Income Taxes - Income Tax Components (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
Components of income before taxes
United States									$ 38.9	$ 21.7	$ 23.5
Foreign									2.9	3.4	2.4
Earnings before income taxes	$ 15.2	$ 12.8	$ 12.3	$ 1.5	$ 3.8	$ 7.9	$ 10.2	$ 3.2	41.8	25.1	25.9
Current provision:
U.S. federal									13.9	11.5	9.5
Foreign									1.4	1.2	0.8
State									2.6	1.8	1.6
Total current									17.9	14.5	11.9
Deferred provision:
U.S. federal									(2.5)	(4.9)	(1.5)
Foreign									(0.4)	0.1	0.1
State									0.8	(4.9)	(10.7)
Total deferred									(2.1)	(9.7)	(12.1)
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)