Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net income	$ 551.4	$ 350.1	$ 140.4
Denominator:
Shares used in net income per common share – basic	55.4	55.1	54.7
Effect of dilutive securities	0.3	0.2	0.4
Shares used in net income per common share – diluted	55.7	55.3	55.1
Net income per common share:
Basic	$ 9.95	$ 6.36	$ 2.57
Diluted	$ 9.90	$ 6.33	$ 2.55