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Assets Held for Sale - Additional Information (Detail) $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2025 USD ($) ENGINE AIRFRAMES | Mar. 31, 2025 ENGINE AIRFRAMES | Sep. 30, 2024 USD ($) ENGINE AIRFRAMES AIRCRAFT | Sep. 30, 2023 USD ($) AIRCRAFT | Sep. 30, 2022 USD ($)
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Impairment loss held for sale | $ 100 |  | $ 73,700 | $ 50,600 | $ 62,100
Aircraft held for sale current | 60,311 |  | $ 5,741 | 57,722 |
Number of aircraft split up to airframes | AIRFRAMES |  |  | 7 |  |
Number of aircraft split up to engines | ENGINE |  |  | 14 |  |
Aircraft held for sale | 0 |  | $ 86,605 | $ 12,000 |
Number of engines held to sale | ENGINE |  |  | 55 |  |
Number of airframes to be sold | AIRFRAMES |  |  | 26 |  |
Current Assets [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Aircraft held for sale current | $ 60,300 |  | $ 5,700 |  |
Noncurrent Assets [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Aircraft held for sale |  |  | $ 86,600 |  |
Without Active Purchase Agreement [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of engines held to sale | ENGINE |  |  | 19 |  |
Number of airframes to be sold | AIRFRAMES |  |  | 26 |  |
CRJ-900 [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft held for sale | AIRCRAFT |  |  | 8 | 15 |
Number of airframes without engines | AIRCRAFT |  |  | 26 |  |
Number of aircraft sold | AIRCRAFT |  |  | 15 |  |
Gross proceeds from sale of asset |  |  | $ 71,500 |  |
Number of aircraft split up | AIRCRAFT |  |  | 7 |  |
Aircraft held for sale |  |  | $ 92,300 |  |
GE Model [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft held for sale | AIRCRAFT |  |  | 77 |  |
Airframes [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft held for sale | AIRFRAMES | 21 | 27 | 26 |  |
Airframes [Member] | RASPRO Aircraft Lease Agreement [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | AIRFRAMES |  |  | 15 |  |
Gross proceeds from sale of asset |  |  | $ 18,800 |  |
Engines [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft held for sale | ENGINE | 34 | 46 | 55 |  |
Number of aircraft sold | ENGINE |  |  | 30 |  |
Gross proceeds from sale of asset |  |  | $ 19,500 |  |
29 Enginers [Member] | RASPRO Aircraft Lease Agreement [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 29 |  |
Gross proceeds from sale of asset |  |  | $ 18,900 |  |
Remaining Engine [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Gross proceeds from sale of asset |  |  | $ 700 |  |
23 Engines [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 23 |  |
Gross proceeds from sale of asset |  |  | $ 11,500 |  |
3 Engines [Member] | UST Loan [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 3 |  |
Gross proceeds from sale of asset |  |  | $ 1,500 |  |
12 Engines [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 12 |  |
Gross proceeds from sale of asset |  |  | $ 54,200 |  |
14 Enginers [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 14 |  |
Gross proceeds from sale of asset |  |  | $ 24,700 |  |
9 Enginers [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 9 |  |
Gross proceeds from sale of asset |  |  | $ 8,800 |  |
8 Enginers [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft sold | ENGINE |  |  | 8 |  |
Gross proceeds from sale of asset |  |  | $ 12,900 |  |
Proceeds from sale of asset |  |  | $ 4,400 |  |
CRJ-700 [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of aircraft held for sale | AIRCRAFT |  |  | 2 |  |
Gross proceeds from sale of asset |  |  | $ 11,000 |  |
CRJ-900 Airframes [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of airframes sold | AIRFRAMES | 6 |  |  |  |
GE Model CF34-8C [Member] |  |  |  |  |
Long Lived Assets Held For Sale [Line Items] |  |  |  |  |
Number of engine sold | ENGINE | 13 |  |  |  |

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