Income Taxes - Effective Income Tax Rate Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Federal income tax provision at the statutory rate									$ 23.2	$ 23.1	$ 19.4
State income taxes, net of federal benefit									2.3	2.5	2.3
Decrease in unrecognized tax benefits (inclusive of related interest and penalty)									(0.9)	(0.4)	(0.2)
Effect of foreign operations									(0.3)	(0.3)	(0.2)
Non-deductible acquisition costs									0	0	0.2
Tax credits and other, net									(0.6)	(0.5)	0
Total income tax provision	$ 7.9	$ 6.3	$ 7.9	$ 1.6	$ 8.2	$ 6.6	$ 8.1	$ 1.5	$ 23.7	$ 24.4	$ 21.5
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Federal income tax provision at the statutory rate									35.00%	35.00%	35.00%
State income taxes, net of federal benefit									3.50%	3.90%	4.20%
Decrease in unrecognized tax benefits (inclusive of related interest and penalty)									(1.40%)	(0.60%)	(0.40%)
Effect of foreign operations									(0.50%)	(0.50%)	(0.40%)
Non-deductible acquisition costs									0.00%	0.00%	0.40%
Tax credits and other, net									(0.90%)	(0.80%)	0.00%
Effective tax rate									35.70%	37.00%	38.80%