PENSION AND OTHER POSTRETIREMENT BENEFITS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	$ 1,719,000	$ 2,177,000
Interest Cost	4,229,000	5,108,000
Expected Return on Plan Assets	(5,193,000)	(7,633,000)
Amortizations:
Prior Service Cost	26,000	71,000
Actuarial Loss	2,437,000	4,132,000
Net Periodic Benefit Cost	3,218,000	3,855,000
Capitalized Benefit Cost	(594,000)	(483,000)
Deferred Benefit Cost	(541,000)	(751,000)
Total Net Periodic Benefit Expense	2,083,000	2,621,000
Contributions	0
Estimated future contributions	0
Pension Benefits | SJG Utility Operations
Amortizations:
Net Periodic Benefit Cost	2,300,000	2,500,000
Estimated future contributions	0
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service Cost	234,000	81,000
Interest Cost	628,000	217,000
Expected Return on Plan Assets	(1,149,000)	(305,000)
Amortizations:
Prior Service Cost	(143,000)	(31,000)
Actuarial Loss	263,000	111,000
Net Periodic Benefit Cost	(167,000)	73,000
Capitalized Benefit Cost	(56,000)	(5,000)
Deferred Benefit Cost	116,000	0
Total Net Periodic Benefit Expense	(107,000)	68,000
Other Postretirement Benefits | SJG Utility Operations
Amortizations:
Net Periodic Benefit Cost		$ 100,000
Supplemental executive retirement plan
Amortizations:
Estimated future contributions	$ 3,600,000