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v3.20.4

Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions, $ in Millions | 3 Months Ended |
--- | --- | ---
Dec. 31, 2020 USD ($) gal | Dec. 31, 2019 gal | Sep. 30, 2020 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Hedging positions and payable amounts secured under credit facility | $ | $ 1.8 |  | $ 11.1
Prepaid expense and other current assets |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Aggregated cash posted as collateral in normal course of business | $ | 2.5 |  |
Interest rate swap |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Notional Value | $ | $ 62.8 |  | 64.0
Percentage of market risk exposure of long term debt | 52.00% |  |
Fair Value | $ | $ (2.8) |  | $ (3.1)
Call Option |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 8.5 | 7.4 |
Call Option | Synthetic calls |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 86.5 | 85.8 |
Put Option |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 5.1 | 7.2 |
Swap Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 11.2 | 17.2 |
Swap Contracts Bought | Short |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 0.6 | 0.2 |
Future Contracts | Short |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 29.1 | 42.1 |
Future Contracts | Long |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 3.8 | 18.2 |
Hedge its Internal Fuel Usage and Other Related Activities Call Options and Swap Contracts Bought |  |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |  |
Derivative activity volume | 5.1 | 4.0 |

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