PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 2,212,000	$ 2,740,000	$ 4,424,000	$ 5,480,000
Contributions			0	0
Pension Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 1,500,000	$ 1,900,000	$ 3,100,000	$ 3,700,000
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
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ (632,000)	$ (524,000)	(1,264,000)	(1,049,000)
Other Postretirement Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost	$ 500,000	$ 700,000	$ 1,000,000.0	$ 1,400,000
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