PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net Periodic Benefit Cost (Credit)	$ 2,740,000	$ 2,961,000	$ 5,480,000	$ 6,179,000
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)	$ 1,900,000	$ 2,100,000	$ 3,700,000	$ 4,400,000
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)	(524,000)	$ (114,000)	(1,049,000)	(281,000)
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)	$ (1,400,000)	$ (200,000)
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