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DEBT - FIRST MORTGAGE BONDS (Details) $ in Thousands |  | 12 Months Ended |  |
--- | --- | --- | --- | ---
Jan. 17, 2017 USD ($) | Sep. 30, 2017 USD ($) | Sep. 30, 2016 USD ($) | Sep. 30, 2015 USD ($) | Jun. 21, 2016 | Aug. 31, 2011 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |
NJBPU dividend restriction, equity to capitalization ratio |  | 0.3 |  |  |  |
Debt to equity ratio |  | 0.556 |  |  |  |
Payment of long-term debt |  | $ 97,854 | $ 13,289 | $ 37,039 |  |
Variable Rate Debt |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Long-term debt |  |  |  |  |  | $ 97,000
First mortgage bonds: |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Maximum amount that can be issued |  | 960,000 |  |  |  |
First mortgage bonds: | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Payment of long-term debt | $ 35,800 |  |  |  |  |
First mortgage bonds: | Series UU | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Long-term debt |  | $ 125,000 | 125,000 |  |  |
Stated interest rate |  | 3.63% |  |  | 3.63% |
First mortgage bonds: | Series II | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Long-term debt |  | $ 0 | $ 10,300 |  |  |
Stated interest rate |  | 4.50% |  |  |  |
Variable Demand Rate Notes | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Interest rate on EDA Bonds |  | 1.42% |  |  |  |
Minimum | First mortgage bonds: | Series II | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Stated interest rate | 4.50% |  |  |  |  |
Maximum | First mortgage bonds: | Series II | Natural Gas Distribution |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Stated interest rate | 4.90% |  |  |  |  |

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- Definition Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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