COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) $ in Thousands	9 Months Ended
Jun. 30, 2017 USD ($)
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 20,000
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	177,637
2018	337,024
2019	249,928
2020	142,629
2021	119,546
Thereafter	775,339
NJRES
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	138,801
2018	227,457
2019	116,156
2020	26,045
2021	20,125
Thereafter	28,225
NJRES \| Natural gas purchases
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	109,344
2018	146,646
2019	73,281
2020	1,298
2021	0
Thereafter	0
NJRES \| Storage demand fees
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	10,276
2018	32,262
2019	21,967
2020	12,913
2021	8,822
Thereafter	8,579
NJRES \| Pipeline demand fees
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	19,181
2018	48,549
2019	20,908
2020	11,834
2021	11,303
Thereafter	$ 19,646
NJRES \| Minimum
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	1 year
NJRES \| Maximum
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, contract term	10 years
NJNG
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	$ 38,836
2018	109,567
2019	133,772
2020	116,584
2021	99,421
Thereafter	747,114
NJNG \| Natural gas purchases
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	18,607
2018	9,972
2019	0
2020	0
2021	0
Thereafter	0
NJNG \| Storage demand fees
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	7,499
2018	30,042
2019	26,628
2020	15,332
2021	8,231
Thereafter	11,705
NJNG \| Pipeline demand fees
Natural Gas Purchases and Future Demand Fees, Next Five Fiscal Years
2017	12,730
2018	69,553
2019	107,144
2020	101,252
2021	91,190
Thereafter	$ 735,409

Current Charges Recoverable Through Basic Gas Supply Service as shown for the reporting period

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Storage and Pipeline Capacity, Term of Contract

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Minimum amount of purchase arrangement maturing after the fifth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the fourth fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the next fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the second fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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Minimum amount of purchase arrangement maturing in the third fiscal year following the latest fiscal year. Includes, but not limited to, recorded and unrecorded purchase obligations, long-term purchase commitments, and short-term purchase commitments.

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