Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Amortization of pension and postretirement items:
Tax benefit	$ (7,600)	$ (6,800)	$ (35,000)	$ (30,200)
Derivative, Gain (Loss) on Derivative, Net	0	200	1,000	1,600
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan			76,300	56,800
Interest Rate Swap [Member] | Derivatives designated as hedging instrument [Member] | Interest Expense [Member]
Amortization of pension and postretirement items:
Derivative, Gain (Loss) on Derivative, Net	$ 100	$ 300	$ 300	$ 600