Income Taxes - Effective Tax Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of income tax provision (benefit) to the amount computed by multiplying book income/(loss) before income taxes by federal income tax rate
Tax at statutory rate									$ 14.6	$ 8.8	$ 9.1
Permanent differences									0.8	1.4	1.0
State taxes, net of federal benefit									1.3	0.3	0.8
Effect of foreign tax rates									0.0	(0.1)	0.0
Minority interest									(1.0)	(1.0)	(1.1)
Equity investments in unconsolidated entities									0.0	0.0	2.4
Current year adjustment to deferred taxes									1.3	1.5	(1.3)
Recognition of tax credits									(1.4)	(1.2)	(1.5)
Other									0.4	0.6	(0.5)
Income tax expense before change in valuation allowance									16.0	10.3	8.9
Change in valuation allowance									(0.2)	(5.5)	(9.1)
Income tax (benefit) expense	$ 4.9	$ 5.1	$ 4.9	$ 0.9	$ 0.4	$ 3.5	$ (0.4)	$ 1.3	$ 15.8	$ 4.8	$ (0.2)