Acquisitions - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	2 Months Ended	3 Months Ended																12 Months Ended			0 Months Ended	12 Months Ended	0 Months Ended		0 Months Ended
	May 31, 2013 storage_tank gal	May 31, 2013 storage_tank gal	Jan. 31, 2012	Dec. 31, 2013 gal		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013 gal	Dec. 31, 2012	Dec. 31, 2011	May 31, 2013 Eastern Shore Gas Company customer	Dec. 31, 2013 Eastern Shore Gas Company	Dec. 02, 2013 Fort Meade	Aug. 30, 2010 Fort Meade	Jun. 07, 2013 Austin Cox	May 31, 2013 Natural Gas Acquisition	Feb. 05, 2013 Propane Acquisitions customer
Cash paid for acquisition			$ 954,000																	$ 20,201,000	$ 124,000	$ 791,000			$ 792,000		$ 600,000	$ 16,500,000	$ 2,900,000
Purchase Price Adjustment						543,000
Business Acquisition, Cost of Acquired Entity, Transaction Costs, Sales Tax						(726,000)
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
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	12,600,000	12,600,000																							670,000		105,000		1,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	344,000	344,000																							14,000		30,000		502,000
Business Combination, Acquired Receivables, Fair Value	2,500,000	2,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	(227,000)	(227,000)
Revenues				122,887,000	[1]	86,545,000	[1]	94,146,000	[1]	140,729,000	[1]	109,516,000	[1]	78,175,000	[1]	83,897,000	[1]	120,914,000	[1]	444,306,000	392,502,000	418,027,000		9,800,000
Net Income				9,683,000	[1]	3,879,000	[1]	4,356,000	[1]	14,869,000	[1]	9,857,000	[1]	3,219,000	[1]	5,060,000	[1]	10,727,000	[1]	32,787,000	28,863,000	27,622,000		309,000
Number Of Years To Purchase Propane Under Contract	6 years	6 years																		6 years
Number of Leased Propane Tanks	13	13
Storage Capacity Of Leased Propane Tanks	570,000	570,000
Capital Lease Obligation Monthly Fee Payment Year1	42,000	42,000
Capital Lease Obligation Monthly Fee Payment Year2 To 6	125,000	125,000
Annual Estimate Of Volume Of Propane To Be Purchased	7,400,000	7,400,000		7,400,000																7,400,000
Capital lease obligation	7,100,000	7,100,000		6,978,000																6,978,000
Capital Leased Assets, Gross	7,100,000	7,100,000
Interest Expense, Lessee, Assets under Capital Lease																				144,000
Amortization of Leased Asset																				147,000
Goodwill			200,000	4,354,000								4,090,000								4,354,000	4,090,000				150,000	150,000	237,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other																									42,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles																											$ 250,000		$ 300,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life																											5 years		12 years

[1] The sum of the four quarters does not equal the total year due to rounding.