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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings
Net income	$ 15.5	$ 16.9	$ 24.0	$ 21.2
Shares
Weighted-average common shares outstanding (basic shares)	45.2	45.1	45.2	45.2
Adjustment for assumed dilution:
Weighted-average shares assuming dilution (diluted shares)	45.5	45.3	45.4	45.4
Earnings per share
Basic (in dollars per share)	$ 0.34	$ 0.38	$ 0.53	$ 0.47
Diluted (in dollars per share)	$ 0.34	$ 0.38	$ 0.53	$ 0.47
Restricted stock units
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.2	0.1	0.1	0.1
Performance shares
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.1	0.1	0.1