REGULATORY ASSETS AND REGULATORY LIABILITIES - Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
SJG
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 473,402	$ 495,084
SJG | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	149,979	157,340
SJG | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	98,579	101,243
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	43,704	42,365
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	77,426	77,426
SJG | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	19,198	19,178
SJG | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	10,028	21,013
SJG | SBC Receivable (excluding RAC)
Regulatory Assets [Line Items]
Total Regulatory Assets	4,771	3,453
SJG | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	7,441	9,938
SJG | EET/EEP
Regulatory Assets [Line Items]
Total Regulatory Assets	16,848	18,725
SJG | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	411	434
SJG | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	5,981	6,091
SJG | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	11,883	11,822
SJG | WNC
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
SJG | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	27,153	26,056
SJI
Regulatory Assets [Line Items]
Total Regulatory Assets	650,710	673,992
SJI | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	156,013	162,536
SJI | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	187,284	193,080
SJI | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	(6,807)	(6,807)
SJI | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	71,298	67,818
SJI | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	33,316	33,898
SJI | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	85,892	85,892
SJI | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	19,198	19,178
SJI | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	10,028	21,013
SJI | SBC Receivable (excluding RAC)
Regulatory Assets [Line Items]
Total Regulatory Assets	4,771	3,453
SJI | Deferred Interest Rate Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	7,441	9,938
SJI | EET/EEP
Regulatory Assets [Line Items]
Total Regulatory Assets	19,757	21,787
SJI | Pipeline Supplier Service Charges
Regulatory Assets [Line Items]
Total Regulatory Assets	411	434
SJI | Pipeline Integrity Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	5,981	6,091
SJI | AFUDC - Equity Related Deferrals
Regulatory Assets [Line Items]
Total Regulatory Assets	11,883	11,822
SJI | WNC
Regulatory Assets [Line Items]
Total Regulatory Assets	6,120	7,444
SJI | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	38,124	36,415
ETG Utility Operations
Regulatory Assets [Line Items]
Total Regulatory Assets	177,308	178,908
ETG Utility Operations | Environmental Remediation Costs: Expended - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	6,034	5,196
ETG Utility Operations | Environmental Remediation Costs: Liability for Future Expenditures
Regulatory Assets [Line Items]
Total Regulatory Assets	88,705	91,837
ETG Utility Operations | Environmental Remediation Costs: Insurance Recovery Receivables
Regulatory Assets [Line Items]
Total Regulatory Assets	(6,807)	(6,807)
ETG Utility Operations | Deferred ARO Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	27,594	25,453
ETG Utility Operations | Deferred Pension Costs - Unrecognized Prior Service Cost
Regulatory Assets [Line Items]
Total Regulatory Assets	33,316	33,898
ETG Utility Operations | Deferred Pension and Other Postretirement Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	8,466	8,466
ETG Utility Operations | Deferred Gas Costs - Net
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | CIP Receivable
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
ETG Utility Operations | SBC Receivable (excluding RAC)
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/EEP
Regulatory Assets [Line Items]
Total Regulatory Assets	2,909	3,062
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 | WNC
Regulatory Assets [Line Items]
Total Regulatory Assets	6,120	7,444
ETG Utility Operations | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 10,971	$ 10,359