ACCUMULATED OTHER COMPREHENSIVE LOSS - Reclassifications out of AOCL (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	$ (10,925)	$ (16,649)	$ 9,378	$ (12,206)
Losses from reclassifications for the period net of tax	9		$ 25
Combined average statutory tax rate			27.00%	27.00%
SJG
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	(3,747)	$ (2,818)	$ 20,620	$ 19,500
Losses from reclassifications for the period net of tax	9		$ 25
Combined average statutory tax rate			27.00%	27.00%
Postretirement Liability Adjustment
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Losses from reclassifications for the period net of tax	0		$ 0
Postretirement Liability Adjustment | SJG
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Losses from reclassifications for the period net of tax	0		0
Unrealized Gain (Loss) on Derivatives-Other
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Losses from reclassifications for the period net of tax	9		25
Unrealized Gain (Loss) on Derivatives-Other | SJG
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Losses from reclassifications for the period net of tax	9		25
Reclassification out of Accumulated Other Comprehensive Income | Amounts Reclassified from AOCL
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	(3)		(10)
Losses from reclassifications for the period net of tax	9		25
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gain (Loss) on Derivatives-Other | SJG
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Income Taxes	(3)		(10)
Losses from reclassifications for the period net of tax	9		25
Interest Charges | Reclassification out of Accumulated Other Comprehensive Income | Amounts Reclassified from AOCL
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Unrealized Loss in on Derivatives - Other - Interest Rate Contracts designated as cash flow hedges	12		35
Interest Charges | Reclassification out of Accumulated Other Comprehensive Income | Unrealized Gain (Loss) on Derivatives-Other | SJG
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Unrealized Loss in on Derivatives - Other - Interest Rate Contracts designated as cash flow hedges	$ 12		$ 35