Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Provision for Income Taxes
Income tax provision	$ 9.8	$ (4.0)	$ 25.9	$ 3.8
Effective tax rates (as a percent)	20.70%	(9.30%)	23.70%	4.30%
Unrecognized tax benefits, excluding penalties and interest	$ 6.1		$ 6.1			$ 6.2
Portion of unrecognized tax benefits, which if recognized, would result in a reduction of the effective tax rate	5.2		5.2			5.3
Accrued interest and penalties related to uncertain tax positions	0.5		0.5			$ 0.5
Penalties and interest expense relating to unrecognized tax benefits	$ 0.0	$ 0.9	$ 0.0	$ 1.5
Expected
Provision for Income Taxes
US statutory rate (as a percent)					35.00%
Expected | Germany and Switzerland
Provision for Income Taxes
Reduction in effective tax rate from impact of foreign statutory rates (as a percent)					8.80%
Expected | Germany | Foreign
Provision for Income Taxes
Foreign statutory tax rate for 2017 (as a percent)					28.00%
Expected | Switzerland | Foreign
Provision for Income Taxes
Foreign statutory tax rate for 2017 (as a percent)					20.50%