Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income, basic EPS	$ 13.2	$ 12.0	$ 18.7	$ 14.4
Weighted-Average Shares Outstanding, basic EPS	23.1	23.1	23.1	23.1
Net Income Per Common Share, basic EPS (in dollars per share)	$ 0.57	$ 0.52	$ 0.81	$ 0.63
Effect of dilutive common share equivalents: [Abstract]
Net Income, diluted EPS	$ 13.2	$ 12.0	$ 18.7	$ 14.4
Weighted-Average Shares Outstanding, diluted EPS	23.3	23.2	23.3	23.2
Net Income Per Common Share, diluted EPS (in dollars per share)	$ 0.57	$ 0.52	$ 0.81	$ 0.62
Restricted Stock Units
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements	0.1	0.0	0.1	0.1
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ (0.01)
Stock options
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements	0.0	0.1
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00
Performance Shares
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements	0.1	0.0	0.1	0.0
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00