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		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Earnings Per Share [Abstract]
Net income	$ 33.6	$ 35.4	$ 104.7	$ 115.4
Shares used in net income per common share - basic	65.1	64.9	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	65.5	65.3	65.4
Earnings per share:
Basic	$ 0.52	$ 0.55	$ 1.61	$ 1.78
Diluted	$ 0.51	$ 0.54	$ 1.60	$ 1.76