PENSION AND OTHER POSTRETIREMENT BENEFITS - NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of employees entitled to annuity payments upon retirement	39.00%
Pension Benefits
Net periodic benefit cost [Abstract]
Service Cost	$ 4,989	$ 4,843	$ 5,337
Interest Cost	11,772	12,125	11,168
Expected Return on Plan Assets	(14,105)	(13,508)	(14,789)
Amortizations:
Prior Service (Credits) Cost	131	212	212
Actuarial Loss	10,282	9,394	10,608
Net Periodic Benefit Cost	13,069	13,066	12,536
Capitalized Benefit Costs	(4,723)	(4,645)	(4,805)
Affiliate SERP Allocations	0	0
Deferred Benefit Costs	(527)	(645)	(1,007)
Total Net Periodic Benefit Expense	7,819	7,776	6,724
Other Postretirement Benefits
Net periodic benefit cost [Abstract]
Service Cost	910	851	1,116
Interest Cost	2,418	2,615	2,973
Expected Return on Plan Assets	(3,411)	(3,104)	(2,993)
Amortizations:
Prior Service (Credits) Cost	(344)	(344)	608
Actuarial Loss	1,238	1,109	1,342
Net Periodic Benefit Cost	811	1,127	3,046
Capitalized Benefit Costs	(46)	(277)	(1,043)
Affiliate SERP Allocations	(19)	(81)
Curtailment Costs (Credit)	(106)	0	0
Deferred Benefit Costs	0	0	(256)
Total Net Periodic Benefit Expense	$ 659	850	1,747
South Jersey Gas Company
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Percentage of employees entitled to annuity payments upon retirement	56.00%
South Jersey Gas Company | Pension Benefits
Net periodic benefit cost [Abstract]
Service Cost	$ 4,303	4,144	4,430
Interest Cost	9,925	10,292	9,357
Expected Return on Plan Assets	(11,366)	(11,029)	(11,914)
Amortizations:
Prior Service (Credits) Cost	127	203	203
Actuarial Loss	8,692	7,975	8,969
Net Periodic Benefit Cost	11,681	11,585	11,045
Capitalized Benefit Costs	(4,723)	(4,645)	(4,805)
Affiliate SERP Allocations	0	0
Deferred Benefit Costs	(527)	(644)	(1,007)
Total Net Periodic Benefit Expense	4,196	4,336	3,545
South Jersey Gas Company | Supplemental Employee Retirement Plan
Amortizations:
Affiliate SERP Allocations	(2,235)	(1,960)	(1,688)
South Jersey Gas Company | Other Postretirement Benefits
Net periodic benefit cost [Abstract]
Service Cost	582	576	726
Interest Cost	1,897	2,120	2,406
Expected Return on Plan Assets	(3,101)	(2,823)	(2,708)
Amortizations:
Prior Service (Credits) Cost	(257)	(257)	499
Actuarial Loss	972	945	1,107
Net Periodic Benefit Cost	93	561	2,030
Capitalized Benefit Costs	(46)	(277)	(1,043)
Affiliate SERP Allocations	(15)	(70)
Deferred Benefit Costs	0	0	(256)
Total Net Periodic Benefit Expense	$ 47	$ 284	$ 731