Provision for Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Excess stock deductions excluded from deferred tax assets	$ 47.6
Increase in valuation allowance	$ 13.0
Income tax at U.S. statutory rate	34.00%	34.00%	34.00%
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 129.5	$ 94.5
State [Member]
Operating Loss Carryforwards [Line Items]
Tax credits	0.2	0.2
Alternative Minimum Tax Credit Carryforward [Member] | Federal [Member]
Operating Loss Carryforwards [Line Items]
Tax credits	$ 0.1	$ 0.1