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Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions | 12 Months Ended
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Sep. 30, 2024 USD ($) gal | Sep. 30, 2023 USD ($) gal
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Hedging positions and payable amounts secured under credit facility | $ 14,200,000 | $ 100,000
Prepaid expense and other current assets |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Aggregated cash posted as collateral in normal course of business | 300,000 |
Interest rate swap |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Notional Value | 52,000,000 | 55,500,000
Fair Value | $ (300,000) | $ 1,600,000
Percentage of market risk exposure of long term debt | 25.00% |
Call Option |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 6.0 | 8.1
Notional Value | $ 18,200,000 | $ 25,600,000
Fair Value |  | $ 1,700,000
Call Option | Minimum |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Fair Value | $ 100,000 |
Call Option | Synthetic calls |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 52.1 | 57.3
Notional Value | $ 133,900,000 | $ 164,200,000
Fair Value | $ (9,200,000) | $ 4,000,000
Put Option |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 7.1 | 4.2
Notional Value | $ 12,700,000 | $ 9,300,000
Fair Value | $ 300,000 | $ 100,000
Swap Contracts Bought |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 12.2 | 9.3
Notional Value | $ 29,400,000 | $ 26,100,000
Fair Value | $ (2,800,000) | $ 1,900,000
Future Contracts | Short |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 6.2 | 10.0
Notional Value | $ 14,000,000 | $ 28,200,000
Fair Value | $ 600,000 | $ (3,800,000)
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 | gal | 8.4 | 7.7
Notional Value | $ 20,300,000 | $ 19,100,000
Fair Value | $ (2,300,000) | $ 2,900,000
Swap Contracts |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Derivative activity volume | gal | 0.7 |
Notional Value | $ 1,400,000 |
Swap Contracts | Minimum |  |
Derivative Instruments and Hedging Activities Disclosures [Line Items] |  |
Fair Value | $ 100,000 |

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