AFFILIATIONS, DISCONTINUED OPERATIONS AND RELATED PARTY TRANSACTIONS - Related Party Transactions (Details) - SJG - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	$ 803	$ 1,303	$ 4,738	$ 3,703
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	(6,786)	(4,860)	(21,746)	(17,238)
SJRG
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	691	1,210	4,388	3,421
Costs of Sales/Affiliates (Excluding depreciation and amortization)	1,094	1,453	28,525	12,399
Marina
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	89	72	281	219
SJI
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	(6,148)	(4,316)	(19,899)	(15,354)
Millennium
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	(750)	(717)	(2,191)	(2,137)
Other
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	23	21	69	63
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	$ 112	$ 173	$ 344	$ 253