Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Examination [Line Items]
Tax benefit from 2006-2009 IRS audit examination closure			$ 5.8
Additions for tax positions related to the current year			0.0	$ 4.6
Additions for tax positions of prior years			0.2	1.0
Unrecognized tax benefits including interest and penalties that would affect the Company's effective tax rate if recognized	$ 5.7	$ 15.6	5.7	15.6
Total accrued interest and penalties related to uncertain tax positions	3.7		3.7		$ 8.9
Increase (decrease) in income tax expense related to interest and penalties on unrecognized tax benefits	0.1	$ 0.6	5.2	1.5
Federal and state tax authorities
Income Tax Examination [Line Items]
Additions for tax positions related to the current year				$ 4.6
Settlement with taxing authority and lapse in statute of limitations
Income Tax Examination [Line Items]
Reasonably possible decrease in unrecognized federal and state tax benefits within twelve months	$ 1.8		$ 1.8