Defined benefit and 401(k) savings plan - Swiss Plan Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Pension expense	$ 2.0	$ 2.4	$ 1.5
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of year	27.6	20.6
Employer contributions	1.4	1.4
Employee contributions	0.9	0.8
Net benefits received (paid)	0.5	6.8
Actual return on plan assets	(0.1)	0.3
Settlements	0.0	(4.5)
Currency impact	(1.0)	2.2
Fair value of plan assets, end of year	29.3	27.6	20.6
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, beginning of year	49.2	35.2
Service cost	2.4	1.9	1.3
Interest Cost	0.0	0.1	0.2
Employee contributions	0.9	0.8
Actuarial (gain) loss	(4.6)	5.0
Net benefits received (paid)	0.5	6.8
Settlements	0.0	(4.5)
Currency impact	(1.6)	3.9
Projected benefit obligation, end of year	46.8	49.2	$ 35.2
Funded status, end of year	(17.5)	(21.6)
Accumulated benefit obligation, end of year	$ 41.8	$ 43.0