PENSION AND OTHER POSTRETIREMENT BENEFITS - RECONCILIATIONS (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in Plan Assets:
Employer Contributions	$ 0	$ 0	$ 0
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,704,000)	(3,727,000)
Noncurrent Liabilities	(135,023,000)	(114,055,000)
South Jersey Gas Company
Change in Plan Assets:
Employer Contributions	0	0	0
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,669,000)	(3,693,000)
Noncurrent Liabilities	(116,973,000)	(99,981,000)
Pension Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	439,373,000	402,156,000
Service Cost	5,871,000	5,583,000	6,442,000
Interest Cost	15,017,000	17,294,000	13,778,000
Actuarial Loss	48,316,000	44,047,000
Retiree Contributions	0	0
Plan Amendments	0	955,000
Benefits Paid	(19,569,000)	(30,662,000)
Settlement	(7,160,000)	0
Benefit Obligation at End of Year	481,848,000	439,373,000	402,156,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	312,497,000	287,220,000
Actual Return on Plan Assets	41,344,000	51,812,000
Employer Contributions	3,875,000	4,127,000
Retiree Contributions	0	0
Benefits Paid	(19,569,000)	(30,662,000)
Settlement	(7,160,000)	0
Fair Value of Plan Assets at End of Year	330,987,000	312,497,000	287,220,000
Funded Status at End of Year	(150,861,000)	(126,876,000)
Accrued Net Benefit (Cost) Credit at End of Year	(151,356,000)	(126,878,000)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,704,000)	(3,727,000)
Noncurrent Liabilities	(147,652,000)	(123,151,000)
Net Amount Recognized at End of Year	(151,356,000)	(126,878,000)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	197,000	292,000
Net Actuarial Loss	72,332,000	61,292,000
Amount Recognized in Regulatory Assets	72,529,000	61,584,000	67,539,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs (Credits)	22,000	32,000
Net Actuarial Loss	57,467,000	51,253,000
Amount Recognized in Accumulated Other Comprehensive Loss	57,489,000	51,285,000	42,525,000
Projected benefit obligation	388,300,000	354,900,000
Accumulated benefit obligation	370,200,000	335,600,000
Pension Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	286,517,000	264,823,000
Service Cost	3,797,000	3,621,000	5,073,000
Interest Cost	9,695,000	11,067,000	10,010,000
Actuarial Loss	27,561,000	24,020,000
Retiree Contributions	0	0
Plan Amendments	3,464,000	0
Benefits Paid	(12,772,000)	(17,014,000)
Benefit Obligation at End of Year	318,262,000	286,517,000	264,823,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	170,959,000	160,285,000
Actual Return on Plan Assets	19,914,000	23,760,000
Employer Contributions	3,840,000	3,927,000
Retiree Contributions	0	0
Benefits Paid	(12,773,000)	(17,013,000)
Fair Value of Plan Assets at End of Year	181,940,000	170,959,000	160,285,000
Funded Status at End of Year	(136,322,000)	(115,558,000)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,669,000)	(3,693,000)
Noncurrent Liabilities	(132,653,000)	(111,865,000)
Net Amount Recognized at End of Year	(136,322,000)	(115,558,000)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	197,000	292,000
Net Actuarial Loss	65,479,000	60,376,000
Amount Recognized in Regulatory Assets	65,676,000	60,668,000	65,493,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Net Actuarial Loss	47,437,000	42,190,000
Amount Recognized in Accumulated Other Comprehensive Loss	47,437,000	42,190,000	34,396,000
Projected benefit obligation	218,400,000	199,300,000
Accumulated benefit obligation	207,800,000	188,100,000
Pension Benefits | Amounts Related to Unconsolidated Affiliate
Change in Plan Assets:
Funded Status at End of Year	(495,000)	(2,000)
Other Postretirement Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	73,659,000	69,511,000
Service Cost	681,000	533,000	945,000
Interest Cost	2,367,000	2,884,000	2,430,000
Actuarial Loss	3,933,000	5,228,000
Retiree Contributions	84,000	59,000
Plan Amendments	(753,000)	0
Benefits Paid	(4,431,000)	(4,556,000)
Settlement	0	0
Benefit Obligation at End of Year	75,540,000	73,659,000	69,511,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	82,522,000	70,531,000
Actual Return on Plan Assets	5,348,000	11,990,000
Employer Contributions	4,347,000	4,498,000
Retiree Contributions	84,000	59,000
Benefits Paid	(4,431,000)	(4,556,000)
Settlement	0	0
Fair Value of Plan Assets at End of Year	87,870,000	82,522,000	70,531,000
Funded Status at End of Year	12,330,000	8,863,000
Accrued Net Benefit (Cost) Credit at End of Year	12,629,000	9,096,000
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	12,629,000	9,096,000
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	(5,225,000)	(5,290,000)
Net Actuarial Loss	18,588,000	17,541,000
Amount Recognized in Regulatory Assets	13,363,000	12,251,000	15,219,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs (Credits)	(1,829,000)	(1,619,000)
Net Actuarial Loss	4,597,000	2,583,000
Amount Recognized in Accumulated Other Comprehensive Loss	2,768,000	964,000	687,000
Other Postretirement Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	47,306,000	44,882,000
Service Cost	396,000	343,000	583,000
Interest Cost	1,463,000	1,863,000	1,698,000
Actuarial Loss	(167,000)	3,481,000
Retiree Contributions	13,000	6,000
Plan Amendments	(436,000)	0
Benefits Paid	(2,386,000)	(3,269,000)
Benefit Obligation at End of Year	46,189,000	47,306,000	44,882,000
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	59,190,000	49,770,000
Actual Return on Plan Assets	2,679,000	9,419,000
Employer Contributions	2,373,000	3,264,000
Retiree Contributions	13,000	6,000
Benefits Paid	(2,386,000)	(3,269,000)
Fair Value of Plan Assets at End of Year	61,869,000	59,190,000	49,770,000
Funded Status at End of Year	15,680,000	11,884,000
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	15,680,000	11,884,000
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	(5,225,000)	(5,290,000)
Net Actuarial Loss	16,975,000	16,632,000
Amount Recognized in Regulatory Assets	11,750,000	11,342,000	14,628,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Net Actuarial Loss	0	0
Amount Recognized in Accumulated Other Comprehensive Loss	0	0	0
Other Postretirement Benefits | Amounts Related to Unconsolidated Affiliate
Change in Plan Assets:
Funded Status at End of Year	299,000	233,000
Supplemental Employee Retirement Plan
Change in Plan Assets:
Employer Contributions	3,900,000	4,100,000	2,700,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	93,600,000	84,500,000
Accumulated benefit obligation	90,600,000	80,500,000
Supplemental Employee Retirement Plan | South Jersey Gas Company
Change in Benefit Obligations:
Retiree Contributions	3,938,000	3,541,000	$ 3,861,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	93,200,000	84,100,000
Accumulated benefit obligation	$ 90,200,000	$ 80,100,000