REGULATORY ASSETS AND REGULATORY LIABILITIES - Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
SJG
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 225,409	$ 245,360
SJG | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	11,821	12,666
SJG | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	213,588	232,694
SJG | Deferred Gas Costs - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
SJG | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
SJG | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
SJI
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	404,826	420,577
SJI | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	45,685	50,619
SJI | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	326,033	346,582
SJI | Deferred Gas Costs - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	27,550	15,322
SJI | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	4,250	6,969
SJI | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,308	1,085
ETG Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	179,417	175,217
ETG Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	33,864	37,953
ETG Utility Operations | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	112,445	113,888
ETG Utility Operations | Deferred Gas Costs - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	27,550	15,322
ETG Utility Operations | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	4,250	6,969
ETG Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 1,308	$ 1,085