UNUSED LINES OF CREDIT (Details) (USD $)	3 Months Ended	9 Months Ended			9 Months Ended			9 Months Ended		9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 South Jersey Industries Inc [Member]	Sep. 30, 2011 South Jersey Industries Inc [Member] Revolving Credit Facility [Member]		Mar. 31, 2011 South Jersey Industries Inc [Member] Revolving Credit Facility [Member]	Sep. 30, 2011 South Jersey Industries Inc [Member] Line of Credit [Member]	Sep. 30, 2011 South Jersey Gas Company [Member]	Sep. 30, 2011 South Jersey Gas Company [Member] Revolving Credit Facility [Member]	Mar. 31, 2011 South Jersey Gas Company [Member] Revolving Credit Facility [Member]	Mar. 31, 2011 South Jersey Gas Company [Member] Line of Credit [Member]	Sep. 30, 2011 South Jersey Gas Company [Member] Uncommitted Bank Lines [Member]	Sep. 30, 2011 SJG Commerical Paper Program [Member]
Line of Credit Facility [Line Items]
Total facility	$ 550,437,000	$ 550,437,000		$ 330,437,000	$ 300,000,000		$ 200,000,000	$ 30,437,000	$ 220,000,000	$ 200,000,000	$ 100,000,000	$ 40,000,000	$ 20,000,000	$ 200,000,000
Usage	345,845,000	345,845,000		239,345,000	208,908,000			30,437,000	106,500,000	106,500,000			0
Available liquidity	204,592,000	204,592,000		91,092,000	91,092,000			0	113,500,000	93,500,000			20,000,000
Expiration date		August 2015			April 2015	[1]		November 2013		May 2015			Various
Maturity period (in years)					4					4
Financial covenant, ratio of indebtedness to consolidated total capitalization		0.65 to 1
Letters of credit outstanding	83,000,000	83,000,000
Weighted average borrowing cost		1.08%	0.79%
Average borrowings outstanding during the period		209,200,000	179,600,000
Maximum amounts outstanding during the period		$ 271,400,000	$ 264,200,000
Fixed maturities of notes, at maximum number of days	270

[1] Includes letters of credit outstanding in the amount of $83.0 million.