Derivatives and Financial Instruments - Recorded Amounts and Estimated Fair Values (Detail) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Total debt	$ 1,580.1	$ 1,638.7
Recorded Amount
Derivative [Line Items]
Variable rate debt	795.0	843.8
Fixed rate debt	800.0	819.3
Total debt	1,595.0	1,663.1
Fair Value
Derivative [Line Items]
Variable rate debt	795.0	843.8
Fixed rate debt	826.4	814.3
Total debt	$ 1,621.4	$ 1,658.1