FAIR VALUE - DEBT (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Finance leases	$ 69,500	$ 74,200
NJR
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt issuance costs	3,400	3,400
Natural Gas Distribution
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt issuance costs	9,600	9,200
Fair market value \| Clean Energy Ventures \| Solar Asset Financing
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	162,000	149,200
Level 2 \| Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	2,102,845	2,102,845
Level 2 \| Fair market value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, fair value	$ 2,455,242	$ 2,417,748

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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