Benefit plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
United States | 401(k) Plan
Benefit plans
Contributions made	$ 0.3	$ 0.2	$ 0.2
Foreign Plan | U.K. Plan
Benefit plans
Contributions made	$ 0.7	$ 0.5	$ 0.3