction-in-progress	2,957		501
Total property, plant and equipment	32,446		30,112
Less accumulated depreciation and amortization	(21,212)		(20,406)
Property, plant and equipment, net	$	11,234	$	9,706

Stock-based compensation - Schedule of Stock-Based Compensation Expense by Classification (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 12,390	$ 31,294
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	6,555	12,390
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5,835	$ 18,904

Condensed Consolidated Balance Sheets (unaudited) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 106,260	$ 161,160
Marketable securities	105,328	138,343
Prepaid expenses	31,798	25,628
Receivables and other current assets	11,531	11,389
Total current assets	254,917	336,520
Marketable securities	55,049	97,114
Property, plant and equipment, net	11,234	9,706
Goodwill	5,646	5,646
Operating lease right-of-use assets	111,897	91,532
Restricted cash and other non-current assets	52,328	53,277
Total assets	491,071	593,795
Current liabilities:
Accounts payable	28,350	25,883
Accrued expenses and other current liabilities	89,032	103,958
Operating lease liability, current portion	25,510	23,152
Total current liabilities	142,892	152,993
Operating lease liability, net of current portion	84,828	66,432
Other non-current liabilities	92	93
Total liabilities	227,812	219,518
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.01 par value, 5,000 shares authorized; 0 shares issued and outstanding at March 31, 2022 and December 31, 2021	0	0
Common stock, $0.01 par value, 125,000 shares authorized; 71,438 and 71,115 shares issued and outstanding at March 31, 2022 and December 31, 2021, respectively	714	711
Additional paid-in capital	4,109,081	4,096,402
Accumulated other comprehensive loss	(4,459)	(2,911)
Accumulated deficit	(3,842,077)	(3,719,925)
Total stockholders’ equity	263,259	374,277
Total liabilities and stockholders’ equity	$ 491,071	$ 593,795

Discontinued operations - Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($) $ / shares	Nov. 04, 2021 $ / shares	Nov. 03, 2021 agreement	Sep. 30, 2021 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Conversion ratio			0.3333
Common stock, par value (in dollars per share) \| $ / shares	$ 0.01	$ 0.01	$ 0.01
Number of transition services agreements \| agreement				2
Initial term of transition services agreement				2 years
Lentiviral Vector Manufacturing Facility
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net assets transferred to 2seventy bio					$ 111.2
Loss on fixed assets disposal		$ 2.0
2seventy bio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock, par value (in dollars per share) \| $ / shares			$ 0.0001
Selling, general and administrative expense related to transition services agreement	$ 3.1
Accounts receivable due from related party	3.0
Accounts payable to related party	5.3
2seventy bio \| 60 Binney Street Lease
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Related party expense	$ 1.1

Subsequent events	3 Months Ended
Subsequent events	Mar. 31, 2022
Subsequent Events [Abstract]
Subsequent events	Subsequent events April 2022 reduction in workforce In April 2022, the Board of Directors of the Company approved a comprehensive restructuring plan intended to reduce operating expenses. The Company intends to maintain targeted research efforts focused on in-vivo LVV gene therapy and to deprioritize direct investments in reduced toxicity conditioning and cryopreserved apheresis. The restructuring is anticipated to produce up to $160 million in cost savings over the next two years. As part of the restructuring, the Company plans to reduce its workforce by 30% across the second and third quarters of 2022. The Company estimates that it will incur approximately $10 million in costs to implement the restructuring, comprised primarily of severance payments and continuing health care coverage over the severance period. The restructuring actions associated with these charges commenced in April 2022 and be substantially completed by the end of 2022.

Discontinued operations

3 Months Ended

Mar. 31, 2022

Discontinued Operations and Disposal Groups [Abstract]

Discontinued operations

Sale of bluebird Research Triangle manufacturing facility

In November 2017, the Company acquired a manufacturing facility in Durham, North Carolina ("bRT") for the future manufacture of LVV for the Company’s therapies related to its oncology programs. In July 2021, the Company and Resilience US, Inc., an affiliate of National Resilience, Inc. ("Resilience"), signed an Asset Purchase Agreement (the “Agreement”). As part of the Agreement, and upon the closing of the transaction in September 2021, Resilience acquired the Company's LVV manufacturing facility located in Durham, North Carolina and retained staff currently employed at the site. As a result of the

transaction, the Company disposed of $111.2 million of net assets, primarily consisting of the building and laboratory equipment associated with the Company's oncology programs. The Company recognized a loss on disposal of assets of $2.0 million during the year ended December 31, 2021. As the sale of the bRT manufacturing facility and the separation of 2seventy bio (as described below) were deemed to represent multiple components of a single disposal plan, the results of operations related to bRT have been included as a component of discontinued operations.

2seventy bio Separation

On November 4, 2021, the Company completed the previously announced separation of its oncology programs and portfolio, and the certain related assets and liabilities, into a separate, independent publicly traded company (the “Separation”). The Separation was effected by means of a distribution of all of the outstanding shares of common stock of 2seventy bio in which each bluebird stockholder received one share of common stock, par value $0.0001 per share, of 2seventy bio for every three shares of common stock, par value $0.01 per share, of bluebird held as of the close of business on October 19, 2021 (the “Distribution”).

