Collaborative arrangements and strategic partnerships - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended				9 Months Ended
	Jan. 31, 2023 USD ($) $ / shares shares	Aug. 31, 2018 USD ($) target accounting_unit $ / shares shares	Sep. 30, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Apr. 30, 2023 USD ($)	Oct. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) performance_obligation
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
One time restructuring expenses			$ 300	$ 5,400
Proceeds from issuance of common stock to Regeneron, net of issuance costs							$ 0	$ 9,859
Common stock, $0.0001 par value; 200,000 shares authorized, 51,512 and 50,632 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively			5				$ 5		$ 5
Number of accounting units | accounting_unit		2
Bristol-Myers Squibb | Abecma Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Agreement termination notice period							90 days
Regeneron | Collaboration Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue balance recognized as gross revenues						$ 5,300	$ 4,700	16,200
Regeneron | Research and Development Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Purchase price premium		$ 37,000					1,100
Collaborative arrangement amortization period		5 years
Collaboration agreement, transaction price		$ 100,000
Collaborative arrangement amount attributed to joint research activities		45,500
Collaborative arrangement amount attributed to joint research activities, net funding advancement		8,500
Regeneron | Research and Development Services | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement amount attributed to equity sold		$ 54,500
Regeneron | Regeneron Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of initial collaboration targets | target		6
Research collaboration term		5 years
Regeneron | Regeneron Collaboration Agreement | Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable		$ 130,000
Regeneron | Regeneron Collaboration Agreement, Amendment One
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage	50.00%
Contract with customer liability			7,800				7,800
Regeneron | Regeneron Collaboration Agreement, Amendment One | Pre-Clinical Costs To Study Combinations
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage	75.00%
Regeneron | Regeneron Collaboration Agreement, Amendment One | Clinical Study Costs Involving Regeneron Agents
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage	100.00%
Regeneron | Regeneron Collaboration Agreement, Amendment One | MUC-16 Development Candidate Nomination
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 2,000
Regeneron | Regeneron Collaboration Agreement, Amendment One | MUC-16 IND Acceptance
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	3,000
Regeneron | Regeneron Collaboration Agreement, Amendment One | Last Patient Dosed Or Dosing Of The 10th Patient
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	5,000
Regeneron | Regeneron Collaboration Agreement, Amendment One | MUC-16 Development Candidate Nomination After Achievement Of IND Acceptance
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	1,000
Regeneron | Regeneron Collaboration Agreement, Amendment One | MUC-16
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable	$ 4,000
Revenue					$ 4,000
Regeneron | Share Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares issued (in shares) | shares	1,114,827	100,000
Common stock price per share (in dollars per share) | $ / shares	$ 17.94
Proceeds from issuance of common stock to Regeneron, net of issuance costs	$ 20,000
Common stock, $0.0001 par value; 200,000 shares authorized, 51,512 and 50,632 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively	9,900
Contract with customer liability	$ 10,100
Regeneron | Share Purchase Agreement | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement research initial funding obligation, percentage		50.00%
Common stock price per share (in dollars per share) | $ / shares		$ 238.10
Proceeds from issuance of common stock to Regeneron, net of issuance costs		$ 100,000
Purchase price premium		$ 37,000
Regeneron | Share Purchase Agreement | Common stock | Bluebird Bio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Common stock shares issued (in shares) | shares		400,000
Proceeds from issuance of common stock to Regeneron, net of issuance costs		$ 63,000
Regeneron | Regeneron Collaboration Agreement, Original And Amendment Combined
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability			11,200				11,200
JW Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability											$ 3,000
Estimated variable consideration											7,300
Estimated variable consideration reimbursement											$ 4,300
Novo Nordisk A/S | Novo Collaboration and License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability												$ 5,000
Revenue			0			$ 1,100	3,500	$ 4,700
Estimated variable consideration												$ 11,700
Number of performance obligations | performance_obligation												2
Estimated variable consideration, upfront payment												$ 5,000
Estimated variable consideration, research reimbursement												6,700
Novo Nordisk A/S | Novo Collaboration and License Agreement | Scientific Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable										$ 15,000		15,000
Novo Nordisk A/S | Novo Collaboration and License Agreement | Extension of Research Plan without Achieving Scientific Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable												9,000
Novo Nordisk A/S | Novo Collaboration and License Agreement | License and Manufacturing Services
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable												26,000
Novo Nordisk A/S | Novo Collaboration and License Agreement | Development and Commercialization Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable												$ 72,000
Novo Nordisk A/S | Novo Collaboration and License Agreement | Milestone Achievement, Option To In-License Technology From Third Party
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payments receivable										9,000
Contract with customer liability										$ 6,000
Novo Nordisk A/S | Novo Collaboration and License Agreement | Milestone Achievement, Option To In-License Technology From Third Party And Upfront Payment
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contract with customer liability			$ 11,000				$ 11,000