The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 730
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482916/730-10-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 912
-SubTopic 730
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482517/912-730-25-1

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481283/985-20-50-1

Name:	us-gaap_ResearchAndDevelopmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Collaborative arrangements and strategic partnerships - Summary of Amounts Associated with Research and Development Services (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]
Net R&D Expenses													$ (230,758)	$ (248,735)	$ (252,617)
Ide-cel research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Net R&D Expenses	$ (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)
Bristol-Myers Squibb \| Ide-cel research and development services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Obligation for share of research and development expenses	(7,237)	(6,980)	(7,195)	(9,461)	(8,197)	(10,672)	(7,418)	(8,118)	(8,780)	(9,398)	(11,559)	(22,110)	(30,873)	(34,405)	(51,847)
Reimbursement of research and development expenses	$ 151	$ 860	$ 1,543	$ 4,590	$ 1,960	$ 1,420	$ 1,955	$ 1,225	$ 945	$ 3,738	$ 2,366	$ 4,752	$ 7,144	$ 6,560	$ 11,801