Derivatives and Hedging-Disclosures and Fair Value Measurements - Additional Information (Detail) gal in Millions	3 Months Ended
	Dec. 31, 2021 USD ($) gal	Dec. 31, 2020 gal	Sep. 30, 2021 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedging positions or payable amounts secured under credit facility | $	$ 0		$ 0
Prepaid expense and other current assets
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Aggregated cash posted as collateral in normal course of business | $	6,100,000
Interest rate swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional Value | $	$ 57,800,000		59,000,000.0
Percentage of market risk exposure of long term debt	56.00%
Fair Value | $	$ (900,000)		$ (1,600,000)
Call Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	34.6	8.5
Call Option | Synthetic calls
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	52.6	86.5
Put Option
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	4.5	5.1
Swap Contracts Bought
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	14.8	11.2
Swap Contracts Bought | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume		0.6
Future Contracts | Long
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	1.1	3.8
Future Contracts | Short
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative activity volume	26.7	29.1
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	5.0	5.1