FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Changes in Measurements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 17,574	$ 16,061
Other Changes in Fair Value from Continuing and New Contracts, Net	9,403	(2,268)
Settlements	(7,999)	(5,516)
Balance at end of period	18,978	8,277
SJG
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	5,035	4,928
Other Changes in Fair Value from Continuing and New Contracts, Net	4,806	1,706
Settlements	(5,035)	(4,928)
Balance at end of period	$ 4,806	$ 1,706