DERIVATIVE INSTRUMENTS - Fair Value of all Derivative Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Assets	$ 36,654	$ 48,127
Liabilities	24,359	63,333
South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	404	7,332
Liabilities	7,118	16,468
Commodity Contract
Derivatives, Fair Value [Line Items]
Assets	36,654	48,127
Liabilities	0	0
Commodity Contract | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	404	7,332
Liabilities	0	0
Derivatives not designated as hedging instruments under GAAP
Derivatives, Fair Value [Line Items]
Assets	36,654	48,127
Liabilities	24,359	63,333
Derivatives not designated as hedging instruments under GAAP | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	404	7,332
Liabilities	7,118	16,468
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Current
Derivatives, Fair Value [Line Items]
Assets	24,386	42,139
Liabilities	12,486	46,938
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	404	7,327
Liabilities	784	9,270
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Non-Current
Derivatives, Fair Value [Line Items]
Assets	12,268	5,988
Liabilities	4,153	6,025
Derivatives not designated as hedging instruments under GAAP | Commodity Contract | Derivatives - Energy Related - Non-Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	0	5
Liabilities	328	170
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Current
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	526	748
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Current | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	337	389
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Noncurrent
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	7,194	9,622
Derivatives not designated as hedging instruments under GAAP | Interest rate contracts | Derivatives - Other - Noncurrent | South Jersey Gas Company
Derivatives, Fair Value [Line Items]
Assets	0	0
Liabilities	$ 5,669	$ 6,639