Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ / shares in Units, shares in Millions	1 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended
	Oct. 31, 2021	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 2,439,000		$ (2,865,000)		$ (2,865,000)	$ (2,865,000)	$ (6,267,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						8,176,000	3,617,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax						(2,872,000)	(979,000)
Net current-period other comprehensive income (loss)		$ 1,881,000		$ 833,000		5,304,000	2,638,000
Ending balance		2,439,000		(3,629,000)		$ 2,439,000	(3,629,000)
Stock Issued During Period, Shares, Dividend Reinvestment Plan	0.1		0.3			0.1
Stock Issued During Period, Value, Dividend Reinvestment Plan	$ 127.40		$ 86.12			$ 116.63
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan	$ 1,800,000		$ 22,000,000			$ 6,600,000
Common Stock Shares Issued At The Market								0.7
Shares Issued Price Per Share - At The Market								$ 82.93
Proceeds From Issuance Of Common Stock - At The Market					61,000,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan	0.1		0.3			0.1
Stock Issued During Period, Value, Dividend Reinvestment Plan	$ 127.40		$ 86.12			$ 116.63
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan	1,800,000		22,000,000			6,600,000
Fees on Equity Issuance - At The Market					1,500,000
Maximum [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Proceeds from Stock Plans			75,000,000
Proceeds from Stock Plans			75,000,000
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4,954,000)		(5,146,000)		(5,146,000)	(5,146,000)	(4,933,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax						192,000	198,000
Net current-period other comprehensive income (loss)						192,000	198,000
Ending balance		(4,954,000)		(4,735,000)		(4,954,000)	(4,735,000)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	7,403,000		2,309,000		2,309,000	2,309,000	(1,334,000)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						8,121,000	3,594,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax						(3,027,000)	(1,144,000)
Net current-period other comprehensive income (loss)						5,094,000	2,450,000
Ending balance		7,403,000		1,116,000		7,403,000	1,116,000
Accumulated (Gain) Loss from Interest Rate Swap Cash Flows Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (10,000)		$ (28,000)		$ (28,000)	(28,000)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						55,000	23,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax						(37,000)	(33,000)
Net current-period other comprehensive income (loss)						18,000	(10,000)
Ending balance		$ (10,000)		$ (10,000)		$ (10,000)	$ (10,000)