SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) county mi shares	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) county mi shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) shares
Accounting Policies [Abstract]
Number of counties in which SJG operates | county	7		7
Length of pipeline (in miles) | mi	118		118
Public utility assessment	$ 200,000	$ 200,000	$ 600,000	$ 500,000
Amount of costs related to interests in proved and unproved properties in Pennsylvania, net of amortization	$ 8,700,000		$ 8,700,000		$ 8,800,000
Shares of treasury stock held (in shares) | shares	211,217		211,217		212,617
Goodwill	$ 4,838,000		$ 4,838,000		$ 4,838,000
Public Utilities, General Disclosures [Line Items]
Cash Flows Provided by Operating Activities			123,658,000	158,099,000
Net Cash Flows from Financing Activities			19,313,000	(42,705,000)
Impairment charge	0	0	300,000	0
Identified impairments	$ 0	0	0	0
South Jersey Gas Company
Public Utilities, General Disclosures [Line Items]
Cash Flows Provided by Operating Activities			75,514,000	97,394,000
Net Cash Flows from Financing Activities			57,471,000	4,900,000
Impairment charge		$ 0	$ 0	0
Accounting Standards Update 2016-09, Statutory Tax Withholding Component
Public Utilities, General Disclosures [Line Items]
Cash Flows Provided by Operating Activities				400,000
Net Cash Flows from Financing Activities				$ (400,000)