Commitments and contingencies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Commitments and contingencies
Defined contribution	$ 0.1	$ 0.1	$ 0.1	$ 0.1
Product development and regulatory approval milestone payments	2.6		2.6
Commercial milestone payments	1.5		1.5
Collaborative agreement, milestone payments made	$ 0.1	$ 0.0	$ 0.1	$ 0.0