In connection with the Separation, bluebird entered into a separation agreement (the “Separation Agreement”) with 2seventy bio, dated as of November 3, 2021, that, among other things, set forth bluebird’s agreements with 2seventy bio regarding the principal actions to be taken in connection with the Separation, including the Distribution. The effective time of the Distribution was 12:01 a.m. on November 4, 2021. The Separation Agreement identified assets transferred to, liabilities assumed by and contracts assigned to 2seventy bio as part of the Separation, and it provided for when and how these transfers, assumptions and assignments occurred. The purpose of the Separation Agreement was to provide 2seventy bio and bluebird with assets to operate their respective businesses and retain or assume liabilities related to those assets. Each of 2seventy bio and bluebird agreed to releases, with respect to pre-Separation claims, and cross indemnities, with respect to post-Separation claims, that were principally designed to place financial responsibility for the obligations and liabilities allocated to 2seventy bio under the Separation Agreement with 2seventy bio and financial responsibility for the obligations and liabilities allocated to bluebird under the Separation Agreement with bluebird. bluebird and 2seventy bio are also each subject to mutual 12-month employee non-solicit and non-hire restrictions, subject to certain customary exceptions.

bluebird and 2seventy bio also entered into a tax matters agreement, an employee matters agreement and an intellectual property agreement. Additionally, bluebird entered into two transition services agreements with 2seventy bio, whose President is a member of the Company’s Board of Directors. Pursuant to the transition service agreements, bluebird is obligated to provide and is entitled to receive certain transition services related to corporate functions, such as finance, human resources, internal audit, research and development, financial reporting, and information technology. Services provided by bluebird to 2seventy bio will continue for an initial term of up to two years, unless earlier terminated or extended according to the terms of the transition services agreement. Services received and performed are paid at a mutually agreed upon rate. Amounts received for services provided to 2seventy bio are recorded as other income and amounts paid for services provided by 2seventy bio are recorded as selling, general and administrative expense and research and development expense, as applicable. In addition, the Company entered into a sublease agreement with 2seventy bio for office, laboratory and storage space located at 60 Binney Street (the "60 Binney Street Sublease") while it constructs and outfits its new office and laboratory space.

During the three months ended March 31, 2022, the Company incurred $3.1 million of net expense for transactions with 2seventy bio within research and development and selling, general and administrative expense in the condensed consolidated statements of operations and comprehensive loss, including $1.1 million of net expense related to the 60 Binney Street Sublease. As of March 31, 2022, the Company had $3.0 million of accounts receivable due from and $5.3 million of accounts payable due to 2seventy bio. As of December 31, 2021, the Company had an immaterial amount of accounts receivable and accounts payable due from and due to 2seventy bio.

Discontinued operations

In connection with the Separation, the Company determined its oncology business, together with the bRT manufacturing facility, qualified for discontinued operations accounting treatment in accordance with ASC 205-20. The following table summarizes revenue and expenses of the discontinued operations for the three months ended March 31, 2021 (in thousands):


	Three months ended March 31, 2021
Revenue:
Service revenue	$	5,918
Collaborative arrangement revenue	1,519
Royalty and other revenue	4,463
Total revenues	11,900
Operating expenses:
Research and development	71,635
Selling, general and administrative	23,305
Cost of royalty and other revenue	1,705
Change in fair value of contingent consideration	369
Total operating expenses	97,014
Loss from operations	(85,114)
Interest income, net	355
Other income, net	455
Loss before income taxes	(84,304)
Income tax benefit (expense)	—
Net loss	$	(84,304)

There were no revenue and expenses of the discontinued operations for the three months ended March 31, 2022, as all operations were transferred to 2seventy bio upon the Separation. There were no assets and liabilities related to discontinued operations as of March 31, 2022 or December 31, 2021, as all balances were transferred to 2seventy bio upon the Separation.


	Three months ended March 31, 2021
Operating activities:
Change in fair value of contingent consideration	$	369
Depreciation and amortization	3,800
Stock-based compensation expense	11,181

Investing activities:
Purchase of property, plant and equipment	$	(6,173)

Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	$	1,954

Leases - Narrative (Details) $ in Thousands	1 Months Ended
Leases - Narrative (Details) $ in Thousands	Mar. 31, 2022 renewalOption	Nov. 30, 2021 USD ($)	Apr. 30, 2022 USD ($)
Assembly Row Lease
Lessee, Lease, Description [Line Items]
Number of lease renewal options \| renewalOption	2
Lease renewal term	5 years
Collateralized letter of credit		$ 2,800
50 Binney Street Sublease \| Subsequent Event
Lessee, Lease, Description [Line Items]
Upfront payment for purchase of furniture and equipment			$ 7,500
Payment for purchase of furniture and equipment, upon lease commencement			$ 7,250

Fair value measurements

3 Months Ended

Mar. 31, 2022

Fair Value Disclosures [Abstract]

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 March 31, 2022 and December 31, 2021 (in thousands):


Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
March 31, 2022
Assets:
Cash and cash equivalents	$	106,260	$	106,260	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	115,705		—		115,705		—
Corporate bonds	33,667		—		33,667		—
Commercial paper	9,823		—		9,823		—
Equity securities	1,182		1,182		—		—
Total	$	266,637	$	107,442	$	159,195	$	—
December 31, 2021
Assets:
Cash and cash equivalents	$	161,160	$	161,146	$	14	$	—
Marketable securities:
U.S. government agency securities and treasuries	128,393		—		128,393		—
Corporate bonds	49,308		—		49,308		—
Commercial paper	54,065		—		54,065		—
Equity securities	3,691		3,691		—		—
Total	$	396,617	$	164,837	$	231,780	$	—

Cash and cash equivalents

The Company considers all highly liquid securities with original final maturities of 90 days or less from the date of purchase to be cash equivalents. As of March 31, 2022 and December 31, 2021, cash and cash equivalents comprise funds in cash and money market accounts.

