Segment Information - Schedule of Segment Reporting Information by Segment (Detail) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments				2
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers		$ 131,053	$ 107,335	$ 493,403	$ 409,604
Operating Income
Total operating income		18,648	20,113	99,981	94,288
Other expense, net		957	327	4,454	2,155
Interest		6,240	4,975	17,404	15,134
Income Before Income Taxes		13,365	15,465	87,031	81,309
Income Taxes		3,703	2,990	23,385	20,555
Net Income		9,662	12,475	63,646	60,754
Identifiable Assets
Total identifiable assets		2,157,422		2,157,422		$ 2,114,869
Regulated Energy [Member]
Operating Income
Total operating income		23,663	23,370	84,202	78,835
Identifiable Assets
Total identifiable assets		1,665,205		1,665,205		1,629,191
Unregulated Energy [Member]
Operating Income
Total operating income		(5,056)	(2,952)	15,557	15,624
Identifiable Assets
Total identifiable assets		441,843		441,843		439,114
Other [Member]
Identifiable Assets
Total identifiable assets		50,374		50,374		$ 46,564
Other and eliminations [Member]
Operating Income
Total operating income		41	(305)	222	(171)
Operating Revenues, Unaffiliated Customers [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers		131,053	107,335	493,403	409,604
Operating Revenues, Unaffiliated Customers [Member] | Regulated Energy [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers		90,270	79,892	306,159	280,987
Operating Revenues, Unaffiliated Customers [Member] | Unregulated Energy [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers		40,783	27,443	187,244	128,617
Intersegment Revenues [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers	[1]	7,886	5,302	20,592	14,937
Intersegment Revenues [Member] | Regulated Energy [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers	[1]	710	504	4,905	1,516
Intersegment Revenues [Member] | Unregulated Energy [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers	[1]	7,131	4,666	14,950	13,024
Intersegment Revenues [Member] | Other [Member]
Operating Revenues, Unaffiliated Customers
Total operating revenues, unaffiliated customers	[1]	45	132	737	397
Retained Earnings [Member]
Operating Income
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent		9,662	12,475	63,646	60,754
Net Income		$ 9,662	$ 12,475	$ 63,646	$ 60,754

[1] All significant intersegment revenues are billed at market rates and have been eliminated from consolidated operating revenues.