Commitments and contingencies - Novartis Option and License Agreement (Details) $ in Thousands			12 Months Ended
	Mar. 04, 2023 USD ($) item	Apr. 03, 2022 USD ($) item	Dec. 31, 2022 USD ($) item
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized | $			$ 269
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
Number of license options		3	2
Number of license options on additional targets		5
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
Revenue recognized | $			$ 54,000
Novartis Pharma, AG | Novartis License Agreement | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of license options		1
Novartis Pharma, AG | Forecast | Novartis License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of additional targets	2
Upfront payment | $	$ 54,000