Marketable securities

Marketable securities classified as Level 2 within the valuation hierarchy generally consist of U.S. government agency securities and treasuries, corporate bonds, and commercial paper. The Company estimates the fair values of these marketable securities by taking into consideration valuations obtained from third-party pricing sources. These pricing sources utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include market pricing based on real-time trade data for the same or similar securities, issuer credit spreads, benchmark yields, and other observable inputs. The Company validates the prices provided by its third-party pricing sources by understanding the models used, obtaining market values from other pricing sources and analyzing pricing data in certain instances.

The amortized cost of available-for-sale debt securities is adjusted for amortization of premiums and accretion of discounts to the earliest call date for premiums or to maturity for discounts. At March 31, 2022 and December 31, 2021, the balance in the Company’s accumulated other comprehensive loss was composed primarily of activity related to the Company’s available-for-sale debt securities. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale debt securities during the three months ended March 31, 2022 or 2021.

Accrued interest receivable on the Company's available-for-sale debt securities totaled $0.3 million and $0.3 million as of March 31, 2022 and December 31, 2021, respectively. No accrued interest receivable was written off during the three months ended March 31, 2022 or 2021.

The following table summarizes available-for-sale debt securities in a continuous unrealized loss position for less than and greater than twelve months, and for which an allowance for credit losses has not been recorded at March 31, 2022 and December 31, 2021 (in thousands):


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2022
U.S. government agency securities and treasuries	$	113,225	$	(2,005)	$	2,480	$	(20)	$	115,705	$	(2,025)
Corporate bonds	30,417		(135)		—		—		30,417		(135)
Total	$	143,642	$	(2,140)	$	2,480	$	(20)	$	146,122	$	(2,160)
December 31, 2021
U.S. government agency securities and treasuries	$	108,695	$	(505)	$	2,496	$	(4)	$	111,191	$	(509)
Corporate bonds	45,042		(56)		3,896		(2)		48,938		(58)
Total	$	153,737	$	(561)	$	6,392	$	(6)	$	160,129	$	(567)

The Company determined that there was no material change in the credit risk of the above investments during the three months ended March 31, 2022. As such, an allowance for credit losses was not recognized. As of March 31, 2022, the Company does not intend to sell such securities, however, the Company determined that it is more likely than not that the Company will be required to sell certain securities before recovery of their amortized cost bases. The Company determined that the impact of this assessment was immaterial. Subsequently, in April 2022, the Company sold securities with a carrying value of $29.7 million and realized net aggregate losses of $0.4 million.

The Company held equity securities with an aggregate fair value of $1.2 million and $3.7 million as of March 31, 2022 and December 31, 2021, respectively, within current marketable securities on its condensed consolidated balance sheets. In January 2021, the Company sold a portion of its equity securities for proceeds of $31.3 million. During the three months ended March 31, 2022 and 2021, the Company recorded a loss of $2.5 million and a gain of $28.4 million, respectively, related to its equity securities. Gains and losses related to equity securities are included in other (expense) income, net in the condensed consolidated statements of operations and comprehensive loss.

Please refer to Note 9, Commitments and contingencies, for further information.

- Definition

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

+ References + Details

Net loss per share - Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	9,962	9,415
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	5,645	6,458
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	4,053	2,073
ESPP shares and other
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted net loss per share (in shares)	264	884

Marketable securities (Tables)

3 Months Ended

Mar. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Summary of Marketable Securities Held

The following table summarizes the marketable securities held at March 31, 2022 and December 31, 2021 (in thousands):


Description	Amortized cost / Cost		Unrealized gains		Unrealized losses		Fair value
March 31, 2022
U.S. government agency securities and treasuries	$	117,730	$	—	$	(2,025)	$	115,705
Corporate bonds	33,802		—		(135)		33,667
Commercial paper	9,823		—		—		9,823
Equity securities	4,305		—		(3,123)		1,182
Total	$	165,660	$	—	$	(5,283)	$	160,377
December 31, 2021
U.S. government agency securities and treasuries	$	128,902	$	—	$	(509)	$	128,393
Corporate bonds	49,366		—		(59)		49,307
Commercial paper	54,065		—		—		54,065
Equity securities	4,305		—		(614)		3,691
Total	$	236,638	$	—	$	(1,182)	$	235,456

Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash flows from operating activities:
Net loss	$ (122,152)	$ (205,808)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	0	369
Depreciation and amortization	1,014	5,360
Stock-based compensation expense	12,390	42,527
Loss (gain) on equity securities	2,508	(28,372)
Excess inventory reserve	7,519	0
Other non-cash items	189	2,513
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(13,059)	(16,082)
Operating lease right-of-use assets	6,517	8,098
Accounts payable	2,467	67
Accrued expenses and other liabilities	(16,561)	(2,693)
Operating lease liabilities	(6,128)	(9,306)
Net cash used in operating activities	(125,296)	(203,327)
Cash flows from investing activities:
Purchase of property, plant and equipment	(857)	(7,626)
Purchases of marketable securities	0	(53,200)
Proceeds from maturities of marketable securities	70,783	350,860
Proceeds from sales of marketable securities	0	31,318
Net cash provided by investing activities	69,926	321,352
Cash flows from financing activities:
Proceeds from exercise of stock options and ESPP contributions	9	3,796
Net cash provided by financing activities	9	3,796
(Decrease) increase in cash, cash equivalents and restricted cash	(55,361)	121,821
Cash, cash equivalents and restricted cash at beginning of period	206,693	373,728
Cash, cash equivalents and restricted cash at end of period	151,332	495,549
Reconciliation of cash, cash equivalents and restricted cash:
Cash and cash equivalents	106,260	439,714
Restricted cash included in receivables and other current assets	1,822	1,330
Restricted cash included in restricted cash and other non-current assets	43,250	54,505
Total cash, cash equivalents and restricted cash	151,332	495,549
Supplemental cash flow disclosures from investing and financing activities:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	2,134	2,238
Right-of-use assets obtained in exchange for operating lease liabilities	26,882	22,049
Issuance of unrestricted stock awards to settle accrued employee compensation	$ 0	$ 12,013

Accrued expenses and other current liabilities

3 Months Ended

Mar. 31, 2022

Payables and Accruals [Abstract]

Accrued expenses and other current liabilities

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


	As of March 31, 2022		As of December 31, 2021
Accrued manufacturing costs	$	30,806	$	15,722
Accrued goods and services	19,119		24,273
Accrued clinical and contract research organization costs	18,628		17,769
Accrued employee compensation	15,744		41,095
Accrued professional fees	1,674		1,665
Deferred revenue, current portion	1,822		2,282
Other	1,239		1,152
Total accrued expenses and other current liabilities	$	89,032	$	103,958

Accrued employee compensation as of December 31, 2021 includes severance costs associated with the Company's orderly wind down of its European operations. As of March 31, 2022, the Company did not have any significant accrued expenses related to these restructuring costs.

Commitments and contingencies	3 Months Ended
Commitments and contingencies	Mar. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Other funding commitments The Company is party to various agreements, principally relating to licensed technology, that require future payments relating to milestones that may be met in subsequent periods or royalties on future sales of specified products. The Company may be obligated to make future development, regulatory, and commercial milestone payments, and royalty payments on future sales of specified products associated with its collaboration and license agreements. Payments under these agreements generally become due and payable upon achievement of such milestones or sales. When the achievement of these milestones or sales have occurred, the corresponding amounts are recognized in the Company’s financial statements. Additionally, the Company is party to various contracts with contract research organizations and contract manufacturers that generally provide for termination on notice, with the exact amounts in the event of termination to be based on the timing of the termination and the terms of the agreement. As compared to the contractual obligations and commitments as disclosed in the Company's 2021 Annual Report on Form 10-K, the Company's future minimum purchase commitments as of the period ended March 31, 2022 decreased by $14.4 million. Based on the Company’s development plans as of March 31, 2022, the Company may be obligated to make future development, regulatory, and commercial milestone payments, and royalty payments on future sales of specified products associated with its collaboration and license agreements. Payments under these agreements generally become due and payable upon achievement of such milestones or sales. When the achievement of these milestones or sales have occurred, the corresponding amounts are recognized in the Company’s financial statements. While there are no material legal proceedings the Company is aware of, the Company may become party to various claims and complaints arising in the ordinary course of business, including securities class action litigation. The Company enters into standard indemnification agreements in the ordinary course of business. Pursuant to the 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. 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 generally unlimited. Management does not believe that any ultimate liability resulting from any of these claims will have a material adverse effect on its results of operations, financial position, or liquidity. However, management cannot give any assurance regarding the ultimate outcome of any claims, and their resolution could be material to operating results for any particular period. The Company also indemnifies each of its officers and directors for certain events or occurrences, subject to certain limits, while the officer or director is or was serving at the Company's request in such capacity, as permitted under Delaware law and in accordance with its certificate of incorporation and by-laws. The term of the indemnification period lasts as long as such officer or director may be subject to any proceeding arising out of acts or omissions of such officer or director in such capacity. The maximum amount of potential future indemnification is unlimited; however, the Company currently holds director and officer liability insurance. This insurance allows the transfer of risk associated with the Company's exposure and may enable it to recover a portion of any future amounts paid. The Company believes that the fair value of these indemnification obligations is minimal. Accordingly, it has not recognized any liabilities relating to these obligations.

