Goodwill and Other Intangible Assets - Schedule of Carrying Value of Goodwill (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		$ 13,777	$ 12,365
Finite-Lived Intangible Assets, Accumulated Amortization		5,485	4,236
Goodwill		38,731	32,668
Goodwill, Transfers	[1]	6,063
Regulated Energy
Goodwill [Line Items]
Goodwill		7,617	3,353
Goodwill, Transfers	[1]	4,264
Unregulated Energy
Goodwill [Line Items]
Goodwill		31,114	29,315
Goodwill, Transfers	[1]	1,799
Customer Lists [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	[2]	10,680	9,391
Finite-Lived Intangible Assets, Accumulated Amortization	[2]	4,269	3,463
Noncompete Agreements [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	[2]	2,375	2,252
Finite-Lived Intangible Assets, Accumulated Amortization	[2]	768	451
Patents [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		452	452
Finite-Lived Intangible Assets, Accumulated Amortization		236	118
Other Intangible Assets [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		270	270
Finite-Lived Intangible Assets, Accumulated Amortization		$ 212	$ 204

[1] (1)Includes goodwill from the purchase of operating assets of Elkton Gas in the third quarter of 2020 and Western Natural Gas in October 2020.

[2] 1) The customer relationship and non-compete agreements amounts includes $1.3 million and $0.1 million, respectively, recorded as a result of the purchase of the operating assets of Western Natural Gas in October 2020. The amounts also include customer relationship and non-compete agreements amounts of $4.6 million and $0.5 million, respectively, recorded as a result of the purchase of the operating assets of Boulden in December 2019.