Stockholder's Equity - Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Loss (Detail) - USD ($) shares in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Amortization of pension and postretirement items:
Tax benefit		$ (13,506,000)	$ (12,401,000)
Derivative, Gain (Loss) on Derivative, Net		$ 3,491,000	3,253,000
Stock Issued During Period, Shares, Dividend Reinvestment Plan		0.1		0.1
Stock Issued During Period, Value, Dividend Reinvestment Plan		$ 137.45		$ 125.71
Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan		3,200,000		$ 15,200,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Amortization of pension and postretirement items:
Net of tax		1,951,000	2,145,000
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
Net loss	[1]	(43,000)	(104,000)
Total before tax		(24,000)	(85,000)
Tax benefit		6,000	22,000
Net of tax		(18,000)	(63,000)
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		(752,000)	(842,000)
Net of tax		1,969,000	2,205,000
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			4,000
Tax benefit		0	(1,000)
Net of tax		0	3,000
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]	2,721,000	3,047,000
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	$ 4,000

[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.