Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Numerator
Net Income (Loss)	$ (419.7)	$ 39.7	$ 69.2	$ 564.4
Denominator
Weighted Average Common Shares - Basic	158,607,300	170,248,100	159,355,600	174,152,500
Dilution for Assumed Exercises of Stock Options and Nonvested Stock Awards	0	340,700	379,600	417,500
Weighted Average Common Shares - Assuming Dilution	158,607,300	170,588,800	159,735,200	174,570,000
Net Income Per Common Share
Basic	$ (2.65)	$ 0.23	$ 0.43	$ 3.24
Assuming Dilution	$ (2.65)	$ 0.23	$ 0.43	$ 3.23