Net Income per Share - Reconciliation of Basic to Diluted Net Income per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 26.3	$ 40.8	$ 71.1	$ 80.0
Shares used in net income per common share - basic	65.1	64.8	65.0	64.8
Effect of dilutive shares	0.2	0.6	0.3	0.6
Shares used in net income per common share - diluted	65.3	65.4	65.3	65.4
Earnings per share:
Basic	$ 0.40	$ 0.63	$ 1.09	$ 1.23
Diluted	$ 0.40	$ 0.62	$ 1.09	$ 1.22