FAIR VALUE OF FINANCIAL ASSETS AND FINANCIAL LIABILITIES - Changes in Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	$ 12,251	$ 9,959	$ 17,574	$ 16,061
Other Changes in Fair Value from Continuing and New Contracts, Net	(3,198)	6,046	3,819	10,331
Settlements	(2,644)	(4,144)	(14,984)	(14,531)
Balance at end of period	6,409	11,861	6,409	11,861
SJG
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period	4,365	1,708	5,035	4,928
Other Changes in Fair Value from Continuing and New Contracts, Net	(61)	6,533	4,304	8,241
Settlements	0	0	(5,035)	(4,928)
Balance at end of period	$ 4,304	$ 8,241	$ 4,304	$ 8,241