PENSION AND OTHER POSTRETIREMENT BENEFITS - DETAILS OF ACTIVITY WITHIN THE REGULATORY ASSET AND ACCUMULATED OTHER COMPREHENSIVE LOSS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Regulatory Assets
Beginning Balance	$ 61,584	$ 67,539
Amounts Arising during the Period: Net Actuarial (Loss) Gain	17,377	(404)
Amounts Arising during the Period: Prior Service Credit	0
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(6,337)	(5,456)
Amounts Amortized to Net Periodic Costs: Prior Service Cost	(95)	(95)
Ending Balance	72,529	61,584
Accumulated Other Comprehensive Loss  (pre-tax)
Beginning Balance	51,285	42,525
Amounts Arising during the Period: Net Actuarial (Loss) Gain	11,459	12,865
Amounts Arising during the Period: Prior Service Credit	0
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(5,244)	(4,094)
Amortization to Net Periodic Costs: Prior Service (Credits) Costs	(11)	(11)
Ending Balance	57,489	51,285
Other Postretirement Benefits
Regulatory Assets
Beginning Balance	12,251	15,219
Amounts Arising during the Period: Net Actuarial (Loss) Gain	1,718	(2,400)
Amounts Arising during the Period: Prior Service Credit	(436)
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(672)	(1,042)
Amounts Amortized to Net Periodic Costs: Prior Service Cost	502	474
Ending Balance	13,363	12,251
Accumulated Other Comprehensive Loss  (pre-tax)
Beginning Balance	964	687
Amounts Arising during the Period: Net Actuarial (Loss) Gain	2,194	311
Amounts Arising during the Period: Prior Service Credit	(317)
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(180)	(121)
Amortization to Net Periodic Costs: Prior Service (Credits) Costs	107	87
Ending Balance	2,768	964
South Jersey Gas Company | Pension Benefits
Regulatory Assets
Beginning Balance	60,668	65,493
Amounts Arising during the Period: Net Actuarial (Loss) Gain	10,595	726
Amounts Arising during the Period: Prior Service Credit	0
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(5,492)	(5,456)
Amounts Amortized to Net Periodic Costs: Prior Service Cost	(95)	(95)
Ending Balance	65,676	60,668
Accumulated Other Comprehensive Loss  (pre-tax)
Beginning Balance	42,190	34,396
Amounts Arising during the Period: Net Actuarial (Loss) Gain	9,119	10,562
Amounts Arising during the Period: Prior Service Credit	0
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(3,872)	(2,768)
Amortization to Net Periodic Costs: Prior Service (Credits) Costs	0	0
Ending Balance	47,437	42,190
South Jersey Gas Company | Other Postretirement Benefits
Regulatory Assets
Beginning Balance	11,342	14,628
Amounts Arising during the Period: Net Actuarial (Loss) Gain	1,014	(2,718)
Amounts Arising during the Period: Prior Service Credit	(436)
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	(672)	(1,042)
Amounts Amortized to Net Periodic Costs: Prior Service Cost	502	474
Ending Balance	11,750	11,342
Accumulated Other Comprehensive Loss  (pre-tax)
Beginning Balance	0	0
Amounts Arising during the Period: Net Actuarial (Loss) Gain	0	0
Amounts Arising during the Period: Prior Service Credit	0
Amounts Amortized to Net Periodic Costs: Net Actuarial Loss	0	0
Amortization to Net Periodic Costs: Prior Service (Credits) Costs	0	0
Ending Balance	$ 0	$ 0