REGULATORY ASSETS AND REGULATORY LIABILITIES - Regulatory Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
SJG
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 272,531	$ 286,539
SJG | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	17,088	20,805
SJG | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	252,499	259,863
SJG | Deferred Revenue - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
SJG | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,944	5,871
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	442,164	478,499
SJI | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	53,268	70,107
SJI | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	372,191	379,851
SJI | Deferred Revenue - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		3,188
SJI | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,944	5,871
SJI | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,646
SJI | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	11,687	17,039
SJI | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	415	2,443
ETG Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	166,981	189,336
ETG Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	34,761	47,909
ETG Utility Operations | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	118,459	118,757
ETG Utility Operations | Deferred Revenue - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		3,188
ETG Utility Operations | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
ETG Utility Operations | Weather Normalization
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,646
ETG Utility Operations | Amounts to be Refunded to Customers
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	11,687	17,039
ETG Utility Operations | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	415	2,443
ELK Utility Operations
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,652	2,624
ELK Utility Operations | Excess Plant Removal Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,419	1,393
ELK Utility Operations | Excess Deferred Taxes
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,233	1,231
ELK Utility Operations | Deferred Revenue - Net
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities		0
ELK Utility Operations | CIP Payable
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	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