LINES OF CREDIT (Details)	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)
Line of Credit
Line of Credit Facility [Line Items]
Total Facility	$ 660,000,000
Usage	306,900,000
Available Liquidity	$ 353,100,000
Weighted average interest rate on borrowings	2.21%	1.43%
Average borrowings outstanding	$ 272,400,000	$ 325,500,000
Maximum amounts outstanding	$ 354,100,000	$ 467,700,000
Financial covenant, ratio of indebtedness to consolidated total capitalization (not more than)	0.65
Line of Credit | SJI
Line of Credit Facility [Line Items]
Total Facility	$ 450,000,000
Usage	303,300,000
Available Liquidity	146,700,000
Line of Credit | SJI | Revolving Credit Facilities
Line of Credit Facility [Line Items]
Total Facility	450,000,000
Usage	303,300,000
Available Liquidity	146,700,000
Letters of credit outstanding	9,800,000
Line of Credit | South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility	210,000,000
Usage	3,600,000
Available Liquidity	$ 206,400,000
Weighted average interest rate on borrowings	1.36%	0.67%
Average borrowings outstanding	$ 20,200,000	$ 73,700,000
Maximum amounts outstanding	110,100,000	$ 141,700,000
Line of Credit | South Jersey Gas Company | Revolving Credit Facilities
Line of Credit Facility [Line Items]
Total Facility	200,000,000
Usage	3,600,000
Available Liquidity	196,400,000
Letters of credit outstanding	800,000
Line of Credit | South Jersey Gas Company | Uncommitted Bank Line
Line of Credit Facility [Line Items]
Total Facility	10,000,000
Usage	0
Available Liquidity	10,000,000
Unsecured promissory notes | SJG Commercial Paper Program
Line of Credit Facility [Line Items]
Total Facility	$ 200,000,000
Fixed maturities of notes, at maximum number of days	270 days