FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Quantitative Information Regarding Significant Unobservable Inputs (Details) - Forward Contracts - Level 3 $ in Thousands	Jun. 30, 2020 USD ($) $ / decatherm	Dec. 31, 2019 USD ($) $ / decatherm
Natural Gas | Minimum
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	1.27	1.57
Natural Gas | Minimum | SJG
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	1.34	1.85
Natural Gas | Maximum
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	6.47	7.28
Natural Gas | Maximum | SJG
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	4.98	3.61
Natural Gas | Weighted Average
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	2.74	2.38
Natural Gas | Weighted Average | SJG
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	3.72	3.02
Electricity | Minimum | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	40.34%	0.00%
Electricity | Minimum | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	0.00%	0.00%
Electricity | Maximum | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	100.00%	100.00%
Electricity | Maximum | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	59.66%	100.00%
Electricity | Weighted Average | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	58.15%	55.46%
Electricity | Weighted Average | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed Electric Load Profile	41.85%	44.54%
Discounted Cash Flow | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	$ 15,279	$ 21,645
Liabilities | $	2,953	4,333
Discounted Cash Flow | Natural Gas | SJG
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	4,366	5,049
Liabilities | $	1	14
Discounted Cash Flow | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	1,673	3,718
Liabilities | $	$ 1,748	$ 3,456