Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended	1 Months Ended			12 Months Ended
	Dec. 31, 2012 Eastern Shore Gas Company [Member] Customer	Dec. 31, 2012 Natural Gas Acquisition [Member]	Aug. 09, 2010 Natural Gas Acquisition [Member] Customer	Feb. 04, 2010 Propane Acquisitions [Member] Customer	Dec. 31, 2012 Propane Acquisitions [Member] Customer	Feb. 28, 2013 Propane Acquisitions [Member] Subsequent Event [Member]	Dec. 31, 2012 Propane Acquisitions [Member] Crescent Propane, Inc. (Crescent) and Barefoot Bay Propane Gas Company [Member]
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	$ 16,500,000		$ 1,200,000	$ 600,000		$ 2,700,000	$ 954,000
Number of retail customers			700	1,000
Goodwill acquired due to merger		742,000					200,000
Amortization period of merger cost		15 years		7 years
Number of retail customers			700	1,000
Purchase price	16,500,000		1,200,000	600,000		2,700,000	954,000
Cash paid for acquisition				300,000
Total value of consideration remaining amount to be paid				300,000
Total value of consideration remaining amount payment term, months				60 months
Purchase price allocation of intangible assets				$ 188,000
Number of residential and commercial customers receiving propane gas distribution service	11,000				3,000