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
	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share [Abstract]
Net income	$ 44.8	$ 39.2
Shares used in net income per common share - basic	65.0	64.7
Effect of dilutive shares	0.3	0.6
Shares used in net income per common share - diluted	65.3	65.3
Earnings per share:
Basic	$ 0.69	$ 0.61
Diluted	$ 0.69	$ 0.60