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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions	3 Months Ended
	Dec. 31, 2024 USD ($) gal	Dec. 31, 2023 gal	Sep. 30, 2024 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedging positions or payable amounts secured under credit facility \| $	$ 9,900,000		$ 14,200,000
Prepaid expense and other current assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregated cash posted as collateral in normal course of business \| $	4,000,000
Interest rate swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value \| $	$ 77,100,000		52,000,000.0
Percentage of market risk exposure of long term debt	38.00%
Fair Value \| $	$ 300,000		$ (300,000)
Call Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	5.9	8.8
Call Option \| Synthetic calls
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	52.2	61.4
Put Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	8.4	6.6
Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	17.2	14.2
Swap Contracts Bought \| Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	1.1	0.2
Future Contracts \| Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	18.5	20.7
Hedge its Internal Fuel Usage and Other Related Activities Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	5.9	5.3