Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Loss (Detail) - USD ($) shares in Millions		3 Months Ended		6 Months Ended		12 Months Ended
		Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Amortization of pension and postretirement items:
Tax benefit		$ (6,177,000)	$ (5,164,000)	$ (19,683,000)	$ (17,565,000)
Derivative, Gain (Loss) on Derivative, Net		(403,000)	4,804,000	$ 3,088,000	8,057,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan				0.1		0.1
Stock Issued During Period, Value, Dividend Reinvestment Plan				$ 137.24		$ 125.71
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan				4,300,000		$ 15,200,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amortization of pension and postretirement items:
Net of tax		187,000	281,000	2,139,000	2,425,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Amortization of pension and postretirement items:
Prior service cost	[1]	19,000	19,000	38,000	38,000
Net loss	[1]	(43,000)	(106,000)	(86,000)	(209,000)
Total before tax		(24,000)	(87,000)	(48,000)	(171,000)
Tax benefit		6,000	23,000	13,000	43,000
Net of tax		(18,000)	(64,000)	(35,000)	(128,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Amortization of pension and postretirement items:
Tax benefit		(78,000)	(126,000)	(830,000)	(968,000)
Net of tax		205,000	329,000	2,174,000	2,534,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated (Gain) Loss from Interest Rate Swap Cash Flows Hedges [Member]
Amortization of pension and postretirement items:
Other Comprehensive Income Loss Adjustments AOCI Swap Agreements			22,000		26,000
Tax benefit		0	(6,000)	0	(7,000)
Net of tax		0	16,000	0	19,000
Propane Swap Agreement [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Amortization of pension and postretirement items:
Other Comprehensive Income Loss Adjustments AOCI Swap Agreements	[2]	283,000	455,000	3,004,000	3,502,000
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		$ 0	$ 22,000	$ 0	$ 26,000

[1] These amounts are included in the computation of net periodic costs (benefits). See Note 10, Employee Benefit Plans, for additional details.

[2] These amounts are included in the effects of gains and losses from derivative instruments. See Note 13, Derivative Instruments, for additional details.