LINES OF CREDIT (Details)	3 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Line of Credit
Line of Credit Facility [Line Items]
Total Facility	$ 660,000,000
Usage	255,000,000
Available Liquidity	$ 405,000,000
Weighted average interest rate on borrowings	2.67%	1.98%
Average borrowings outstanding	$ 238,000,000	$ 287,900,000
Maximum amounts outstanding	$ 431,000,000	$ 354,100,000
Financial covenant, ratio of indebtedness to consolidated total capitalization, syndicate (not more than)	0.70
Line of Credit | SJI
Line of Credit Facility [Line Items]
Total Facility	$ 450,000,000
Usage	191,000,000
Available Liquidity	259,000,000
Line of Credit | SJI | Line of Credit
Line of Credit Facility [Line Items]
Total Facility	400,000,000
Usage	141,000,000
Available Liquidity	259,000,000
Letters of credit outstanding	6,000,000
Line of Credit | SJI | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	50,000,000
Usage	50,000,000
Available Liquidity	0
Line of Credit | South Jersey Gas Company
Line of Credit Facility [Line Items]
Total Facility	210,000,000
Usage	64,000,000
Available Liquidity	$ 146,000,000
Weighted average interest rate on borrowings	2.32%	1.15%
Average borrowings outstanding	$ 47,700,000	$ 34,700,000
Maximum amounts outstanding	$ 85,000,000	$ 110,100,000
Financial covenant, ratio of indebtedness to consolidated total capitalization (not more than)	0.65
Line of Credit | South Jersey Gas Company | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	$ 200,000,000
Usage	64,000,000
Available Liquidity	136,000,000
Letters of credit outstanding	900,000
Line of Credit | South Jersey Gas Company | Uncommitted Bank Line
Line of Credit Facility [Line Items]
Total Facility	10,000,000
Usage
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