Commitments and contingencies - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commitments and contingencies
Operating lease cost	$ 5,408	$ 3,790	$ 1,224
Variable lease cost	2,777	1,643	612
Total lease cost	$ 8,185	$ 5,433	$ 1,836
Weighted-average remaining operating lease term (years)	2 years 10 months 24 days	4 years 2 months 12 days
Weighted-average discount rate	7.90%	7.00%