Marketable securities

3 Months Ended

Mar. 31, 2022

Investments, Debt and Equity Securities [Abstract]

Marketable securities

The following table summarizes the marketable securities held at March 31, 2022 and December 31, 2021 (in thousands):


Description	Amortized cost / Cost		Unrealized gains		Unrealized losses		Fair value
March 31, 2022
U.S. government agency securities and treasuries	$	117,730	$	—	$	(2,025)	$	115,705
Corporate bonds	33,802		—		(135)		33,667
Commercial paper	9,823		—		—		9,823
Equity securities	4,305		—		(3,123)		1,182
Total	$	165,660	$	—	$	(5,283)	$	160,377
December 31, 2021
U.S. government agency securities and treasuries	$	128,902	$	—	$	(509)	$	128,393
Corporate bonds	49,366		—		(59)		49,307
Commercial paper	54,065		—		—		54,065
Equity securities	4,305		—		(614)		3,691
Total	$	236,638	$	—	$	(1,182)	$	235,456

No available-for-sale debt securities held as of March 31, 2022 or December 31, 2021 had remaining maturities greater than five years.

Stock-based compensation - Summary of Stock Option Activity Under Plan (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2022 $ / shares shares
Shares (in thousands)
Outstanding at beginning of period (in shares) \| shares	3,586
Granted (in shares) \| shares	890
Exercised (in shares) \| shares	(1)
Canceled or forfeited (in shares) \| shares	(735)
Outstanding at end of period (in shares) \| shares	3,740
Exercisable at end of period (in shares) \| shares	1,406
Vested and expected to vest at end of period (in shares) \| shares	3,740
Weighted- average exercise price per share
Outstanding at beginning of period (in dollars per share) \| $ / shares	$ 39.23
Granted (in dollars per share) \| $ / shares	7.79
Exercised (in dollars per share) \| $ / shares	1.04
Canceled or forfeited (in dollars per share) \| $ / shares	58.27
Outstanding at end of period (in dollars per share) \| $ / shares	29.14
Exercisable at end of period (in dollars per share) \| $ / shares	52.80
Vested and expected to vest at end of period (in dollars per share) \| $ / shares	$ 29.14

Fair value measurements (Tables)

3 Months Ended

Mar. 31, 2022

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 March 31, 2022 and December 31, 2021 (in thousands):


Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
March 31, 2022
Assets:
Cash and cash equivalents	$	106,260	$	106,260	$	—	$	—
Marketable securities:
U.S. government agency securities and treasuries	115,705		—		115,705		—
Corporate bonds	33,667		—		33,667		—
Commercial paper	9,823		—		9,823		—
Equity securities	1,182		1,182		—		—
Total	$	266,637	$	107,442	$	159,195	$	—
December 31, 2021
Assets:
Cash and cash equivalents	$	161,160	$	161,146	$	14	$	—
Marketable securities:
U.S. government agency securities and treasuries	128,393		—		128,393		—
Corporate bonds	49,308		—		49,308		—
Commercial paper	54,065		—		54,065		—
Equity securities	3,691		3,691		—		—
Total	$	396,617	$	164,837	$	231,780	$	—

Summary of Available-for-sale Debt Securities in Continuous Unrealized Loss Position


	Less than 12 months				12 months or greater				Total
Description	Fair value		Unrealized losses		Fair value		Unrealized losses		Fair value		Unrealized losses
March 31, 2022
U.S. government agency securities and treasuries	$	113,225	$	(2,005)	$	2,480	$	(20)	$	115,705	$	(2,025)
Corporate bonds	30,417		(135)		—		—		30,417		(135)
Total	$	143,642	$	(2,140)	$	2,480	$	(20)	$	146,122	$	(2,160)
December 31, 2021
U.S. government agency securities and treasuries	$	108,695	$	(505)	$	2,496	$	(4)	$	111,191	$	(509)
Corporate bonds	45,042		(56)		3,896		(2)		48,938		(58)
Total	$	153,737	$	(561)	$	6,392	$	(6)	$	160,129	$	(567)

Net loss per share

3 Months Ended

Mar. 31, 2022

Earnings Per Share [Abstract]

Net loss per share

Net loss per shareThe 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):


	For the three months ended March 31,
	2022	2021
Outstanding stock options (1)	5,645	6,458
Restricted stock units (1)	4,053	2,073
ESPP shares and other	264	884
	9,962	9,415

(1) Outstanding stock options and restricted stock units include awards outstanding to employees of 2seventy bio for shares of the Company's common stock.

Basis of presentation, principles of consolidation and significant accounting policies - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2022 segment
Accounting Policies [Abstract]
Number of operating segments	1

Commitments and contingencies - Narrative (Detail) $ in Millions	Mar. 31, 2022 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Decrease in purchase commitments	$ (14.4)

