Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Tax Contingency [Line Items]
Income tax expense (benefit)	$ 4.7		$ 0.0	$ 70.9	$ 3.3
Valuation allowance	4.9
State income tax benefit	2.5
Deferred income tax expense	$ 14.0		$ 0.4	79.8	$ 3.6
Effective income tax rate (as a percent)			0.00%		19.50%
Federal statutory tax rate (as a percent)			35.00%		35.00%
IRS
Income Tax Contingency [Line Items]
Deferred income tax expense		$ 148.6
Deferred tax liability		$ 84.4
Net impact on deferred tax expense				$ 64.2