Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Numerator
Net Income	$ 232.0	$ 189.1
Denominator
Weighted Average Common Shares - Basic	164,073,900	178,291,500
Dilution for Assumed Exercises of Nonvested Stock Awards	325,600	590,900
Weighted Average Common Shares - Assuming Dilution	164,399,500	178,882,400
Net Income Per Common Share
Basic	$ 1.41	$ 1.06
Assuming Dilution	$ 1.41	$ 1.06