Acquisitions - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended								12 Months Ended			0 Months Ended				6 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	May 31, 2013 customer	Dec. 02, 2013	Jun. 07, 2013	Feb. 05, 2013 customer	Jun. 30, 2015	Aug. 30, 2010	Jan. 30, 2015 mi
Cash paid for acquisition									$ 0	$ 20,201,000	$ 124,000
Regulatory Assets	87,103,000				69,020,000				87,103,000	69,020,000
Revenues	120,380,000	91,619,000	100,497,000	186,337,000	122,887,000	86,545,000	94,146,000	140,729,000	498,834,000	444,306,000	392,502,000
Net Income	10,097,000	3,180,000	5,134,000	17,681,000	9,683,000	3,879,000	4,356,000	14,869,000	36,092,000	32,787,000	28,863,000
Goodwill	4,952,000				4,354,000				4,952,000	4,354,000
Asset Impairment Charges									6,881,000	0	0
Eastern Shore Gas Company
Cash paid for acquisition												16,500,000
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
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
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory												384,000
Business Combination, Acquired Receivables, Fair Value												2,500,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities												(227,000)
Revenues									24,300,000	9,800,000
Net Income									2,500,000	309,000
Fort Meade
Cash paid for acquisition													792,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment													92,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory													14,000
Regulatory Assets													14,000
Goodwill													714,000				714,000
Goodwill, Purchase Accounting Adjustments									564,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other													42,000
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments	578,000								578,000
Austin Cox
Cash paid for acquisition														600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment														105,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory														30,000
Goodwill														237,000
Asset Impairment Charges									412,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles														250,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life														5 years
Propane Acquisitions
Cash paid for acquisition															2,900,000
Number of residential and commercial customers receiving propane gas distribution service															3,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment															1,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory															231,000
Goodwill, Purchase Accounting Adjustments									271,000
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Inventory									271,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles															300,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life															12 years
Glades
Goodwill	724,000								724,000
BravePoint Group [Member]
Revenues									15,100,000	19,100,000	17,500,000
Net Income									(232,000)	(155,000)	454,000
Gatherco [Member]
Cash paid for acquisition																27,600,000
Business Combination Recognized Identifiable Assets Acquired And Liabilities To Be Assumed Long Term Debt																		1,700,000
Number Of Gathering Stations																		16
Number of Pipeline Miles																		2,000.0
Number of Producers Served																		300
Number of Customers Served																		6,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned																		$ 29,900,000
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares																0.6