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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income, basic EPS	$ 13.7	$ 13.5	$ 22.7	$ 35.5
Weighted-average shares outstanding, basic EPS (in shares)	46.3	46.3	46.3	46.3
Net income per common share, basic EPS (in dollars per share)	$ 0.29	$ 0.29	$ 0.49	$ 0.77
Effect of dilutive common share equivalents:
Net income, diluted EPS	$ 13.7	$ 13.5	$ 22.7	$ 35.5
Weighted-average shares outstanding, diluted EPS (in shares)	46.4	46.5	46.4	46.5
Diluted earnings per share (in dollars per share)	$ 0.29	$ 0.29	$ 0.49	$ 0.76
Restricted Stock Units
Effect of dilutive common share equivalents:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.0	0.1	0.0	0.1
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ (0.01)
Performance Shares
Effect of dilutive common share equivalents:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.1	0.1	0.1
Net income per common share, share-based payment arrangements (in dollars per share)	$ 0.00	$ 0.00	$ 0.00	$ 0.00