Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions	6 Months Ended
	Mar. 31, 2024 USD ($) gal	Mar. 31, 2023 gal	Sep. 30, 2023 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedging positions or payable amounts secured under credit facility | $	$ 2,200,000		$ 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 | $	2,100,000
Interest rate swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | $	$ 53,800,000		55,500,000
Percentage of market risk exposure of long term debt	39.00%
Fair Value | $	$ 800,000		$ 1,600,000
Call Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	3.5	6.5
Call Option | Synthetic calls
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	35.1	36.7
Put Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	3.5	2.4
Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	7.5	5.4
Swap Contracts Bought | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	0.2	13.5
Future Contracts | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	13.9	1.8
Hedge its Internal Fuel Usage and Other Related Activities Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	3.8	3.7