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Concentrations of Credit Risk - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Jun. 30, 2022
Jun. 30, 2021
Jun. 30, 2022
Jun. 30, 2021
Sep. 30, 2021
Concentration Risk [Line Items]          
Restricted cash $ 3,348,000   $ 3,348,000   $ 3,350,000
Outstanding letters of credit to be collateralized by amounts on deposit 3,300,000   3,300,000    
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 46.00% 45.00% 46.00% 46.00%  
Sales Revenue, Net [Member] | United [Member] | Customer Concentration Risk [Member]          
Concentration Risk [Line Items]          
Concentration risk, percentage 47.00% 51.00% 48.00% 52.00%