Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 02, 2013	Feb. 05, 2013	Aug. 30, 2010	Oct. 31, 2009
Goodwill [Line Items]
Goodwill	$ 15,070	$ 14,548
Amortization of intangible assets	380	367	$ 396
Amortization of intangible assets, 2017	366
Amortization of intangible assets, 2018	353
Amortization of intangible assets, 2019	353
Amortization of intangible assets, 2020	353
Amortization of intangible assets, 2021	288
Regulated Energy
Goodwill [Line Items]
Goodwill	3,353	3,353
Unregulated Energy
Goodwill [Line Items]
Goodwill	11,717	$ 11,195			$ 1,600
FPU | Regulated Energy
Goodwill [Line Items]
Goodwill							$ 2,500
Indiantown Gas Company | Regulated Energy
Goodwill [Line Items]
Goodwill						$ 170
Fort Meade
Goodwill [Line Items]
Goodwill				$ 714
Gatherco
Goodwill [Line Items]
Goodwill	10,119
Gatherco | Unregulated Energy
Goodwill [Line Items]
Goodwill	$ 10,100
Anderson Gas
Goodwill [Line Items]
Amortized period of acquired intangible assets	6 years
Virginia LP Gas, Inc.
Goodwill [Line Items]
Amortized period of acquired intangible assets	7 years
Virginia LP Gas, Inc. | Maximum
Goodwill [Line Items]
Amortized period of acquired intangible assets	40 years
Customer list | Minimum
Goodwill [Line Items]
Amortized period of acquired intangible assets	7 years
Customer list | Maximum
Goodwill [Line Items]
Amortized period of acquired intangible assets	12 years