LINES OF CREDIT AND SHORT-TERM - WEIGHTED AVERAGE INTEREST RATES, AVERAGE BORROWINGS, AND MAXIMUM AMOUNTS OUTSTANDING (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Maximum amounts outstanding	$ 872,200	$ 907,500
South Jersey Gas Company
Line of Credit Facility [Line Items]
Maximum amounts outstanding	$ 187,000	$ 196,500
Line of Credit
Line of Credit Facility [Line Items]
Weighted average interest rate on borrowings (as a percent)	1.35%	2.67%	3.32%
Average borrowings outstanding, not including LOC	$ 472,900	$ 560,200
Line of Credit | South Jersey Gas Company
Line of Credit Facility [Line Items]
Weighted average interest rate on borrowings (as a percent)	0.23%	1.99%	2.96%
Average borrowings outstanding, not including LOC	$ 116,600	$ 113,300