Discontinued operations - Revenue and Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net loss	$ 0	$ (63,982)	$ 0	$ (234,015)
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		21,659		40,888
Research and development		57,748		189,053
Selling, general and administrative		26,048		72,945
Share of collaboration loss		0		10,071
Change in fair value of contingent consideration		48		464
Total operating expenses		84,164		274,644
Loss from operations		(62,505)		(233,756)
Interest income, net		159		735
Other income, net		(1,636)		(994)
Loss before income taxes		(63,982)		(234,015)
Income tax benefit (expense)		0		0
Net loss		(63,982)		(234,015)
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		6,312		17,544
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		14,738		17,927
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		609		5,417
Cost of royalty and other revenue		$ 320		$ 2,111