REGULATORY ASSETS AND REGULATORY LIABILITIES - Narrative and Regulatory Liabilities (Details) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) site	Jun. 30, 2020 USD ($) site	Dec. 31, 2019 USD ($)
SJG
Regulatory Assets [Line Items]
Regulatory assets	$ 485,354	$ 485,354	$ 496,177
Deferred incremental costs, CARES Act	$ 700	$ 700
SJG | Environmental Remediation
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	12	12
Original recovery period of expenditures		7 years
SJG | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Regulatory assets	$ 0	$ 0	0
SJG | Other Regulatory Assets
Regulatory Assets [Line Items]
Regulatory assets	21,719	21,719	10,678
Increase (decrease) in regulatory assets		10,100
SJG | Judicial Ruling | Pricing dispute, long-term gas supply contract
Regulatory Assets [Line Items]
Amount paid to third party supplier		$ 22,900	22,900
SJG | Unprotected Excess Deferred Income Tax
Regulatory Assets [Line Items]
Period to refund customers		5 years
ETG Utility Operations
Regulatory Assets [Line Items]
Regulatory assets	163,177	$ 163,177	169,231
Deferred incremental costs, CARES Act	$ 9,000	$ 9,000
ETG Utility Operations | Environmental Remediation
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	5	5
ETG Utility Operations | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Regulatory assets	$ (13,615)	$ (13,615)	(20,423)
Increase (decrease) in regulatory assets		(6,800)
ETG Utility Operations | Other Regulatory Assets
Regulatory Assets [Line Items]
Regulatory assets	$ 18,507	$ 18,507	$ 9,004