Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Provision for Income Taxes
Income tax expense (benefit)	$ 11.8	$ 6.2	$ 20.2	$ 16.1
Effective tax rates (as a percent)	27.30%	20.50%	25.50%	26.10%
Unrecognized tax benefits, excluding penalties and interest	$ 4.5		$ 4.5		$ 4.4
Accrued interest and penalties related to uncertain tax positions	0.4		0.4		$ 0.2
Penalties and interest (benefit) expense relating to unrecognized tax benefits	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Statutory tax rate (as a percent)			21.00%
Germany and Switzerland
Provision for Income Taxes
Increase in effective tax rate from impact of foreign statutory rates (as a percent)			4.00%
Germany | Foreign
Provision for Income Taxes
Foreign statutory tax rate for 2017 (as a percent)			30.00%
Switzerland | Foreign
Provision for Income Taxes
Foreign statutory tax rate for 2017 (as a percent)			20.00%