PENSION AND OTHER POSTRETIREMENT BENEFITS - RECONCILIATIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	$ (2,388)	$ (2,463)
Noncurrent Liabilities	(101,544)	(95,235)
South Jersey Gas Company
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(2,353)	(2,428)
Noncurrent Liabilities	(88,871)	(81,800)
Pension Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	278,288	254,195
Service Cost	4,989	4,843	$ 5,337
Interest Cost	11,772	12,125	11,168
Actuarial Loss (Gain)	32,893	18,254
Retiree Contributions	0	0
Plan Amendments	0	0
Benefit Obligation at End of Year	316,289	278,288	254,195
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	189,542	184,824
Actual Return on Plan Assets	25,807	13,569
Employer Contributions	12,369	2,278
Retiree Contributions		0
Benefits Paid	(11,653)	(11,129)
Fair Value of Plan Assets at End of Year	216,065	189,542	184,824
Funded Status at End of Year	(100,224)	(88,746)
Accrued Net Benefit Cost at End of Year	(100,089)	(88,420)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(2,388)	(2,463)
Noncurrent Liabilities	(97,701)	(85,957)
Net Amount Recognized at End of Year	(100,089)	(88,420)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs	428	538
Net Actuarial Loss	64,541	67,912
Amount Recognized in Regulatory Assets	64,969	68,450	64,432
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs	47	69
Net Actuarial Loss	53,885	39,521
Amount Recognized in Accumulated Other Comprehensive Loss	53,932	39,590	35,066
Projected benefit obligation	243,900	224,300
Accumulated benefit obligation	227,300	208,300
Benefits Paid	(11,653)	(11,129)
Pension Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	236,356	213,660
Service Cost	4,303	4,144	4,430
Interest Cost	9,925	10,292	9,357
Actuarial Loss (Gain)	27,892	17,463
Retiree Contributions	0	0
Plan Amendments	0	0
Benefit Obligation at End of Year	269,066	236,356	213,660
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	154,729	149,032
Actual Return on Plan Assets	18,666	12,656
Employer Contributions	10,292	2,244
Retiree Contributions	0	0
Benefits Paid	(9,410)	(9,203)
Fair Value of Plan Assets at End of Year	174,277	154,729	149,032
Funded Status at End of Year	(94,789)	(81,627)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	(2,353)	(2,428)
Noncurrent Liabilities	(92,436)	(79,199)
Net Amount Recognized at End of Year	(94,789)	(81,627)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs	428	538
Net Actuarial Loss	64,541	67,912
Amount Recognized in Regulatory Assets	64,969	68,450	64,432
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Net Actuarial Loss	39,356	24,102
Amount Recognized in Accumulated Other Comprehensive Loss	39,356	24,102	20,463
Projected benefit obligation	197,000	183,200
Accumulated benefit obligation	183,500	170,000
Benefits Paid	(9,410)	(9,203)
Pension Benefits | Amounts Related to Unconsolidated Affiliate
Change in Plan Assets:
Funded Status at End of Year	135	326
Other Postretirement Benefits
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	60,350	57,430
Service Cost	910	851	1,116
Interest Cost	2,418	2,615	2,973
Actuarial Loss (Gain)	1,411	3,121
Retiree Contributions	19	81
Plan Amendments	0	0
Benefit Obligation at End of Year	62,283	60,350	57,430
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	50,532	47,759
Actual Return on Plan Assets	7,390	2,784
Employer Contributions	2,806	3,656
Retiree Contributions	19	81
Benefits Paid	(2,825)	(3,748)
Fair Value of Plan Assets at End of Year	57,922	50,532	47,759
Funded Status at End of Year	(4,361)	(9,818)
Accrued Net Benefit Cost at End of Year	(3,843)	(9,278)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	(3,843)	(9,278)
Net Amount Recognized at End of Year	(3,843)	(9,278)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs	(2,775)	(3,032)
Net Actuarial Loss	16,017	20,275
Amount Recognized in Regulatory Assets	13,242	17,243	15,347
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Prior Service Costs	(906)	(989)
Net Actuarial Loss	4,412	3,810
Amount Recognized in Accumulated Other Comprehensive Loss	3,506	2,821	2,062
Benefits Paid	(2,825)	(3,748)
Other Postretirement Benefits | South Jersey Gas Company
Change in Benefit Obligations:
Benefit Obligation at Beginning of Year	48,549	46,518
Service Cost	582	576	726
Interest Cost	1,897	2,120	2,406
Actuarial Loss (Gain)	328	2,292
Retiree Contributions	15	70
Plan Amendments	0	0
Benefit Obligation at End of Year	49,098	48,549	46,518
Change in Plan Assets:
Fair Value of Plan Assets at Beginning of Year	45,948	43,428
Actual Return on Plan Assets	6,715	2,531
Employer Contributions	2,259	2,946
Retiree Contributions	14	70
Benefits Paid	(2,273)	(3,027)
Fair Value of Plan Assets at End of Year	52,663	45,948	43,428
Funded Status at End of Year	3,565	(2,601)
Amounts Recognized in the Statement of Financial Position Consist of:
Current Liabilities	0	0
Noncurrent Liabilities	3,565	(2,601)
Net Amount Recognized at End of Year	3,565	(2,601)
Amounts Recognized in Regulatory Assets Consist of:
Prior Service Costs	(2,775)	(3,032)
Net Actuarial Loss	16,017	20,275
Amount Recognized in Regulatory Assets	13,242	17,243	15,347
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
Benefits Paid	(2,273)	(3,027)
Other Postretirement Benefits | Amounts Related to Unconsolidated Affiliate
Change in Plan Assets:
Funded Status at End of Year	518	540
Supplemental Employee Retirement Plan
Change in Plan Assets:
Employer Contributions	2,400	2,300	2,000
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	72,400	53,900
Accumulated benefit obligation	63,900	51,900
Supplemental Employee Retirement Plan | South Jersey Gas Company
Change in Benefit Obligations:
Retiree Contributions	2,235	1,960	$ 1,688
Amounts Recognized in Accumulated Other Comprehensive Loss Consist of (pre-tax):
Projected benefit obligation	72,000	53,200
Accumulated benefit obligation	$ 63,600	$ 51,200