LINES OF CREDIT (Details)	1 Months Ended		12 Months Ended
	Sep. 30, 2017	Aug. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Line of Credit Facility [Line Items]
Total Facility			$ 660,000,000
Usage			353,800,000
Available Liquidity			$ 306,200,000
Weighted average borrowing cost			2.46%	1.47%	1.13%
Average borrowings outstanding			$ 276,700,000	$ 321,900,000
Maximum amounts outstanding			$ 373,800,000	$ 467,700,000
Financial covenant, ratio of indebtedness to consolidated total capitalization (not more than)			0.65
Letters of credit
Line of Credit Facility [Line Items]
Total Facility			$ 6,600,000.0
South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility			210,000,000
Usage			52,800,000
Available Liquidity			157,200,000
Letters of credit outstanding			$ 800,000
Weighted average interest rate			1.88%	0.97%	0.66%
Average borrowings outstanding			$ 17,600,000	$ 71,500,000
Maximum amounts outstanding			$ 110,100,000	$ 141,700,000
Financial covenant, ratio of indebtedness to consolidated total capitalization (not more than)			700.00
South Jersey Gas Company | Syndicated Revolving Credit Facility | Term facility
Line of Credit Facility [Line Items]
Total Facility		$ 200,000,000.0
South Jersey Gas Company | Syndicated Revolving Credit Facility | Term facility | August 2017 to August 2022
Line of Credit Facility [Line Items]
Total Facility		$ 200,000,000.0
Term of agreement		5 years
South Jersey Gas Company | Letters of credit
Line of Credit Facility [Line Items]
Letters of credit outstanding			$ 6,600,000
South Jersey Industries Inc.
Line of Credit Facility [Line Items]
Total Facility			450,000,000
Usage			301,000,000
Available Liquidity			149,000,000
South Jersey Industries Inc. | Term facility | Term facility
Line of Credit Facility [Line Items]
Total Facility		$ 400,000,000
South Jersey Industries Inc. | Term facility | Term facility | August 2017 to August 2022
Line of Credit Facility [Line Items]
Total Facility		$ 400,000,000.0
Term of agreement		5 years
South Jersey Industries Inc. | Syndicated Revolving Credit Facility | Term facility
Line of Credit Facility [Line Items]
Term of agreement	2 years
Term facility | South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility			10,000,000
Usage			0
Available Liquidity			10,000,000
Syndicated Revolving Credit Facility | South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility			200,000,000
Usage			52,800,000
Available Liquidity			147,200,000
Syndicated Revolving Credit Facility | South Jersey Industries Inc.
Line of Credit Facility [Line Items]
Total Facility			400,000,000
Usage			251,000,000
Available Liquidity			149,000,000
Revolving Credit Facility | South Jersey Industries Inc.
Line of Credit Facility [Line Items]
Total Facility			50,000,000
Usage			50,000,000
Available Liquidity			0
South Jersey Gas commercial paper program | South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility			$ 200,000,000.0
Fixed maturities of notes, which may not exceed specified number of days			270 days