Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Undistributed earnings of foreign subsidiaries on which U.S. income taxes are not provided	$ 740.0
Unrecognized deferred withholding taxes on undistributed earnings of foreign subsidiaries	27.0
Gross unrecognized tax benefits, excluding interest	4.4
Reasonably possible reduction in unrecognized tax benefits due to statutes of limitations expiring and favorably settling with taxing authorities	0.8
Reconciliation of beginning and ending amount of unrecognized tax benefits
Gross unrecognized tax benefits at the beginning of the year	6.2	$ 33.2	$ 40.0
Gross decreases - tax positions in prior periods		(4.8)	(1.5)
Gross increases - current period tax positions		0.9	0.4
Settlements		(21.3)	(2.7)
Lapse of statutes	(1.8)	(1.8)	(3.0)
Gross unrecognized tax benefits at the end of the year	4.4	6.2	$ 33.2
Accrued interest and penalties related to uncertain tax positions	0.2	0.5
Penalties and interest (benefit) expense relating to unrecognized tax benefits	$ (0.3)	$ (1.8)
Statutory tax rate (as a percent)	35.00%	35.00%	35.00%
Change in tax rates (as a percent)	0.90%	0.20%	1.30%
Germany and Switzerland
Reconciliation of beginning and ending amount of unrecognized tax benefits
Change in tax rates (as a percent)	7.80%
Germany
Reconciliation of beginning and ending amount of unrecognized tax benefits
Statutory tax rate (as a percent)	30.00%
Switzerland
Reconciliation of beginning and ending amount of unrecognized tax benefits
Statutory tax rate (as a percent)	20.00%