Basis of presentation, principles of consolidation and significant accounting policies	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Basis of presentation, principles of consolidation and significant accounting policies	Basis of presentation, principles of consolidation and significant accounting policies Basis of presentation 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”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States GAAP as included in the ASC and Accounting Standards Updates (“ASUs”) 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 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 March 31, 2022 and 2021. 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 condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements as of and for the year ended December 31, 2021, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2021, filed with the Securities and Exchange Commission (the “SEC”) on March 4, 2022 (the "2021 Annual Report on Form 10-K"). Certain items in the prior year’s condensed consolidated financial statements have been reclassified to conform to the current presentation. The Company has presented its oncology business together with its manufacturing facility in Durham, North Carolina as discontinued operations in its consolidated financial statements for the three months ended March 31, 2021 (see Note 3, Discontinued operations). The historical financial statements and footnotes have been recast accordingly. Amounts reported are computed based on thousands, except percentages, per share amounts or as otherwise noted. As a result, certain totals may not sum due to rounding. The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. 2seventy bio was a wholly-owned subsidiary until it became an independent publicly-traded company on November 4, 2021. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment. Discontinued operations The Company determined that the separation of its oncology business in November 2021 and the sale of its manufacturing facility in Durham, North Carolina in September 2021 represented multiple components of a single disposal plan that met the criteria for classification as a discontinued operation in accordance with ASC Subtopic 205-20, Discontinued Operations (“ASC 205-20”). Accordingly, the accompanying condensed consolidated financial statements for the three months ended March 31, 2021 have been updated to present the results of all discontinued operations reported as a separate component of loss in the consolidated statements of operations and comprehensive loss (see Note 3, Discontinued operations). Significant accounting policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three months ended March 31, 2022 are consistent with those discussed in Note 2 to the consolidated financial statements included in the Company’s 2021 Annual Report on Form 10-K, except as noted in the "Recent accounting pronouncements - Not yet adopted" section below. 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. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, and the measurement of right-of-use assets and lease liabilities, stock-based compensation expense, accrued expenses, income taxes, the assets and liabilities and losses related to discontinued operations and the assessment of the Company's ability to fund its operations for at least the next twelve months from the date of issuance of these financial statements. Recent accounting pronouncements Not yet adopted ASU No. 2022-02, Financial Instruments – Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures In March 2022, the FASB issued ASU 2022-02, Financial Instruments – Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures (“ASU 2022-02”), which eliminates the recognition and measurement guidance on troubled debt restructurings for creditors that have adopted ASC 326 and requires enhanced disclosure of loan modifications for borrowers experiencing financial difficulty. ASU 2022-02 amends the guidance on vintage disclosures to require disclosure of current-period gross write-offs by year of origination. The new standard will be effective beginning January 1, 2023. The adoption of ASU 2022-02 is not expected to have a material impact on the Company's financial position or results of operations.

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Revenue:
Total revenues	$ 1,945	$ 894
Operating expenses:
Research and development	77,875	82,843
Selling, general and administrative	36,106	63,569
Cost of product revenue	8,310	576
Total operating expenses	122,291	146,988
Loss from operations	(120,346)	(146,094)
Interest income, net	106	355
Other (expense) income, net	(1,912)	24,301
Loss before income taxes	(122,152)	(121,438)
Income tax (expense) benefit	0	(66)
Net loss from continuing operations	(122,152)	(121,504)
Net loss from discontinued operations	0	(84,304)
Net loss	$ (122,152)	$ (205,808)
Net loss per share from continuing operations - basic (in dollars per share)	$ (1.66)	$ (1.81)
Net loss per share from continuing operations - diluted (in dollars per share)	(1.66)	(1.81)
Net loss per share from discontinued operations - basic (in dollars per share)	0	(1.26)
Net loss per share from discontinued operations - diluted (in dollars per share)	0	(1.26)
Net loss per share - basic (in dollars per share)	(1.66)	(3.07)
Net loss per share - diluted (in dollars per share)	$ (1.66)	$ (3.07)
Weighted-average number of common shares used in computing net loss per share - basic (in shares)	73,688	66,976
Weighted-average number of common shares used in computing net loss per share - diluted (in shares)	73,688	66,976
Other comprehensive (loss) income:
Other comprehensive income (loss)	$ (1,548)	$ 56
Comprehensive loss	(123,700)	(205,752)
Product revenue
Revenue:
Revenue	1,408	724
Other revenue
Revenue:
Revenue	$ 537	$ 170

Basis of presentation, principles of consolidation and significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 2022
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation 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”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States GAAP as included in the ASC and Accounting Standards Updates (“ASUs”) 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 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 March 31, 2022 and 2021.
Consolidation	The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. 2seventy bio was a wholly-owned subsidiary until it became an independent publicly-traded company on November 4, 2021. All intercompany balances and transactions have been eliminated in consolidation. The Company views its operations and manages its business in one operating segment.
Discontinued operations	Discontinued operations The Company determined that the separation of its oncology business in November 2021 and the sale of its manufacturing facility in Durham, North Carolina in September 2021 represented multiple components of a single disposal plan that met the criteria for classification as a discontinued operation in accordance with ASC Subtopic 205-20, Discontinued Operations (“ASC 205-20”). Accordingly, the accompanying condensed consolidated financial statements for the three months ended March 31, 2021 have been updated to present the results of all discontinued operations reported as a separate component of loss in the consolidated statements of operations and comprehensive loss (see Note 3, Discontinued operations).
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. Actual results could materially differ from those estimates. Management considers many factors in selecting appropriate financial accounting policies and controls, and in developing the estimates and assumptions that are used in the preparation of these financial statements. Management must apply significant judgment in this process. In addition, other factors may affect estimates, including: expected business and operational changes, sensitivity and volatility associated with the assumptions used in developing estimates, and whether historical trends are expected to be representative of future trends. The estimation process often may yield a range of potentially reasonable estimates of the ultimate future outcomes and management must select an amount that falls within that range of reasonable estimates. This process may result in actual results differing materially from those estimated amounts used in the preparation of the financial statements. Estimates and judgments are used in the following areas, among others: future undiscounted cash flows and subsequent fair value estimates used to assess potential and measure any impairment of long-lived assets, including goodwill and intangible assets, and the measurement of right-of-use assets and lease liabilities, stock-based compensation expense, accrued expenses, income taxes, the assets and liabilities and losses related to discontinued operations and the assessment of the Company's ability to fund its operations for at least the next twelve months from the date of issuance of these financial statements.
Recent accounting pronouncements	Recent accounting pronouncements Not yet adopted ASU No. 2022-02, Financial Instruments – Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures In March 2022, the FASB issued ASU 2022-02, Financial Instruments – Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures (“ASU 2022-02”), which eliminates the recognition and measurement guidance on troubled debt restructurings for creditors that have adopted ASC 326 and requires enhanced disclosure of loan modifications for borrowers experiencing financial difficulty. ASU 2022-02 amends the guidance on vintage disclosures to require disclosure of current-period gross write-offs by year of origination. The new standard will be effective beginning January 1, 2023. The adoption of ASU 2022-02 is not expected to have a material impact on the Company's financial position or results of operations.

