Significant agreements - Ionis Accounting analysis (Details) $ in Thousands	1 Months Ended		3 Months Ended
	Oct. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2023 USD ($) item	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Jul. 09, 2021 USD ($)	Dec. 31, 2020 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues			$ 4,896	$ 3,860
Deferred revenue		$ 71,340	$ 108,721		$ 61,873
Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of material rights associated with future payments | item			4
Total transaction price initially determined			$ 38,000			$ 38,000
Estimated amount payable to CROs						600
Collaboration revenues			2,784	$ 2,314
Deferred revenue		34,115	19,130		21,489
Ionis | Combined licenses and research and discovery performance obligation
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price initially determined			34,100
Ionis | Four material rights associated with credits for IND Acceptance fees
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price initially determined			$ 3,900
Ionis | Ionis Share Purchase Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price initially determined						$ 3,400
Ionis Evaluation and Option Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue					$ 21,500		$ 3,000
Amended Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues	$ 800	$ 800