Commitments and contingencies - Novartis Option and License Agreement (Details) $ in Thousands			1 Months Ended		3 Months Ended
	Mar. 01, 2023 USD ($) item	Mar. 04, 2022 USD ($) item	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) item	Mar. 31, 2023 USD ($)	Mar. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenue | $					$ 150,480	$ 658
Related party collaboration receivable | $			$ 328	$ 257	328
Novartis Pharma, AG | Novartis License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgenes		3
Number of additional targets	2	2
Upfront payment | $	$ 54,000	$ 54,000	25,000
Additional fee agreed to pay | $	$ 18,000
Number of royalties	2
Exercise payment | $	$ 25,000
Number of targets not elected to license a capsid	1
Aggregate milestone payments, if exercise rights | $	$ 12,500
Number of license options				2
Number of license option exercise for each target		1
Number of Alliance Managers		2
Number of options		1
Number of major market countries received regulatory approval		3
Number of days written notice required by reporting entity to terminate agreement	90 days
Number of performance obligations		3
Number of material rights		3
Allocation of transaction price | $		$ 18,000
Novartis Pharma, AG | Novartis License Agreement | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of license options		3
Novartis Pharma, AG | Novartis License Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of license options		5
Novartis Pharma, AG | Option and license agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Exercise payment | $					25,000
Revenue recognized | $					79,000
Collaboration revenue | $					79,000
Related party collaboration receivable | $			$ 25,000		$ 25,000
Novartis Pharma, AG | First Material Right
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront payment | $				$ 54,000