FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Changes in Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 16,234	$ 13,241	$ 9,035	$ (632)
Other Changes in Fair Value from Continuing and New Contracts, Net	7,982	(12,073)	6,994	(2,058)
Transfers out of Level 3	(748)		(748)
Settlements	(6,067)	(3,264)	2,120	594
Balance at end of period	17,401	(2,096)	17,401	(2,096)
SJG
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	511	(4)	926	183
Other Changes in Fair Value from Continuing and New Contracts, Net	6,422	(220)	6,933	(224)
Settlements	0	0	(926)	(183)
Balance at end of period	$ 6,933	$ (224)	$ 6,933	$ (224)