Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Contingency [Line Items]
Unrecognized tax benefit more likely than not percentage threshold	50.00%
Unrecognized tax benefits	$ 56.5
Unrecognized tax benefits that would impact effective tax rate	47.7
Interest expense or penalties, uncertain tax positions	0.3	$ 0.1
Accrued interest, uncertain tax positions	$ 1.7		$ 1.5
Federal statutory income tax rate	21.00%	35.00%
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Earliest year subject to examination	2000