Discontinued operations - Significant Non-Cash Items and Capital Expenditures (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Operating activities:
Change in fair value of contingent consideration	$ 0	$ 369
Stock-based compensation expense	12,390	42,527
Investing activities:
Purchase of property, plant and equipment	(857)	(7,626)
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses	$ 2,134	2,238
Discontinued Operations, Disposed of by Means Other than Sale, Spinoff \| 2seventy bio
Operating activities:
Change in fair value of contingent consideration		369
Depreciation and amortization		3,800
Stock-based compensation expense		11,181
Investing activities:
Purchase of property, plant and equipment		(6,173)
Supplemental cash flow disclosures:
Purchases of property, plant and equipment included in accounts payable and accrued expenses		$ 1,954

Fair value measurements - Schedule of Unrealized Loss on Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair value
Less than 12 months	$ 143,642	$ 153,737
12 months or greater	2,480	6,392
Total	146,122	160,129
Unrealized losses
Less than 12 months	(2,140)	(561)
12 months or greater	(20)	(6)
Total	(2,160)	(567)
U.S. government agency securities and treasuries
Fair value
Less than 12 months	113,225	108,695
12 months or greater	2,480	2,496
Total	115,705	111,191
Unrealized losses
Less than 12 months	(2,005)	(505)
12 months or greater	(20)	(4)
Total	(2,025)	(509)
Corporate bonds
Fair value
Less than 12 months	30,417	45,042
12 months or greater	0	3,896
Total	30,417	48,938
Unrealized losses
Less than 12 months	(135)	(56)
12 months or greater	0	(2)
Total	$ (135)	$ (58)

Stock-based compensation - Narrative (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increased number of issuance of awards under the 2013 Plan (in shares)	2,800,000	2,700,000
Number of shares available for issuance (in shares)			4,100,000
Stock-based compensation expense			$ 12,390	$ 31,294
Stock option share exercised (in shares)			1,000
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option share exercised (in shares)			100,000
Proceed from option share exercised			$ 100
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			5,260	16,426
Unrecognized stock- based compensation expense			$ 97,500
Expected weighted-average period of recognition			2 years 2 months 12 days
ESPP shares and other
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 96	$ 4,651
Common shares reserved for future issuance (in shares)						200,000
Increase in shares authorized (in shares)					1,400,000
Shares of common stock issued under plan (in shares)			0
ESPP shares and other \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued under plan (in shares)				100,000

Property, plant and equipment, net - Summary of Property, Plant and Equipment Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 32,446	$ 30,112
Less accumulated depreciation and amortization	(21,212)	(20,406)
Property, plant and equipment, net	11,234	9,706
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	28,939	29,061
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	421	421
Office equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	117	117
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	12	12
Construction-in-progress
Property, Plant and Equipment [Line Items]
Total property, plant and equipment	$ 2,957	$ 501

