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DEBT - NJR SHORT-TERM DEBT (Details) |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Dec. 14, 2017 USD ($) | Sep. 30, 2018 USD ($) debt_instrument Mutual_option | Apr. 18, 2018 USD ($) | Jan. 19, 2018 USD ($) | Sep. 30, 2017 USD ($)
Short-term Debt [Line Items] |  |  |  |  |  |
Number of mutual options | Mutual_option |  |  | 2 |  |  |
Number of mutual options, extension period |  |  | 1 year |  |  |
Letters of credit |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Letters of credit outstanding, amount |  |  |  |  |  | $ 13,400,000
Revolving line of credit, 4 months |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 75,000,000 |  |  |  |
Line of credit facility, maximum borrowing capacity, incremental increase |  |  |  |  | $ 100,000,000 |
Debt instrument, term |  | 4 months |  |  |  |
Line of credit facility, fair value of amount outstanding |  |  |  | $ 0 |  |
NJR | Letters of credit |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Number of debt instruments (in debt instruments) | debt_instrument |  |  | 6 |  |  |
Letters of credit outstanding, amount |  |  | $ 14,900,000 |  |  |
NJR | Letters of Credit on Behalf of NJRES |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Number of debt instruments (in debt instruments) | debt_instrument |  |  | 3 |  |  |
Letters of credit outstanding, amount |  |  | $ 11,900,000 |  |  |
NJR | Letters of Credit on Behalf of NJRCEV |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Number of debt instruments (in debt instruments) | debt_instrument |  |  | 3 |  |  |
Letters of credit outstanding, amount |  |  | $ 3,000,000 |  |  |
NJR | Committed Credit Facilities Due September 2020 |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] |  | 425,000,000 |  |  | $ 425,000,000
NJR | Bank revolving credit facilities |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity, incremental increase |  |  | 5,000,000 |  |  |
Line of credit facility, maximum borrowing capacity, maximum increase |  |  | $ 100,000,000 |  |  |
[1] | Committed credit facilities, which require commitment fees of .075 percent on the unused amounts.

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- Definition Line of Credit Facility, Maximum Borrowing Capacity, Incremental Increase + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Line of Credit Facility, Maximum Borrowing Capacity, Maximum Increase + References No definition available. + Details
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- Definition Number of Debt Instruments + References No definition available. + Details
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- Definition Number of Mutual Options + References No definition available. + Details
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- Definition Number of Mutual Options, Extension Period + References No definition available. + Details
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- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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- Definition Fair value of the amount outstanding under the credit facility. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
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