DERIVATIVE INSTRUMENTS - OUTSTANDING CONTRACTS (Details) $ in Thousands, MWh in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) MWh	Dec. 31, 2017 USD ($) MMcfe	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2005 USD ($)
Derivative [Line Items]
(Losses) gains on energy-related commodity contracts (a)	$ (13,667)			$ 26,935	$ 8,401
Unrealized Gain (Loss) on Derivatives	(677)			647	96
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net	(2,400)
Derivatives not designated as hedging instruments under GAAP
Derivative [Line Items]
(Losses) gains on energy-related commodity contracts (a)	(13,700)			26,900	$ 8,400
South Jersey Gas Company
Derivative [Line Items]
Unrealized Gain (Loss) on Derivatives	2,100			4,400
Interest Rate Cash Flow Hedge, Cost						$ 1,400
Interest Rate Cash Flow Hedge, Unamortized Balance	$ 800	$ 800	$ 800	$ 900
Expected future purchases
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure		2.6	58,800
Expected future purchases | South Jersey Gas Company
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure		0.0	9,700
Expected future sales
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure		2.1	60,300
Expected future sales | South Jersey Gas Company
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure		0.0	700
Basis and index related purchase and sales contracts
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMcfe			47,400
Basis and index related purchase and sales contracts | South Jersey Gas Company
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMcfe			300