Japan pension plan (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Net periodic pension cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Japan
Defined Benefit Plan Disclosure [Line Items]
Pension liability	3.3		3.3		$ 3.7
Pension liability included in accrued and other current liabilities	$ 0.5		$ 0.5		$ 0.7