Concentrations of Credit Risk - Additional Information (Detail) - USD ($)	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Concentration Risk [Line Items]
Restricted cash	$ 3,132,000	$ 3,342,000
Outstanding letters of credit to be collateralized by amounts on deposit	3,100,000	3,300,000
Allowance for doubtful accounts	$ 0	$ 0
Sales Revenue, Net [Member] \| American Airlines Inc. [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%	45.00%	45.00%
Sales Revenue, Net [Member] \| United [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	73.00%	48.00%	52.00%

Amount of allowance for credit loss on accounts receivable.

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