FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Changes in Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 18,979	$ 8,277	$ 17,574	$ 16,061
Other Changes in Fair Value from Continuing and New Contracts, Net	(2,386)	6,553	7,017	4,285
Settlements	(4,342)	(4,870)	(12,340)	(10,386)
Balance at end of period	12,251	9,960	12,251	9,960
SJG
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	4,806	1,706	5,035	4,928
Other Changes in Fair Value from Continuing and New Contracts, Net	(441)	2	4,365	1,708
Settlements	0	0	(5,035)	(4,928)
Balance at end of period	$ 4,365	$ 1,708	$ 4,365	$ 1,708