Significant agreements - Ionis Accounting analysis (Details) $ in Thousands		1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 09, 2021 USD ($) item	Oct. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) item	Jun. 30, 2022 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2022 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues					$ 11,397	$ 4,378	$ 16,293	$ 8,238
Deferred revenue			$ 71,340		144,837		$ 144,837			$ 61,873
Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of material rights associated with future payments | item							4
Number of collaboration targets | item	4
Total transaction price initially determined	$ 38,000				38,000		$ 38,000
Upfront cash payment	31,000
Estimated amount payable to CROs	600
Period over which performance obligations will be performed							3 years
Material rights exercise period							4 years
Collaboration revenues					2,557	$ 2,255	$ 5,341	$ 4,569
Deferred revenue			34,115		17,713		17,713			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		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		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]
Upfront cash payment	$ 3,000			$ 3,000			3,000		$ 3,000
Deferred revenue									$ 3,000	$ 21,500
Amended Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment			1,600
Collaboration revenues		$ 800	$ 800
Third Amended Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues							$ 800