PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	$ 1,940,000	$ 3,041,000	$ 7,420,000	$ 9,219,000
Contributions			0	0
Expected future employer contributions	0		0
Pension Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	$ 1,600,000	$ 1,900,000	$ 5,400,000	$ 6,300,000
Weighted average expected long term rate of return on plan assets (as a percent)	7.25%	7.25%	7.25%	7.25%
Contributions			$ 0	$ 0
Expected future employer contributions	$ 0		0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	(528,000)	$ (141,000)	(1,578,000)	(421,000)
Other Postretirement Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	$ (100,000)	$ (100,000)	$ (1,500,000)	$ (300,000)
Weighted average expected long term rate of return on plan assets (as a percent)	6.75%	6.75%	6.75%	6.75%
Supplemental executive retirement plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected future employer contributions	$ 3,700,000		$ 3,700,000