Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions	6 Months Ended
	Mar. 31, 2025 USD ($) gal	Mar. 31, 2024 gal	Sep. 30, 2024 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedging positions or payable amounts secured under credit facility | $	$ 3,700,000		$ 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 | $	2,800,000
Interest rate swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | $	$ 76,300,000		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	2.6	3.5
Call Option | Synthetic calls
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	30.9	35.1
Put Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	4.0	3.5
Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	9.0	7.5
Swap Contracts Bought | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	1.2	0.2
Future Contracts | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	15.5	13.9
Hedge its Internal Fuel Usage and Other Related Activities Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	4.2	3.8