PENSION AND OTHER POSTRETIREMENT BENEFITS - RECONCILIATIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	$ (3,727)	$ (3,631)
Noncurrent Liabilities	(114,055)	(110,112)
South Jersey Gas Company
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,693)	(3,597)
Noncurrent Liabilities	(99,981)	(96,053)
Pension Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	402,156	316,289
Acquisition Opening Obligation	0	100,362
Service Cost	5,583	6,442	$ 4,989
Interest Cost	17,294	13,778	11,772
Actuarial Loss (Gain)	44,047	(26,274)
Retiree Contributions	0	0
Plan Amendments	955	7,394
Benefits Paid	(30,662)	(15,835)
Benefit Obligation at End of Year	439,373	402,156	316,289
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	287,220	216,065
Acquisition Beginning Fair Value	0	94,685
Actual Return on Plan Assets	51,812	(10,399)
Employer Contributions	4,127	2,704
Retiree Contributions	0	0
Benefits Paid	(30,662)	(15,835)
Fair Value of Plan Assets at End of Year	312,497	287,220	216,065
Funded Status at End of Year	(126,876)	(114,936)
Accrued Net Benefit (Cost) Credit at End of Year	(126,878)	(115,083)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,727)	(3,631)
Noncurrent Liabilities	(123,151)	(111,452)
Net Amount Recognized at End of Year	(126,878)	(115,083)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	292	162
Net Actuarial Loss	61,292	67,377
Amount Recognized in Regulatory Assets	61,584	67,539	64,969
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs (Credits)	32	268
Net Actuarial Loss	51,253	42,257
Amount Recognized in Accumulated Other Comprehensive Loss	51,285	42,525	53,932
Projected benefit obligation	354,900	329,200
Accumulated benefit obligation	335,600	309,400
Pension Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	264,823	269,066
Service Cost	3,621	5,073	4,303
Interest Cost	11,067	10,010	9,925
Actuarial Loss (Gain)	24,020	(13,009)
Retiree Contributions	0	0
Plan Amendments	0	4,169
Benefits Paid	(17,014)	(10,486)
Benefit Obligation at End of Year	286,517	264,823	269,066
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	160,285	174,277
Actual Return on Plan Assets	23,760	(6,175)
Employer Contributions	3,927	2,669
Retiree Contributions	0	0
Benefits Paid	(17,013)	(10,486)
Fair Value of Plan Assets at End of Year	170,959	160,285	174,277
Funded Status at End of Year	(115,558)	(104,538)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(3,693)	(3,597)
Noncurrent Liabilities	(111,865)	(100,941)
Net Amount Recognized at End of Year	(115,558)	(104,538)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	292	163
Net Actuarial Loss	60,376	65,330
Amount Recognized in Regulatory Assets	60,668	65,493	64,969
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Net Actuarial Loss	42,190	34,396
Amount Recognized in Accumulated Other Comprehensive Loss	42,190	34,396	39,356
Projected benefit obligation	199,300	188,100
Accumulated benefit obligation	188,100	176,800
Pension Benefits | Amounts Related to Unconsolidated Affiliate
Change in Plan Assets:
Funded Status at End of Year	(2)	(147)
Other Postretirement Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	69,511	62,283
Acquisition Opening Obligation	0	13,195
Service Cost	533	945	910
Interest Cost	2,884	2,430	2,418
Actuarial Loss (Gain)	5,228	(3,534)
Retiree Contributions	59	265
Plan Amendments	0	(3,012)
Benefits Paid	(4,556)	(3,061)
Benefit Obligation at End of Year	73,659	69,511	62,283
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	70,531	57,922
Acquisition Beginning Fair Value	0	15,659
Actual Return on Plan Assets	11,990	(3,050)
Employer Contributions	4,498	2,796
Retiree Contributions	59	265
Benefits Paid	(4,556)	(3,061)
Fair Value of Plan Assets at End of Year	82,522	70,531	57,922
Funded Status at End of Year	8,863	1,020
Accrued Net Benefit (Cost) Credit at End of Year	9,096	1,340
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	9,096	1,340
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	(5,290)	(5,765)
Net Actuarial Loss	17,541	20,984
Amount Recognized in Regulatory Assets	12,251	15,219	13,242
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs (Credits)	(1,619)	(1,707)
Net Actuarial Loss	2,583	2,394
Amount Recognized in Accumulated Other Comprehensive Loss	964	687	3,506
Other Postretirement Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	44,882	49,098
Service Cost	343	583	582
Interest Cost	1,863	1,698	1,897
Actuarial Loss (Gain)	3,481	(1,271)
Retiree Contributions	6	143
Plan Amendments	0	(3,247)
Benefits Paid	(3,269)	(2,122)
Benefit Obligation at End of Year	47,306	44,882	49,098
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	49,770	52,663
Actual Return on Plan Assets	9,419	(2,893)
Employer Contributions	3,264	1,979
Retiree Contributions	6	143
Benefits Paid	(3,269)	(2,122)
Fair Value of Plan Assets at End of Year	59,190	49,770	52,663
Funded Status at End of Year	11,884	4,888
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	11,884	4,888
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs (Credits)	(5,290)	(5,765)
Net Actuarial Loss	16,632	20,393
Amount Recognized in Regulatory Assets	11,342	14,628	13,242
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	233	320
Supplemental Employee Retirement Plan
Change in Plan Assets:
Employer Contributions	4,100	2,700	2,400
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	84,500	73,000
Accumulated benefit obligation	80,500	69,500
Supplemental Employee Retirement Plan | South Jersey Gas Company
Change in Benefit Obligations:
Retiree Contributions	3,541	3,861	$ 2,235
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	84,100	72,600
Accumulated benefit obligation	$ 80,100	$ 69,100