Description of the business	3 Months Ended
Description of the business	Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the business	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 is a biotechnology company committed to researching, developing and commercializing potentially transformative gene therapies for severe genetic diseases. 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 selling, general and administrative support for these operations, including commercial-readiness activities. The Company’s programs in severe genetic diseases include betibeglogene autotemcel ("beti-cel", formerly "LentiGlobin for β-thalassemia gene therapy") as a treatment for β-thalassemia; lovotibeglogene autotemcel ("lovo-cel", formerly "LentiGlobin for SCD") as a treatment for sickle cell disease ("SCD"); and elivaldogene autotemcel ("eli-cel", formerly "Lenti-D gene therapy") as a treatment for cerebral adrenoleukodystrophy ("CALD"). In August 2021, the Company announced its intent to focus its severe genetic disease business on the U.S. market and further invest in research and development for its core programs in β-thalassemia, SCD, and CALD. As part of the strategy to focus on the U.S. market, it began executing an orderly wind down of its European operations, which will result in a reduction of selling, general and administrative costs and had an impact on the Company's excess inventory analysis, which is based on sales forecasts and projected inventory consumption levels. In November 2021, the Company completed the separation of its severe genetic disease and oncology programs into two separate, independent publicly traded companies, bluebird bio, Inc. and 2seventy bio, Inc. (“2seventy bio”), a Delaware corporation and wholly-owned subsidiary of the Company prior to the separation. bluebird retained its severe genetic disease programs, including programs for β-thalassemia, SCD, and CALD, with a focus on the U.S. market. In April 2022, the Board of Directors approved a comprehensive restructuring plan intended to reduce operating expenses and enhance the Company’s focus on achieving U.S. Food and Drug Administration ("FDA") approval for its programs in the U.S. The Company intends to maintain targeted research efforts focused on in-vivo lentiviral vector ("LVV") gene therapy and to deprioritize direct investments in reduced toxicity conditioning and cryopreserved apheresis. The restructuring is anticipated to produce up to $160 million in cost savings over the next two years. As part of the restructuring, bluebird plans to reduce its workforce by approximately 30% across the second and third quarters of 2022. Refer to Note 13, Subsequent events, for more information on this restructuring. As of March 31, 2022, the Company had cash, cash equivalents and marketable securities of approximately $266.6 million. The Company has incurred losses since inception and to date has financed its operations primarily through the sale of equity securities and, to a lesser extent, through collaboration agreements and grants from charitable foundations. As of March 31, 2022, the Company had an accumulated deficit of $3.84 billion. During the three months ended March 31, 2022, the Company incurred a loss of $122.2 million and used $125.3 million of cash in operations. The Company expects to continue to generate operating losses and negative operating cash flows for the next few years and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of beti-cel, eli-cel, and lovo-cel, and the achievement of a level of revenues adequate to support its cost structure. In accordance with Accounting Standards Codification 205-40, Going Concern ("ASC 205-40"), the Company evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about its ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. In performing its analysis, management excluded certain elements of its operating plan that cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from future equity or debt issuances, the release of restricted cash related to the Company’s 50 Binney Street lease, and the potential sale of priority review vouchers cannot be considered probable at this time because these plans are not entirely within the Company’s control nor have been approved by the Board of Directors as of the date of these condensed consolidated financial statements. The restructuring plan described above was approved by the Board of Directors in April 2022 and therefore was incorporated into the Company's assessment of its ability to continue as a going concern within one year after the date that these condensed consolidated financial statements are issued. The Company's expectation to generate operating losses and negative operating cash flows in the future and the need for additional funding to support its planned operations raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that these condensed consolidated financial statements are issued. Management's plans to alleviate the conditions that raise substantial doubt include implementing reduced 2022 spending, including projected savings through the move of the Company's headquarters to Assembly Row in Somerville, Massachusetts, the completion of its orderly wind down of European operations, the completion of its April 2022 restructuring plans, the potential sale of priority review vouchers that would be issued with the potential U.S. regulatory approvals of BLAs for beti-cel and/or eli-cel, and the pursuit of additional cash resources through public or private equity or debt financings. Management has concluded the likelihood that its plan to successfully obtain sufficient funding from one or more of these sources, or adequately reduce expenditures, while reasonably possible, is less than probable. In accordance with ASC 205-40, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least 12 months from the date of issuance of these condensed consolidated financial statements. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Condensed Consolidated Statements of Operations and Comprehensive Loss (unaudited) - (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Other comprehensive income (loss), tax	$ 0.0	$ 0.0

- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123586238&loc=d3e39076-109324

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 45
-Paragraph 20
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123586238&loc=d3e38679-109324

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=124431353&loc=SL124442407-227067

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(23))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(21))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32672-109319

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e640-108580

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(19))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

+ Details

Fair value measurements - Narrative (Detail) - USD ($)	1 Months Ended		3 Months Ended
Fair value measurements - Narrative (Detail) - USD ($)	Apr. 30, 2022	Jan. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on available-for-sale securities			$ 0	$ 0
Interest receivable			300,000		$ 300,000
Interest receivable, write-offs			0	0
Investment at fair value			1,182,000		$ 3,691,000
Proceeds from sale of equity securities		$ 31,300,000
Subsequent Event
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Realized gain (loss) on available-for-sale securities	$ 400,000
Debt securities	$ 29,700,000
Other (Expense) Income, Net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized gain (loss) on equity securities			$ 2,500,000	$ (28,400,000)

Description of the business - Narrative (Detail) - USD ($)	1 Months Ended	3 Months Ended
	Apr. 30, 2022	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Subsequent Event [Line Items]
Cash, cash equivalents and marketable securities		$ 266,600,000
Accumulated deficit		3,842,077,000		$ 3,719,925,000
Net loss		122,152,000	$ 205,808,000
Net cash used in operating activities		$ (125,296,000)	$ (203,327,000)
April 2022 Reduction \| Subsequent Event
Subsequent Event [Line Items]
Anticipated cost savings associated with restructuring	$ 160,000,000
Anticipated cost savings associated with restructuring, period of recognition	2 years
Plans to reduce workforce, as a percent	30.00%

Net loss per share (Tables)

3 Months Ended

Mar. 31, 2022

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):


	For the three months ended March 31,
	2022	2021
Outstanding stock options (1)	5,645	6,458
Restricted stock units (1)	4,053	2,073
ESPP shares and other	264	884
	9,962	9,415

(1) Outstanding stock options and restricted stock units include awards outstanding to employees of 2seventy bio for shares of the Company's common stock.