REGULATORY ASSETS AND REGULATORY LIABILITIES - Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
SJG
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 255,229	$ 274,482
SJG | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	13,853	16,333
SJG | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	241,376	251,355
SJG | Deferred Revenues - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
SJG | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		6,794
SJG | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		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	434,148	442,918
SJI | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	52,700	52,676
SJI | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	357,167	369,050
SJI | Deferred Revenues - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	15,205	52
SJI | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		6,794
SJI | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		2,684
SJI | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,500	10,625
SJI | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	576	1,037
ETG Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	178,919	168,436
ETG Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	38,847	36,343
ETG Utility Operations | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	115,791	117,695
ETG Utility Operations | Deferred Revenues - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	15,205	52
ETG Utility Operations | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
ETG Utility Operations | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		2,684
ETG Utility Operations | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,500	10,625
ETG Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	576	1,037
ELK Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ELK Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ELK Utility Operations | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ELK Utility Operations | Deferred Revenues - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ELK Utility Operations | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
ELK Utility Operations | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
ELK Utility Operations | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ELK Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 0	$ 0