Related-party transactions - Imputed Charges (Details) - Bluebird Bio $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 14,767
Imputed charge to bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	14,833
Imputed charge from bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(908)
Imputed charge to bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	1,891
Imputed charge from bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(1,130)
Imputed charge to bluebird bio for intangible assets
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	82
Other
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ (1)