SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2017 USD ($) county mi shares	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) county mi shares	Sep. 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	$ 800,000	$ 700,000
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	213,061			213,061		212,617
Goodwill	$ 4,838,000			$ 4,838,000		$ 4,838,000
Public Utilities, General Disclosures [Line Items]
Cash Flows Provided by Operating Activities				127,081,000	196,433,000
Net Cash Flows from Financing Activities				89,752,000	(14,290,000)
Impairment charge	43,900,000	$ 300,000	0	44,200,000	0
Identified impairments	$ 0		0	0	0
South Jersey Gas Company
Public Utilities, General Disclosures [Line Items]
Cash Flows Provided by Operating Activities				73,186,000	108,690,000
Net Cash Flows from Financing Activities				114,670,000	45,593,000
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)