Collaborative arrangements and strategic partnerships - Summary of Revenue Recognized or Expense Incurred for Joint Ide-cel Development Efforts Related to Combined Unit of Accounting for its License and Vector Manufacturing of Ide-cel (Detail) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense													$ (230,758)	$ (248,735)	$ (252,617)
Ide-cel research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense	$ (7,086)	$ (6,120)	$ (5,652)	$ (4,871)	$ (6,237)	$ (9,252)	$ (5,463)	$ (6,893)	$ (7,835)	$ (5,660)	$ (9,193)	$ (17,358)	(23,729)	(27,845)	(40,046)
U.S. | Ide Cel revenue services | License and manufacturing services | Accounting Standards Update 2014-09 | Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue													0	0	533
U.S. | Ide-cel research and development services | License and manufacturing services | Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development expense													0	0	0
Outside of U.S. | Ide-cel license and manufacturing services | License and manufacturing services | Bristol-Myers Squibb
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue													$ 14,751	$ 13,226	$ 16,895