AFFILIATIONS, DISCONTINUED OPERATIONS AND RELATED-PARTY TRANSACTIONS - RELATED PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
South Jersey Gas Company
Related Party Transaction [Line Items]
Total Operating Revenues/Affiliates	$ 4,858	$ 7,319	$ 5,944
Total Operations Expense/Affiliates	24,357	22,901	16,422
South Jersey Gas Company | SJRG
Related Party Transaction [Line Items]
Total Operating Revenues/Affiliates	4,458	6,934	5,342
Cost of Sales/Affiliates	24,337	16,306	26,090
Derivative Losses/(Gains)	0	0	64
South Jersey Gas Company | Marina
Related Party Transaction [Line Items]
Total Operating Revenues/Affiliates	314	302	185
South Jersey Gas Company | Other
Related Party Transaction [Line Items]
Total Operating Revenues/Affiliates	86	83	417
Total Operations Expense/Affiliates	(653)	(198)	(412)
South Jersey Gas Company | SJI
Related Party Transaction [Line Items]
Total Operations Expense/Affiliates	22,154	20,296	14,088
South Jersey Gas Company | Millennium
Related Party Transaction [Line Items]
Total Operations Expense/Affiliates	$ 2,856	2,803	$ 2,746
EnergyMark | South Jersey Energy Company
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage	33.00%
EnergyMark | SJRG
Related Party Transaction [Line Items]
Total Operating Revenues/Affiliates	$ 37,500	$ 31,400