Commitments and contingencies - Novartis Option and License Agreement (Details) $ in Thousands		6 Months Ended
	Mar. 04, 2022 USD ($) item	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Revenue recognized | $		$ 1,214
Deferred revenue | $		10,881	$ 12,096
Novartis Pharma, AG | Novartis License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of transgenes	3
Number of additional targets	2
Upfront payment | $	$ 54,000
Additional fee agreed to pay | $	18,000
Aggregate maximum milestone payments to be received from collaborative partner | $	125,000
Aggregate milestone payments, if exercise rights | $	$ 12,500
Number of license options	3
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 options exercised	0
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 options exercised	1
Novartis Pharma, AG | Sales milestone | Novartis License Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate maximum milestone payments to be received from collaborative partner | $	$ 175,000