Income Taxes - Schedule of Accumulated Deferred Income Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosure Income Taxes Schedule Of Accumulated Deferred Income Tax Assets And Liabilities [Abstract]
Deferred State and Local Income Tax Expense (Benefit)	$ 8,200	$ 4,900	$ 4,700
Deferred income tax liabilities:
Property, plant and equipment	224,034	199,287
Acquisition adjustment	6,266	6,618
Deferred Tax Liabilities Loss On Reacquired Debt	183	201
Deferred Income Tax Liability - Deferred Gas Costs	2,366	509
Deferred Income Tax Liability, Natural Gas Conversion Costs	5,529	5,379
Deferred Income Tax Liability, Storm Reserve	5,783	7,073
Other	6,301	5,587
Total deferred income tax liabilities	250,462	224,654
Deferred income tax assets:
Pension and other employee benefits	5,354	4,636
Environmental costs	996	1,064
Net operating loss carryforwards	1,490	1,587
Storm reserve liability	448	409
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals	4,843	6,153
Other	3,781	5,417
Total deferred income tax assets	16,912	19,266
Deferred income taxes	$ 233,550	$ 205,388