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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement revenue	$ 14,831	$ 2,422	$ 18,020	$ 114,398
Research and development expense	(131,427)	(140,431)	(429,614)	(450,862)
Revenue catch-up adjustment	22,677	19,273	42,943	240,026
Bristol-Myers Squibb | U.S. | Ide Cel Research And Development Services | License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense	(5,660)	(16,084)	(31,678)	(21,164)
Bristol-Myers Squibb | U.S. | Ide Cel Revenue Services | License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaborative arrangement revenue	0	0	0	108,196
Revenue catch-up adjustment		169,200
Bristol-Myers Squibb | Outside of U.S. | Ide Cel License And Manufacturing Services | License and Manufacturing Services
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue	$ 5,314	6,913	$ 14,698	$ 94,733
Revenue catch-up adjustment		$ 169,200