Income Taxes - Schedule of Income Tax Expense (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Current Income Tax Expense
Federal		$ 8,284	$ 2,775	$ (2,777)
State		1,948	(96)	2,162
Other		(47)	(47)	(47)
Total current income tax expense (benefit)		10,185	2,632	(662)
Deferred Income Tax Expense (1)
Total deferred income tax expense	[1]	23,647	26,599	24,200
Income Tax Expense from Continuing Operations		33,832	29,231	23,538
Discontinued Operation, Tax Effect of Gain (Loss) from Disposal of Discontinued Operation		0	0	153
Income Tax Expense (Benefit), Continuing Operations, Discontinued Operations		33,832	29,231	23,691
Deferred State and Local Income Tax Expense (Benefit)		7,800	8,200	4,900
Property, plant and equipment
Deferred Income Tax Expense (1)
Total deferred income tax expense		14,968	24,074	23,224
Deferred gas costs
Deferred Income Tax Expense (1)
Total deferred income tax expense		8,923	1,857	(714)
Pensions and other employee benefits
Deferred Income Tax Expense (1)
Total deferred income tax expense		1,109	(655)	(75)
FPU merger related premium cost and deferred gain
Deferred Income Tax Expense (1)
Total deferred income tax expense		(351)	(351)	156
Net operating loss carryforwards
Deferred Income Tax Expense (1)
Total deferred income tax expense		2	97	5,107
Other
Deferred Income Tax Expense (1)
Total deferred income tax expense		$ (1,004)	$ 1,577	$ (3,498)

[1] (1) Includes $7.8 million, $8.2 million, and $4.9 million of deferred state income taxes for the years 2022, 2021 and 2020, respectively.