PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 3,041,000	$ 3,341,000	$ 9,219,000	$ 10,151,000
Contributions			0	0
Estimated future contributions	0		0
Pension Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	1,900,000	2,300,000	6,300,000	6,700,000
Contributions			0	0
Estimated future contributions	0		0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(141,000)	(85,000)	(421,000)	(172,000)
Other Postretirement Benefits | SJG
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	(100,000)	$ (500,000)	(300,000)	$ (500,000)
Supplemental executive retirement plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated future contributions	$ 3,300,000		$ 3,300,000