RELATED PARTY TRANSACTIONS (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Related Party Transaction [Line Items]
Operating Revenues/Affiliates	$ 780		$ 174		$ 1,489		$ 459
Operations Expense/Affiliates	4,903		4,395		9,926		9,061
SJRG [Member]
Related Party Transaction [Line Items]
Operating Revenues/Affiliates	463		89		850		272
Costs of Sales/Affiliates (Excluding depreciation)	4,758		4,267		5,669		5,762
Energy-Related Derivative (Gains) / Losses	(1,278)	[1]	5,688	[1]	179	[1]	10,655	[1]
SJI [Member]
Related Party Transaction [Line Items]
Operations Expense/Affiliates	2,954		2,486		5,876		5,163
SJIS [Member]
Related Party Transaction [Line Items]
Operations Expense/Affiliates	1,379		1,255		2,934		2,593
Millennium [Member]
Related Party Transaction [Line Items]
Operations Expense/Affiliates	675		796		1,349		1,583
Other [Member]
Related Party Transaction [Line Items]
Operating Revenues/Affiliates	317		85		639		187
Operations Expense/Affiliates	$ (105)		$ (142)		$ (233)		$ (278)

[1] Contracts used to hedge natural gas purchases. Included in Cost of Sales on the Condensed Statement of Income.