DERIVATIVE INSTRUMENTS - INCOME STATEMENT RELATED DISCLOSURES (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Foreign Currency Contracts [Member] \| Gas Purchases [Member] \| Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (64)	$ (24)
Amount of Gain or (Loss) Reclassified from OCI into Income (Effective Portion)	12	(25)
Amount of Gain or (Loss) Recognized on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0
NJRES [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	31,913	113,956
NJRES [Member] \| Not Designated as Hedging Instrument [Member] \| Physical Commodity Contracts [Member] \| Operating Revenues [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	11,874	16,091
NJRES [Member] \| Not Designated as Hedging Instrument [Member] \| Physical Commodity Contracts [Member] \| Gas Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	(21,237)	(19,856)
NJRES [Member] \| Not Designated as Hedging Instrument [Member] \| Financial Commodity Contracts [Member] \| Gas Purchases [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized in income on derivatives	41,276	117,721
NJNG [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in regulatory assets and liabilities net	(5,600)	$ (19,000)
NJNG [Member] \| Treasury Lock [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in regulatory assets and liabilities net	$ 2,400

Net gain or loss on derivative instruments at NJNG that is deferred and recognized in regulatory assets and liabilities

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- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

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+ References

No definition available.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624177-113959

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- Definition

The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1),(2)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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