Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal income tax provision at the statutory rate	$ 7.7	$ 7.1	$ 11.9	$ 19.5
State income taxes, net of federal benefit	0.8	0.7	1.3	1.9
Decrease in unrecognized tax benefits (inclusive of related interest and penalty)	(0.3)	(0.4)	(0.3)	(0.4)
Excess tax benefits from stock-based award payments	0.0	0.0	(1.5)	0.0
Tax credits and other, net	(0.1)	(0.7)	(0.2)	(0.7)
Income tax provision	$ 8.1	$ 6.7	$ 11.2	$ 20.3
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal income tax provision at the statutory rate	35.00%	35.00%	35.00%	35.00%
State income taxes, net of federal benefit	3.90%	3.40%	3.80%	3.30%
Decrease in unrecognized tax benefits (inclusive of related interest and penalty)	(1.30%)	(1.80%)	(0.80%)	(0.70%)
Excess tax benefits from stock-based award payments	(0.00%)	(0.00%)	(4.50%)	(0.00%)
Tax credits and other, net	(0.40%)	(3.40%)	(0.50%)	(1.20%)
Income tax provision	37.20%	33.20%	33.00%	36.40%