FAIR VALUE - DEBT (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total lease liability	$ 74,159	$ 35,400
NJNG
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt issuance costs	9,195	9,027
Fair market value \| Solar Asset Financing \| Clean Energy Ventures
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	149,200	98,600
NJR
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt issuance costs	3,400	2,000
Significant Other Observable Inputs (Level 2) \| NJNG \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	1,092,845	892,845
Significant Other Observable Inputs (Level 2) \| NJNG \| Fair market value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	1,271,715	984,129
Significant Other Observable Inputs (Level 2) \| NJR \| Carrying value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	1,010,000	550,000
Significant Other Observable Inputs (Level 2) \| NJR \| Fair market value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 1,146,033	$ 584,735

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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-Publisher FASB
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Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
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-Publisher FASB
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