Summary of significant accounting policies - Government grants (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Summary of significant accounting policies
Reduction of research and development related to government grant arrangements	$ 1.5	$ 3.0	$ 0.7
Government grant funding remaining for future cost reimbursement	$ 1.1