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Subsequent Events - Additional Information (Detail) $ in Millions |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended |
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Jul. 24, 2025 USD ($) ENGINE | Apr. 04, 2025 | Apr. 03, 2025 USD ($) ENGINE AIRFRAMES AIRCRAFT | Mar. 18, 2025 | Dec. 31, 2024 USD ($) AIRCRAFT | Dec. 24, 2024 USD ($) AIRFRAMES | Dec. 23, 2024 USD ($) | Oct. 01, 2024 USD ($) AIRCRAFT AIRFRAMES | Dec. 31, 2015 USD ($) | Jun. 30, 2025 USD ($) | Jun. 30, 2025 AIRCRAFT | Sep. 30, 2024 USD ($) ENGINE | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($) | Dec. 30, 2024 USD ($)
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of engines to be sold | ENGINE |  |  |  |  |  |  |  |  |  |  |  | 55 |  |  |
Impairment loss |  |  |  |  |  |  |  |  |  | $ 0.1 |  | $ 73.7 | $ 50.6 | $ 62.1 |
E-175 Aircraft [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft sold | AIRCRAFT |  |  |  |  |  |  |  |  |  |  | 18 |  |  |  |
Remaining balance |  |  |  |  |  |  |  |  | $ 73.4 |  |  |  |  |  |
CRJ-700 Aircraft [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft sold | AIRCRAFT |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
UST Loan [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum collateral coverage ratio |  |  |  | 0.91 |  |  | 0.99 |  |  |  |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of increase in CPA block hour rates |  | 3.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Number of engines to be sold | ENGINE |  |  | 23 |  |  |  |  |  |  |  |  |  |  |  |
Remaining balance |  |  |  |  |  |  |  | $ 73.4 |  |  |  |  |  |  |
Proceeds from Sale of Property, Plant, and Equipment | $ 4.6 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | United Capacity Purchase Agreement [Member] | United Airlines Inc [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock issued equivalent percentage of issued and outstanding capital stock |  | 6.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | Engines Held For Sale [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impairment Loss Held For Sale |  |  | $ 14.7 |  |  |  |  | $ 25.4 |  |  |  |  |  |  |
Subsequent Event [Member] | United Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loan balance forgiven |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4.5
Subsequent Event [Member] | E-175 Aircraft [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft sold | AIRCRAFT |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Subsequent Event [Member] | E-175 Aircraft [Member] | Aircraft Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected gross proceeds from sale of asset |  |  |  |  | $ 227.7 |  |  |  |  |  |  |  |  |  |
Expected proceeds from sale of asset |  |  |  |  | $ 84.7 |  |  |  |  |  |  |  |  |  |
Number of aircraft classified as assets held for sale | AIRCRAFT |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Number of aircraft sold | AIRCRAFT |  |  |  |  | 18 |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | E-175 Aircraft [Member] | United Aircraft Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected gross proceeds from sale of asset |  |  |  |  |  |  |  | $ 84.7 |  |  |  | $ 227.7 |  |  |
Expected proceeds from sale of asset |  |  | $ 16.3 |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft classified as assets held for sale | AIRCRAFT |  |  |  |  | 18 |  |  | 18 |  |  |  |  |  |  |
Gross proceeds from sale of asset |  |  |  |  |  |  |  | $ 120.6 |  |  |  |  |  |  |
Number of aircraft sold | AIRCRAFT |  |  | 23 |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | C R J 900 Airframes [Member] | Aircraft Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft sold | AIRFRAMES |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |
Subsequent Event [Member] | C R J 900 Airframes [Member] | Airframe Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft classified as assets held for sale | AIRFRAMES |  |  |  |  |  | 29 |  |  |  |  |  |  |  |  |
Gross proceeds from sale of asset |  |  | $ 9.1 |  |  |  | $ 19.0 |  |  |  |  |  |  |  |
Number of aircraft sold | AIRFRAMES |  |  | 14 |  |  | 15 |  |  |  |  |  |  |  |  |
Impairment loss |  |  |  |  |  | $ 6.7 |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | CRJ-700 Aircraft [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from sale of asset |  |  |  |  |  |  |  | $ 11.0 |  |  |  |  |  |  |
Net proceeds from sale of asset |  |  |  |  |  |  |  | $ 6.8 |  |  |  |  |  |  |
Subsequent Event [Member] | CF34-8C Engines [Member] | Airframe Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of aircraft sold | AIRFRAMES |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Subsequent Event [Member] | UST Loan [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum collateral coverage ratio |  |  |  |  |  |  | 1.55 |  |  |  |  |  |  |  |
Number of engine sold | ENGINE | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Member] | UST Loan [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum collateral coverage ratio |  |  |  | 0.91 |  |  | 0.99 |  |  |  |  |  |  |  |
Subsequent Event [Member] | UST Loan [Member] | Aircraft Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from sale of asset |  |  |  |  |  |  |  | $ 22.4 |  |  |  |  |  |  |
Repayments of debt |  |  |  |  |  |  |  | $ 21.0 |  |  |  |  |  |  |
Subsequent Event [Member] | UST Loan [Member] | C R J 900 Airframes [Member] | Airframe Purchase Agreement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from sale of asset |  |  | $ 28.1 |  |  |  |  |  |  |  |  |  |  |  |

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