Significant agreements - Ionis Collaboration Agreement (Details) $ in Millions		1 Months Ended					6 Months Ended	12 Months Ended
	Jul. 09, 2021 USD ($) item	Apr. 30, 2023 USD ($)	Oct. 31, 2022 USD ($)	Aug. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jun. 30, 2023 USD ($)	Dec. 31, 2020 USD ($)
Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Period for which research and discovery activities will be performed with no additional consideration	3 years
Upfront cash payment	$ 31.0
Number of payments of a mid-single-digit million dollar, failing to achieve the specified development diligence | item	3
Number of collaboration targets | item	4
Number of years over which royalty is payable	10 years
Ionis Evaluation and Option Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment	$ 3.0					$ 3.0	$ 3.0	$ 3.0
Amended Ionis
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment					$ 1.6
Amended Ionis | Service for initial six month
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment				$ 0.8
Amended Ionis | Service for additional six month
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment			$ 0.8
Third Ionis Amendment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment		$ 0.8
Third Ionis Amendment | Additional research service for a year
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment		$ 0.8