Related Party Disclosures - Imputed Charges (Details) - Bluebird Bio - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 4,813	$ 13,274
Imputed charge to bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	4,519	13,440
Imputed charge from bluebird bio for leases
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(209)	(836)
Imputed charge to bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	507	1,714
Imputed charge from bluebird bio for property, plant and equipment
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	(13)	(1,125)
Imputed charge to bluebird bio for intangible assets
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	9	82
Other
Related Party Transaction [Line Items]
Related party transaction, amounts of transaction	$ 0	$ (1)