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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings
Net income	$ 16.9	$ 17.7	$ 21.2	$ 19.0
Shares
Weighted-average common shares outstanding (basic shares)	45.1	45.9	45.2	45.9
Adjustment for assumed dilution:
Weighted-average shares assuming dilution (diluted shares)	45.3	46.1	45.4	46.1
Earnings per share
Basic (in dollars per share)	$ 0.38	$ 0.39	$ 0.47	$ 0.41
Diluted (in dollars per share)	$ 0.38	$ 0.38	$ 0.47	$ 0.41
Restricted stock units
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.2	0.1	0.2
Performance shares
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.0	0.1	0.0