Significant agreements - Ionis (Details)		1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 09, 2021 USD ($) item	Dec. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) item	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration revenues				$ 4,378,000	$ 1,785,000	$ 8,238,000	$ 3,593,000
Deferred revenue		$ 71,340,000		66,379,000		$ 66,379,000		$ 35,156,000
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	$ 38,000,000.0			38,000,000		$ 38,000,000
Upfront cash payment	31,000,000.0
Estimated amount payable to CROs	600,000
Expected period for satisfaction of performance obligations						3 years
Material rights exercise period						4 years
Collaboration revenues				2,255,000	$ 0	$ 4,569,000	$ 0
Deferred revenue		34,115,000		26,387,000		26,387,000
Ionis | Combined licenses and research and discovery performance obligation
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price initially determined				34,100,000		34,100,000
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				$ 3,900,000		3,900,000
Ionis | Ionis Share Purchase Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total transaction price initially determined	3,400,000
Ionis Evaluation and Option Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment	$ 3,000,000.0		$ 3,000,000.0			$ 3,000,000.0		3,000,000.0
Deferred revenue		34,115,000						$ 3,000,000
Amended Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment		1,600,000
Collaboration revenues		800,000
Amended Ionis | Service for initial six month
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment		800,000
Amended Ionis | Service for additional six month
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment		$ 800,000