COMMITMENTS AND CONTINGENT LIABILITIES - SCHEDULE OF FUTURE COMMITTED EXPENSES (Details) $ in Thousands	12 Months Ended
Sep. 30, 2018 USD ($)
Long-term Purchase Commitment [Line Items]
Current charges recoverable through BGSS	$ 112,000
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	689,609
2020	256,336
2021	189,877
2022	171,479
2023	152,560
Thereafter	$ 634,236
Minimum
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, fixed period	1 year
Maximum
Long-term Purchase Commitment [Line Items]
Storage and pipeline capacity, fixed period	10 years
Energy Services
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	$ 511,879
2020	98,105
2021	52,652
2022	33,057
2023	23,200
Thereafter	6,142
Energy Services \| Natural gas purchases
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	428,015
2020	28,389
2021	10,965
2022	0
2023	0
Thereafter	0
Energy Services \| Storage demand fees
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	31,716
2020	19,926
2021	13,478
2022	8,904
2023	4,212
Thereafter	991
Energy Services \| Pipeline demand fees
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	52,148
2020	49,790
2021	28,209
2022	24,153
2023	18,988
Thereafter	5,151
Natural Gas Distribution
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	177,730
2020	158,231
2021	137,225
2022	138,422
2023	129,360
Thereafter	628,094
Natural Gas Distribution \| Natural gas purchases
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	65,737
2020	37,727
2021	33,738
2022	33,546
2023	34,221
Thereafter	35,762
Natural Gas Distribution \| Storage demand fees
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	31,384
2020	24,263
2021	14,251
2022	12,930
2023	7,899
Thereafter	6,066
Natural Gas Distribution \| Pipeline demand fees
Purchase Obligation, Fiscal Year Maturity [Abstract]
2019	80,609
2020	96,241
2021	89,236
2022	91,946
2023	87,240
Thereafter	$ 586,266

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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