Acquisitions - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended	0 Months Ended	3 Months Ended		9 Months Ended		0 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	May 31, 2013 Eastern Shore Gas Company [Member] customer	Sep. 30, 2014 Eastern Shore Gas Company [Member]	Sep. 30, 2013 Eastern Shore Gas Company [Member]	Sep. 30, 2014 Eastern Shore Gas Company [Member]	Sep. 30, 2013 Eastern Shore Gas Company [Member]	Dec. 02, 2013 Fort Meade [Member]	Feb. 05, 2013 Propane Acquisition [Member] customer	Sep. 30, 2014 Propane Acquisition [Member]
Business Acquisition [Line Items]
Inventory Purchase Accounting Adjustment													$ 271,000
Purchase Price Adjustment								543,000
Number of residential and commercial customers receiving propane gas distribution service						11,000						3,000
Minimum number of customers to whom gas distribution systems and bulk delivery service provided						500
Purchase price allocated to property, plant and equipment						12,600,000					670,000	1,600,000
Purchase price allocated to propane and other inventory						384,000					14,000	231,000
Receivables						2,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net						227,000
Revenues	91,619,000	86,545,000	378,454,000	321,419,000			4,400,000	3,600,000	18,800,000	4,600,000
Net Income (Loss) Attributable to Parent	3,180,000	3,879,000	25,995,000	23,104,000	32,787,000		300,000	200,000	2,100,000	(200,000)
Purchase price allocated to intangible assets related to customer list												300,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life												12 years
Payments to Acquire Businesses, Gross			0	19,367,000		16,500,000					792,000	2,900,000
Sales Tax								726,000
Goodwill	4,625,000		4,625,000		4,354,000						150,000	724,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other											42,000
Goodwill, Purchase Accounting Adjustments													$ 271,000