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Financial Instruments Balance Sheet Location (Details) - USD ($) $ in Thousands | Mar. 31, 2018 | Sep. 30, 2017
--- | --- | ---
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | $ 602 | $ 3,239
Derivative Asset, Contract Netting | 0 | 0
Derivative Asset, Net of Contract Netting | 602 | 3,239
Derivative, Collateral, Right to Reclaim Cash | 0 | 0
Derivative Asset | 602 | 3,239
Derivative Liability, Fair Value, Gross Liability | (86,944) | (112,398)
Derivative Liability, Contract Netting | 0 | 0
Derivative Liability, Net of Contract Netting | (86,944) | (112,398)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset | 0 | 0
Derivative Liability | (86,944) | (112,398)
Designated As Hedging Instrument [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 0 | 0
Derivative Liability, Fair Value, Gross Liability | (85,948) | (112,076)
Designated As Hedging Instrument [Member] | Other Current Assets [Member] | Interest Rate Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 0 |
Designated As Hedging Instrument [Member] | Deferred Charges and Other Assets [Member] | Interest Rate Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset |  | 0
Designated As Hedging Instrument [Member] | Other Current Liabilities [Member] | Interest Rate Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability | (85,948) |
Designated As Hedging Instrument [Member] | Deferred Credits and Other Liabilities [Member] | Interest Rate Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability |  | (112,076)
Nondesignated [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 602 | 3,239
Derivative Liability, Fair Value, Gross Liability | (996) | (322)
Nondesignated [Member] | Other Current Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 602 | 2,436
Nondesignated [Member] | Deferred Charges and Other Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset |  | 803
Nondesignated [Member] | Other Current Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability | $ (996) | (322)
Nondesignated [Member] | Deferred Credits and Other Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability |  | $ 0

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