DERIVATIVE INSTRUMENTS (Details) (USD $)						3 Months Ended				9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2005	Sep. 30, 2012 Natural Gas (in MMdts) [Member] Derivative Transaction Type, Purchase [Member] millions_of_decatherms	Sep. 30, 2012 Natural Gas (in MMdts) [Member] Derivative Transaction Type, Sale [Member] millions_of_decatherms	Sep. 30, 2012 South Jersey Resource Group [Member]		Sep. 30, 2011 South Jersey Resource Group [Member]		Sep. 30, 2012 South Jersey Resource Group [Member]		Sep. 30, 2011 South Jersey Resource Group [Member]
Derivative [Line Items]
Outstanding derivative contracts notional amount				7.2	0.8
Unrealized losses included in its BGSS related to open financial contracts	$ 2,100,000	$ 10,200,000
Initial cost of Treasury Locks			1,400,000
Amortization period of Treasury Locks			30 years
Unamortized balance of Treasury Locks	1,100,000	1,100,000
Net realized losses associated with SJG's energy-related financial commodity contracts						$ 3,011,000	[1]	$ 2,404,000	[1]	$ 13,666,000	[1]	$ 9,458,000	[1]

[1] Contracts used to hedge natural gas purchases. Included in Cost of Sales on the Condensed Statement of Income.