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CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (Parenthetical) $ in Millions | 9 Months Ended
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Jun. 30, 2020 USD ($)
Statement of Cash Flows [Abstract] |
Cash acquired from asset acquisition | $ 5.1

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

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