Basic and Diluted (Loss) Earnings Per Common Share - Components of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Income from continuing operations, net of taxes	$ 24.4	$ 10.7	$ 17.5	$ 19.2
Income from discontinued operations, net of taxes	0.3	0.4	0.3	0.4
Net income	$ 24.7	$ 11.1	$ 17.8	$ 19.6
Denominator:
Weighted average common shares outstanding - Basic (shares)	52,356,798	52,349,583	52,356,798	52,340,463
Effect of dilutive restricted stock (shares)	0	7,580	0	16,541
Weighted average common shares outstanding - Diluted (shares)	52,356,798	52,357,163	52,356,798	52,357,004
Income from Continuing Operations, Per Basic Share	$ 0.46	$ 0.20	$ 0.33	$ 0.36
Income from Discontinued Operations, Net of Tax, Per Basic Share	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Basic earnings per share (usd per share)	$ 0.47	$ 0.21	$ 0.34	$ 0.37
Income from Continuing Operations, Per Diluted Share	$ 0.46	$ 0.20	$ 0.33	$ 0.36
Income from Discontinued Operations, Net of Tax, Per Diluted Share	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Diluted earnings per share (usd per share)	$ 0.47	$ 0.21	$ 0.34	$ 0.37