Basic and Diluted Earnings (Loss) Per Common Share - Components of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Numerator:
Income from continuing operations, net of taxes	$ 26.0	$ 14.4	$ 25.2	$ 23.1
(Loss) income from discontinued operations, net of taxes	0.0	3.7	(0.1)	0.5
Net income	$ 26.0	$ 18.1	$ 25.1	$ 23.6
Denominator:
Weighted average common shares outstanding - Basic (shares)	52,440,580	52,356,798	52,413,552	52,356,798
Effect of dilutive restricted stock (shares)	169,225	29,583	174,316	20,416
Weighted average common shares outstanding - Diluted (shares)	52,609,805	52,386,381	52,587,868	52,377,214
Basic earnings per common share:
Continuing operations (usd per share)	$ 0.50	$ 0.27	$ 0.48	$ 0.44
Discontinued operations (usd per share)	0.00	0.07	0.00	0.01
Net income (usd per share)	0.50	0.34	0.48	0.45
Diluted earnings per common share:
Continuing operations (usd per share)	0.49	0.27	0.48	0.44
Discontinued operations (usd per share)	0.00	0.07	0.00	0.01
Net income (usd per share)	$ 0.49	$ 0.34	$ 0.48	$ 0.45