Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings
Net income	$ 8.5	$ 4.3
Shares
Weighted-average common shares outstanding (basic shares)	45.2	45.3
Adjustment for assumed dilution:
Weighted-average shares assuming dilution (diluted shares)	45.4	45.4
Earnings per share
Basic (in dollars per share)	$ 0.19	$ 0.09
Diluted (in dollars per share)	$ 0.19	$ 0.09
Restricted stock units
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.0
Performance shares
Adjustment for assumed dilution:
Incremental common shares attributable to share-based payment arrangements (in shares)	0.1	0.1