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Concentrations of Credit Risk - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023	Sep. 30, 2023
Concentration Risk [Line Items]
Restricted cash	$ 2,984,000		$ 2,984,000		$ 3,132,000
Outstanding letters of credit to be collateralized by amounts on deposit	3,000,000		3,000,000
Allowance for doubtful accounts	$ 0		$ 0		$ 0
Sales Revenue, Net [Member] \| American Airlines Inc. [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	0.00%	40.00%	0.00%	43.00%
Sales Revenue, Net [Member] \| United [Member] \| Customer Concentration Risk [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	98.00%	51.00%	97.00%	53.00%