Income Taxes Income Taxes - Tax Cuts And Jobs Act Of 2017 Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Tax Credit Carryforward [Line Items]
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)	$ (6.5)
Tax cuts and jobs act of 2017, change in tax rate, deferred tax liability, income tax (expense) benefit	10.3
Tax cuts and jobs act of 2017, transition tax for accumulated foreign earnings, income tax expense (benefit)	3.8
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	(10.9)
Elimination of foreign earnings repatriated	0.0	$ (4.4)
Tax cuts and jobs act of 2017, measurement period adjustment, decrease in deferred tax assets (liabilities), net	8.1
Change in statutory tax rate, amount	(9.7)	$ 0.0	$ 0.0
Tax Cuts and Jobs Act of 2017, deferred income tax benefit	1.6
Tax cuts and jobs act of 2017, transition tax for accumulated foreign earnings	2.2
Retained Earnings
Tax Credit Carryforward [Line Items]
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	10.9
Federal Ministry of Finance, Germany
Tax Credit Carryforward [Line Items]
Elimination of foreign earnings repatriated				$ 4.1
Change in statutory tax rate, amount	$ 0.6