FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Quantitative Information Regarding Significant Unobservable Inputs (Details) - Forward Contracts - Fair Value, Inputs, Level 3 $ in Thousands	Sep. 30, 2017 USD ($) $ / decatherm	Dec. 31, 2016 USD ($) $ / decatherm
Natural Gas | Minimum
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	1.05	1.03
Natural Gas | Minimum | South Jersey Gas Company
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	2.37	3.25
Natural Gas | Maximum
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	8.37	11.33
Natural Gas | Maximum | South Jersey Gas Company
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	6.42	6.33
Natural Gas | Weighted Average
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	2.87	2.71
Natural Gas | Weighted Average | South Jersey Gas Company
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Forward price (in dollars per dt) | $ / decatherm	4.60	5.09
Electricity | Minimum | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	36.36%	21.43%
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	63.64%	78.57%
Electricity | Weighted Average | On-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	52.98%	55.14%
Electricity | Weighted Average | Off-Peak
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Fixed electric load profile	47.02%	44.86%
Discounted Cash Flow | Natural Gas
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	$ 17,545	$ 23,301
Liabilities | $	7,587	18,109
Discounted Cash Flow | Natural Gas | South Jersey Gas Company
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	6,918	1,040
Liabilities | $	1,794	114
Discounted Cash Flow | Electricity
Fair Value Inputs, Assets And Liabilities, Quantitative Information [Line Items]
Assets | $	6,927	11,784
Liabilities | $	$ 3,119	$ 7,941