FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Changes in Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 17,401	$ (2,096)	$ 9,035	$ (632)
Other Changes in Fair Value from Continuing and New Contracts, Net	1,352	10,404	8,346	8,346
Transfers out of Level 3	(206)		(954)
Settlements	(4,781)	(423)	(2,661)	171
Balance at end of period	13,766	7,885	13,766	7,885
SJG
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	6,933	(224)	926	183
Other Changes in Fair Value from Continuing and New Contracts, Net	(1,603)	730	5,330	506
Transfers out of Level 3	(206)		(206)
Settlements	0	0	(926)	(183)
Balance at end of period	$ 5,124	$ 506	$ 5,124	$ 506