AFFILIATIONS, DISCONTINUED OPERATIONS AND RELATED PARTY TRANSACTIONS - Related Party Transactions (Details) - SJG - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	$ 2,714	$ 1,066
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	7,625	6,719
SJRG
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	2,588	963
Costs of Sales/Affiliates (Excluding depreciation)	25,338	10,450
Marina
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	103	82
SJI
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	7,043	6,050
Millennium
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	697	708
Other
Operating Revenues/Affiliates:
Total Operating Revenue/Affiliates	23	21
Operations Expense/Affiliates:
Total Operations Expense/Affiliates	$ (115)	$ (39)