PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	$ 2,740,000	$ 3,218,000
Contributions	0	0
Expected future employer contributions	0
Pension Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	1,900,000	2,300,000
Contributions	0	0
Expected future employer contributions	0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	(525,000)	(167,000)
Other Postretirement Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	700,000	$ (100,000)
Supplemental executive retirement plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected future employer contributions	$ 3,700,000