FINANCIAL INSTRUMENTS (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($) counterparty	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Margin accounts with selected counter-parties to support risk management activities	$ 16,300	$ 1,600
Notes Receivable - Affiliate	$ 13,275	13,275
Number of counter parties | counterparty	2
Estimated fair value of long-term debt, including current maturities	$ 2,690,000	2,910,000
Carrying amount of long-term debt, including current maturities	2,360,000	2,840,000
Unamortized debt issuance costs	25,700	27,000
Debt discount	5,300
Supplier Concentration Risk | Derivatives Energy Related Assets
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current and non current derivatives	$ 17,300
Percentage of current and non current derivatives	30.70%
Energenic US LLC
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes Receivable - Affiliate	$ 13,600
SJG
Accounts, Notes, Loans and Financing Receivable [Line Items]
Margin accounts with selected counter-parties to support risk management activities	2,100	1,300
Estimated fair value of long-term debt, including current maturities	934,200	895,100
Carrying amount of long-term debt, including current maturities	893,900	893,400
Unamortized debt issuance costs	6,400	6,800
SJG | Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Carrying amount of loans, net of unamortized discounts	4,100	5,300
Imputed interest of loans	$ 500	$ 700
SJG | Financing Receivable | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of note	5 years
SJG | Financing Receivable | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Initial term of note	10 years