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Financial Instruments Balance Sheet Location (Details) - USD ($) $ in Thousands | Jun. 30, 2017 | Sep. 30, 2016
--- | --- | ---
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | $ 3,228 | $ 44,141
Derivative Asset, Contract Netting | 0 | (39,290)
Derivative Asset, Net of Contract Netting | 3,228 | 4,851
Derivative, Collateral, Right to Reclaim Cash | 0 | 6,775
Derivative Asset | 3,228 | 11,626
Derivative Liability, Fair Value, Gross Liability | (109,372) | (323,684)
Derivative Liability, Contract Netting | 0 | (39,290)
Derivative Liability, Net of Contract Netting | (109,372) | (284,394)
Derivative Liability, Collateral, Right to Reclaim Cash, Offset | 0 | (43,575)
Derivative Liability | (109,372) | (240,819)
Designated As Hedging Instrument [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 0 | 8,790
Derivative Liability, Fair Value, Gross Liability | (108,860) | (292,171)
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] | Other Current Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset |  | 6,612
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 | 0
Designated As Hedging Instrument [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset |  | 2,178
Designated As Hedging Instrument [Member] | Other Current Liabilities [Member] | Interest Rate Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability |  | (68,481)
Designated As Hedging Instrument [Member] | Other Current Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability |  | (21,903)
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 | (108,860) | (198,008)
Designated As Hedging Instrument [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability |  | (3,779)
Nondesignated [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 3,228 | 35,351
Derivative Liability, Fair Value, Gross Liability | (512) | (31,513)
Nondesignated [Member] | Other Current Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 2,960 | 21,186
Nondesignated [Member] | Deferred Charges And Other Assets [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Asset, Fair Value, Gross Asset | 268 | 14,165
Nondesignated [Member] | Other Current Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability | (230) | (18,812)
Nondesignated [Member] | Deferred Credits And Other Liabilities [Member] | Commodity Contract [Member] |  |
Derivatives Fair Value [Line Items] |  |
Derivative Liability, Fair Value, Gross Liability | $ (282) | $ (12,701)

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