ACCUMULATED OTHER COMPREHENSIVE LOSS (AOCL) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		$ 1,192,409	$ 1,289,240	$ 1,037,539
Other comprehensive income before reclassifications		10,636
Amounts reclassified from AOCL		34
Other Comprehensive Income (Loss) - Net of Tax		10,670	(9,384)	(2,882)
Ending balance		1,267,022	1,192,409	1,289,240
Postretirement Liability Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	[1]	(36,262)	(25,342)	(22,145)
Other comprehensive income before reclassifications		10,636
Amounts reclassified from AOCL		0
Other Comprehensive Income (Loss) - Net of Tax	[1]	10,636	(10,920)	(3,197)
Ending balance	[1]	(25,626)	(36,262)	(25,342)
Unrealized Gain (Loss) on Derivatives-Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(396)
Other comprehensive income before reclassifications		0
Amounts reclassified from AOCL		34
Other Comprehensive Income (Loss) - Net of Tax		34
Ending balance		(362)	(396)
Unrealized Gain (Loss) on Available- for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(10)
Other comprehensive income before reclassifications		0
Amounts reclassified from AOCL		0
Other Comprehensive Income (Loss) - Net of Tax		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)
Other comprehensive income before reclassifications		0
Amounts reclassified from AOCL		0
Other Comprehensive Income (Loss) - Net of Tax		0
Ending balance		(97)	(97)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(36,765)	(27,381)	(24,499)
Other Comprehensive Income (Loss) - Net of Tax		10,670	(9,384)	(2,882)
Ending balance		(26,095)	(36,765)	(27,381)
South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		921,433	839,900	707,927
Other comprehensive income before reclassifications		3,606
Amounts reclassified from AOCL		34
Other Comprehensive Income (Loss) - Net of Tax		3,640	(11,063)	(2,072)
Ending balance		1,008,022	921,433	839,900
South Jersey Gas Company | Postretirement Liability Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	[1]	(25,507)	(14,417)	(12,220)
Other comprehensive income before reclassifications		3,606
Amounts reclassified from AOCL		0
Other Comprehensive Income (Loss) - Net of Tax	[1]	3,606	(11,090)	(2,197)
Ending balance	[1]	(21,901)	(25,507)	(14,417)
South Jersey Gas Company | Unrealized Gain (Loss) on Derivatives-Other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(490)
Other comprehensive income before reclassifications		0
Amounts reclassified from AOCL		34
Other Comprehensive Income (Loss) - Net of Tax		34
Ending balance		(456)	(490)
South Jersey Gas Company | Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(25,997)	(14,934)	(12,862)
Other Comprehensive Income (Loss) - Net of Tax		3,640	(11,063)	(2,072)
Ending balance		$ (22,357)	$ (25,997)	$ (14,934)
Postretirement Liability
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Combined average statutory tax rate		25.00%	27.00%	40.00%
Postretirement Liability | South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Combined average statutory tax rate		25.00%	27.00%	40.00%
Unrealized Gain (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Combined average statutory tax rate		25.00%	39.00%	40.00%
Unrealized Gain (Loss) | South Jersey Gas Company
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Combined average statutory tax rate		25.00%	39.00%	40.00%

[1] Determined using a combined average statutory tax rate of 25% in 2018; 27% for 2017; and 40% for 2016.