Significant agreements - Ionis Evaluation and Option Agreement (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Jul. 09, 2021	Jan. 31, 2021	Dec. 31, 2020	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Deferred revenue				$ 114,547	$ 135,194	$ 61,873
Ionis Evaluation and Option Agreement
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Upfront cash payment	$ 3,000	$ 3,000	$ 3,000
Deferred revenue			$ 3,000		$ 12,500