REGULATORY ASSETS AND REGULATORY LIABILITIES - Narrative and Regulatory Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) site asset	Dec. 31, 2018 USD ($)
Environmental Remediation
Regulatory Assets [Line Items]
Number of regulatory assets | asset	2
Original recovery period of expenditures	7 years
SJG
Regulatory Assets [Line Items]
Regulatory assets	$ 521,016	$ 492,365
Total Regulatory Liabilities	$ 272,531	286,539
SJG | Environmental Remediation
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	12
SJG | Deferred Revenues
Regulatory Assets [Line Items]
Increase in regulatory assets	$ (8,400)
Total Regulatory Liabilities	0
SJG | Unprotected Excess Deferred Income Tax
Regulatory Assets [Line Items]
Total Regulatory Liabilities	$ 26,100
Period to refund customers	5 years
SJG | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Liabilities	$ 0
SJI
Regulatory Assets [Line Items]
Regulatory assets	719,426	662,969
Total Regulatory Liabilities	442,164	478,499
SJI | Deferred Revenues
Regulatory Assets [Line Items]
Increase in regulatory assets	(21,900)
Total Regulatory Liabilities	13
SJI | Deferred ARO Costs
Regulatory Assets [Line Items]
Increase in regulatory assets	17,200
SJI | Energy Efficiency Tracker
Regulatory Assets [Line Items]
Increase in regulatory assets	7,000
SJI | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Liabilities	1,646
ETG Utility Operations
Regulatory Assets [Line Items]
Regulatory assets	196,853	169,921
Total Regulatory Liabilities	$ 166,981	189,336
ETG Utility Operations | Environmental Remediation
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	6
ETG Utility Operations | Deferred Revenues
Regulatory Assets [Line Items]
Total Regulatory Liabilities	$ 13
ETG Utility Operations | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Liabilities	1,646
ELK Utility Operations
Regulatory Assets [Line Items]
Regulatory assets	1,557	683
Total Regulatory Liabilities	2,652	$ 2,624
ELK Utility Operations | Deferred Revenues
Regulatory Assets [Line Items]
Total Regulatory Liabilities	0
ELK Utility Operations | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Liabilities	$ 0