Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 18.7	$ 13.5	$ 16.3	$ 5.7	$ 17.7	$ 15.1	$ 13.2	$ 5.5	$ 54.2	[1]	$ 51.5	[1]	$ 42.7	[1]
Weighted-average shares outstanding, basic EPS	46.2	46.3	46.3	46.4	46.4	46.2	46.2	46.4	46.3		46.2		46.2
Net income per common share, basic EPS (in dollars per share)	$ 0.41	$ 0.29	$ 0.35	$ 0.12	$ 0.39	$ 0.33	$ 0.29	$ 0.12	$ 1.17		$ 1.12		$ 0.93
Effect of dilutive common share equivalents: [Abstract]
Net income, diluted									$ 54.2		$ 51.5		$ 42.7
Weighted-average shares outstanding, diluted EPS	46.4	46.5	46.5	46.6	46.8	46.6	46.6	46.6	46.5		46.6		46.6
Net income per common share, diluted EPS (in dollars per share)	$ 0.41	$ 0.29	$ 0.35	$ 0.12	$ 0.38	$ 0.33	$ 0.29	$ 0.12	$ 1.17		$ 1.11		$ 0.92
Restricted stock units (RSUs)
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements									0.1		0.2		0.2
Net income per common share, share-based payment arrangements (in dollars per share)									$ 0.00		$ (0.01)		$ (0.01)
Stock options
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements									0.0		0.0		0.2
Net income per common share, share-based payment arrangements (in dollars per share)									$ 0.00		$ 0.00		$ 0.00
Performance shares
Effect of dilutive common share equivalents: [Abstract]
Incremental common shares attributable to share-based payment arrangements									0.1		0.2		0.0
Net income per common share, share-based payment arrangements (in dollars per share)									$ 0.00		$ 0.00		$ 0.00

[1] Amounts have been rounded for presentation purposes and might differ from unrounded results.