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Concentrations of Credit Risk - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2023 | Mar. 31, 2022 | Sep. 30, 2022
Concentration Risk [Line Items] |  |  |  |  |
Restricted cash | $ 3,144,000 |  | $ 3,144,000 |  | $ 3,342,000
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 | 40.00% | 46.00% | 43.00% | 47.00% |
Sales Revenue, Net [Member] | United [Member] | Customer Concentration Risk [Member] |  |  |  |  |
Concentration Risk [Line Items] |  |  |  |  |
Concentration risk, percentage | 55.00% | 47.00% | 53.00% | 47.00% |

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