Income Taxes - Narrative and Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance, January 1	$ 0.0	$ 1.5	$ 2.0
Decrease due to prior year tax positions	0.0	(1.5)	(0.5)
Ending Balance, December 31	0.0	$ 0.0	$ 1.5
Domestic Tax Authority
Income Taxes [Line Items]
Operating loss carryforwards	259.4
Deferred tax assets, net	54.5
State and Local Jurisdiction
Income Taxes [Line Items]
Operating loss carryforwards	262.7
Deferred tax assets, net	$ 14.2