Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		$ 13,777	$ 12,365
Acquired finite-lived intangible assets, weighted average useful life		11 years
Goodwill		$ 38,731	32,668
Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months		1,300
Amortization of intangible assets		1,200	800	$ 400
Amortization of intangible assets, 2020		900
Amortization of intangible assets, 2019		1,000
Regulated Energy
Goodwill [Line Items]
Goodwill		7,617	3,353
Unregulated Energy
Goodwill [Line Items]
Goodwill		31,114	29,315
Customer list
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	$ 10,680	9,391
Customer list | Minimum [Member]
Goodwill [Line Items]
Amortized period of acquired intangible assets		5 years
Customer list | Boulden [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		$ 4,600
Customer list | Western Natural Gas [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		1,300
Noncompete Agreements [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	[1]	2,375	$ 2,252
Noncompete Agreements [Member] | Boulden [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		500
Noncompete Agreements [Member] | Western Natural Gas [Member]
Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross		$ 100

[1] 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.