ACCUMULATED OTHER COMPREHENSIVE LOSS (AOCL) - RECLASSIFICATIONS OUT OF AOCL (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	$ (16,498)	$ (24,765)	$ (5,544)	$ 21,870	$ 19,266	$ 2,807	$ (7,189)	$ 39,267	$ (24,937)	$ 54,151	$ 1,360
Net Income	(4,045)	37,593	7,659	(37,717)	(45,933)	(9,635)	4,827	(68,069)	3,490	(118,810)	(105,107)
Amounts Reclassified from AOCL | Unrealized Loss on Derivatives-Other - interest rate contracts designated as cash flow hedges
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes									(988)
Net Income									1,536
Amounts Reclassified from AOCL | Interest rate contract | Unrealized Loss on Derivatives-Other - interest rate contracts designated as cash flow hedges
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Charges									2,524
South Jersey Gas Company
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	18,046	(3,688)	1,431	29,911	12,554	(2,007)	1,415	27,404	45,700	39,366	36,945
Net Income	$ (29,584)	$ 5,771	$ (2,266)	$ (46,478)	$ (22,899)	$ 3,315	$ (5,043)	$ (44,418)	(72,557)	$ (69,045)	$ (66,578)
South Jersey Gas Company | Amounts Reclassified from AOCL | Unrealized Gain (Loss) on Derivatives-Other (B)
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes									(19)
South Jersey Gas Company | Amounts Reclassified from AOCL | Unrealized Loss on Derivatives-Other - interest rate contracts designated as cash flow hedges
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net Income									27
South Jersey Gas Company | Amounts Reclassified from AOCL | Interest rate contract | Unrealized Gain (Loss) on Derivatives-Other (B)
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest Charges									$ 46
Unrealized Gain (Loss)
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Combined average statutory tax rate									39.00%	40.00%	40.00%
Unrealized Gain (Loss) | South Jersey Gas Company
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Combined average statutory tax rate									39.00%	40.00%	40.00%
Post-Retirement Liability
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Combined average statutory tax rate									27.00%	40.00%	40.00%
Post-Retirement Liability | South Jersey Gas Company
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Combined average statutory tax rate									27.00%	40.00%	40.00%