Commitments and contingencies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Commitments and contingencies
Defined contribution	$ 0.1	$ 0.1	$ 0.2	$ 0.2
Product development and regulatory approval milestone payments	2.6		2.6
Commercial milestone payments	1.5		1.5
Collaborative agreement, milestone payments made	$ 0.0	$ 0.1	$ 0.0	$ 0.1