ACCUMULATED OTHER COMPREHENSIVE LOSS - Summary of Changes (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				$ 1,289,240
Other comprehensive income before reclassifications		$ 0		0
Amounts reclassified from AOCL		7		1,522
Other Comprehensive Income - Net of Tax	[1]	7	$ 104	1,522	$ 204
Ending balance		$ 1,279,249		$ 1,279,249
Combined statutory tax rate		40.00%	40.00%	40.00%	40.00%
South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance				$ 839,900
Other comprehensive income before reclassifications		$ 0		0
Amounts reclassified from AOCL		7		14
Other Comprehensive Income - Net of Tax	[2]	7	$ 10	14	$ 21
Ending balance		$ 928,695		$ 928,695
Combined statutory tax rate		40.00%	40.00%	40.00%	40.00%
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ (25,866)		$ (27,381)
Ending balance		(25,859)		(25,859)
Postretirement Liability Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(25,342)		(25,342)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		0		0
Other Comprehensive Income - Net of Tax		0		0
Ending balance		(25,342)		(25,342)
Unrealized Gain (Loss) on Derivatives-Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(417)		(1,932)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		7		1,522
Other Comprehensive Income - Net of Tax		7		1,522
Ending balance		(410)		(410)
Unrealized Gain (Loss) on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(10)		(10)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		0		0
Other Comprehensive Income - Net of Tax		0		0
Ending balance		(10)		(10)
Other Comprehensive Income (Loss) of Affiliated Companies
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(97)		(97)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		0		0
Other Comprehensive Income - Net of Tax		0		0
Ending balance		(97)		(97)
Total | South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(14,927)		(14,934)
Ending balance		(14,920)		(14,920)
Postretirement Liability Adjustment | South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(14,417)		(14,417)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		0		0
Other Comprehensive Income - Net of Tax		0		0
Ending balance		(14,417)		(14,417)
Unrealized Gain (Loss) on Derivatives-Other | South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(510)		(517)
Other comprehensive income before reclassifications		0		0
Amounts reclassified from AOCL		7		14
Other Comprehensive Income - Net of Tax		7		14
Ending balance		$ (503)		$ (503)

[1] Determined using a combined average statutory tax rate of 40%.

[2] Determined using a combined average statutory tax rate of 40%.