REGULATORY ASSETS AND REGULATORY LIABILITIES - Narrative and Regulatory Liabilities (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) site asset	Dec. 31, 2018 USD ($)
Environmental restoration costs
Regulatory Assets [Line Items]
Number of regulatory assets | asset	2
Original recovery period of expenditures	7 years
SJG Utility Operations
Regulatory Assets [Line Items]
Regulatory assets	$ 454,542	$ 492,365
Unprotected amount of excess deferred taxes	278,827	286,539
SJG Utility Operations | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Regulatory assets	$ 79,466	80,121
SJG Utility Operations | Environmental restoration costs
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	12
SJG Utility Operations | Weather Normalization
Regulatory Assets [Line Items]
Regulatory assets	$ 0	0
Unprotected amount of excess deferred taxes	0
SJG Utility Operations | Deferred Revenues - Net
Regulatory Assets [Line Items]
Increase in regulatory assets		34,300
SJG Utility Operations | Unprotected Excess Deferred Income Tax
Regulatory Assets [Line Items]
Unprotected amount of excess deferred taxes	$ 26,100
Period to refund to customers	5 years
South Jersey Industries Inc
Regulatory Assets [Line Items]
Regulatory assets	$ 624,187	662,969
Unprotected amount of excess deferred taxes	478,592	478,499
South Jersey Industries Inc | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Regulatory assets	82,103	82,758
South Jersey Industries Inc | Weather Normalization
Regulatory Assets [Line Items]
Regulatory assets	36	3,349
Unprotected amount of excess deferred taxes	1,400
South Jersey Industries Inc | Deferred Revenues - Net
Regulatory Assets [Line Items]
Increase in regulatory assets		(34,500)
Elizabethtown Gas
Regulatory Assets [Line Items]
Regulatory assets	169,251	169,921
Unprotected amount of excess deferred taxes	197,139	189,336
Elizabethtown Gas | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Regulatory assets	$ 2,607	2,607
Elizabethtown Gas | Environmental restoration costs
Regulatory Assets [Line Items]
Number of sites for environmental cleanup | site	6
Elizabethtown Gas | Weather Normalization
Regulatory Assets [Line Items]
Regulatory assets	$ 0	3,210
Unprotected amount of excess deferred taxes	$ 1,400	$ 3,200