Acquisitions - Additional Information (Detail) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) Dekatherm	Dec. 31, 2019 USD ($)
Cash paid for acquisition									$ 36,371	$ 22,231	$ 23,988
Revenues									569,968	488,198	479,605
Operating Income (Loss)									131,112	112,723	106,285
Net Income	$ 22,352	$ 9,261	$ 10,956	$ 28,930	$ 22,564	$ 5,621	$ 8,304	$ 28,663	83,466	71,498	65,153
Elkton Gas [Member]
Revenues									7,105	$ 2,399
Marlin Gas Services [Member]
Additional Compressed Natural Gas Deliverability | Dekatherm										7,000
Regulated Energy [Member]
Operating Income (Loss)									106,064	$ 92,124	86,584
Regulated Energy [Member] | Elkton Gas [Member]
Operating Income (Loss)									$ 1,000	418
Number of customers acquired through acquisition									7,000
Business Combination, Consideration Transferred									$ 15,600
Business Combination, Working Capital	600								600
Property, Plant and Equipment, Acquired During Period	15,900								15,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	2,600								2,600
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Regulatory Liabilities									2,600
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	4,300								4,300
Unregulated Energy
Operating Income (Loss)									24,382	20,664	$ 19,938
Unregulated Energy | Western Natural Gas [Member]
Revenues									2,594	555
Operating Income (Loss)									550	$ 120
Business Combination, Consideration Transferred									6,700
Business Combination, Working Capital	300								300
Property, Plant and Equipment, Acquired During Period	3,500								3,500
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	1,800								1,800
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	1,400								1,400
Unregulated Energy | Diversified Energy
Revenues									1,423
Operating Income (Loss)									$ 300
Number of customers acquired through acquisition									19,000
Business Combination, Consideration Transferred									$ 37,500
Business Combination, Working Capital	1,700								1,700
Business Combination, Contingent Consideration, Liability	2,100								2,100
Property, Plant and Equipment, Acquired During Period	23,100								23,100
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	5,900								5,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Indefinite-Lived Intangible Assets	6,200								6,200
Business Acquisition, Preacquisition Contingency, Amount of Settlement	$ 800								$ 800
Gallons acquired through acquisition									10,000,000