Income Taxes - Accounting change (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2017
Federal
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross operating loss carryforwards		$ 473.6
State
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross operating loss carryforwards		$ 304.0
ASU 2016-09 | Federal | ASU Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross operating loss carryforwards	$ 27.0
Tax affect	9.2
Valuation allowance	9.2
ASU 2016-09 | State | ASU Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Gross operating loss carryforwards	23.3
Tax affect	1.2
Valuation allowance	$ 1.2