SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) county mi shares	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) shares
Accounting Policies [Abstract]
Number of counties in which SJG operates | county	7
Length of pipeline (in miles) | mi	118
Public utility assessment	$ 400,000	$ 400,000
Amount of costs related to interests in proved and unproved properties in Pennsylvania, net of amortization	$ 8,600,000		$ 8,700,000
Shares of treasury stock held (in shares) | shares	219,136		216,642
Goodwill	$ 3,578,000		$ 3,578,000
Public Utilities, General Disclosures [Line Items]
Nonoperating income	(2,761,000)	(4,487,000)
Costs and expenses	(364,075,000)	(356,965,000)
Impairment charge	0	0
Identified impairments	0	0
South Jersey Gas Company
Public Utilities, General Disclosures [Line Items]
Nonoperating income	(2,510,000)	(1,042,000)
Costs and expenses	(141,658,000)	(115,589,000)
Impairment charge	0	300,000
Accounting Standards Update 2017-07
Public Utilities, General Disclosures [Line Items]
Nonoperating income	1,200,000
Accounting Standards Update 2017-07 | South Jersey Gas Company
Public Utilities, General Disclosures [Line Items]
Costs and expenses	600,000
Corporate and Services | Sales Revenue, Net | Accounting Standards Update 2017-07
Public Utilities, General Disclosures [Line Items]
Prior period reclassification adjustment		$ 600,000
Gas Utility Operations | Operating Segments | Sales Revenue, Net | Accounting Standards Update 2017-07
Public Utilities, General Disclosures [Line Items]
Prior period reclassification adjustment	$ 600,000