Related-party transactions - Narrative (Details) $ in Thousands	2 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	Jun. 30, 2023	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Nov. 03, 2021 agreement
Related Party Transaction [Line Items]
Other income (expense)				$ (263,140)	$ (313,948)	$ (138,170)
Total operating expenses				354,636	368,470	386,292
Number of transition services agreements | agreement							2
Initial term of transition services agreement							2 years
Other income, net				6,055	21,647	18,056
Accrued expenses and other current liabilities	$ 55,410	$ 55,410		54,678	55,410
Accounts payable	6,024	$ 6,024		7,208	6,024
Bluebird Bio | Separation Agreement
Related Party Transaction [Line Items]
Other income (expense)	(200)			2,800
Total operating expenses	$ 1,800			200
Bluebird Bio | Transition Services Agreement
Related Party Transaction [Line Items]
Other income, net				10,000	1,400
Operating expenses				1,000	700
Area of sublease, as a percent		30.00%
Sublease income				4,900	800
Amount due to related party				100
Amount due from related party				$ 1,900
Bluebird Bio | Transition Services Agreement | Forecast
Related Party Transaction [Line Items]
Area of sublease, as a percent			23.00%
Bluebird Bio | Management Costs and Corporate Support Services
Related Party Transaction [Line Items]
Allocations for management costs and corporate support services provided to the Company					$ 55,300	$ 76,600