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CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Millions | 12 Months Ended
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Sep. 30, 2020 USD ($)
Statement of Cash Flows [Abstract] |
Cash acquired | $ 5.1

X
- Definition Cash Acquired From Asset Acquisition + References No definition available. + Details
Name: | njr_CashAcquiredFromAssetAcquisition
Namespace Prefix: | njr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_StatementOfCashFlowsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration