REGULATORY ASSETS AND REGULATORY LIABILITIES - Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
SJG
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 486,070	$ 496,177
SJG | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	160,828	156,279
SJG | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	102,889	131,262
SJG | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
SJG | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	40,858	36,515
SJG | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
SJG | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	72,010	72,010
SJG | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	19,222	49,469
SJG | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	16,242
SJG | SBC Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	2,665	1,478
SJG | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	10,872	7,856
SJG | EET
Regulatory Assets [Line Items]
Total Regulatory Assets	16,810	12,877
SJG | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	457	525
SJG | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	5,837	6,516
SJG | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	11,491	10,712
SJG | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
SJG | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	25,889	10,678
SJI
Regulatory Assets [Line Items]
Total Regulatory Assets	659,724	665,932
SJI | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	171,095	173,234
SJI | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	196,000	232,345
SJI | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	(13,615)	(20,423)
SJI | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	64,449	54,623
SJI | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	34,940	37,378
SJI | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	73,835	73,835
SJI | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	19,222	55,063
SJI | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	16,242
SJI | SBC Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	2,665	1,478
SJI | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	10,872	7,856
SJI | EET
Regulatory Assets [Line Items]
Total Regulatory Assets	16,810	12,877
SJI | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	457	525
SJI | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	5,837	6,516
SJI | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	11,491	10,712
SJI | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Assets	5,535	231
SJI | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	43,889	19,682
ETG Utility Operations
Regulatory Assets [Line Items]
Total Regulatory Assets	173,654	169,231
ETG Utility Operations | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	10,267	16,955
ETG Utility Operations | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	93,111	101,083
ETG Utility Operations | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	(13,615)	(20,423)
ETG Utility Operations | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	23,591	18,108
ETG Utility Operations | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	34,940	37,378
ETG Utility Operations | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,825	1,825
ETG Utility Operations | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	0	5,301
ETG Utility Operations | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	0
ETG Utility Operations | SBC Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | EET
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Assets	5,535	0
ETG Utility Operations | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	18,000	9,004
ELK Utility Operations
Regulatory Assets [Line Items]
Total Regulatory Assets	0	524
ELK Utility Operations | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	0	293
ELK Utility Operations | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	0
ELK Utility Operations | SBC Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | EET
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ELK Utility Operations | Weather Normalization
Regulatory Assets [Line Items]
Total Regulatory Assets	0	231
ELK Utility Operations | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 0	$ 0