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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

NJBPU Dividend Restriction Equity to Capitalization Ratio

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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

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-SubTopic 210
-Section S99
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-Subparagraph (SX 210.7-03(a)(16))
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Indebtedness divided by net capital.

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The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

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