Property leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lessee, Lease, Description [Line Items]
Discount rate (in percent)	11.00%	4.00%
Weighted average remaining lease term	3 years 3 months 18 days	1 year 6 months
Operating lease expense	$ 0.7
Building
Lessee, Lease, Description [Line Items]
Right-of-use assets recognized with associated liability		$ 0.7
London | Building
Lessee, Lease, Description [Line Items]
Right-of-use assets recognized with associated liability	$ 2.7