Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income, basic EPS	$ 13.5	$ 15.1	$ 35.5	$ 33.8
Basic weighted-average shares (in shares)	46.3	46.2	46.3	46.2
Basic net income per common share (in dollars per share)	$ 0.29	$ 0.33	$ 0.77	$ 0.73
Effect of dilutive common share equivalents: [Abstract]
Net Income, diluted EPS	$ 13.5	$ 15.1	$ 35.5	$ 33.8
Diluted weighted-average shares (in shares)	46.5	46.6	46.5	46.6
Diluted net income per common share (in dollars per share)	$ 0.29	$ 0.33	$ 0.76	$ 0.73
Restricted Stock Units
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements	0.1	0.2	0.1	0.2
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ (0.01)	$ 0.00
Performance Shares
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements	0.1	0.2	0.1	0.2
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00