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Balance Sheet Information - Additional Information (Detail) - USD ($) | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2021 | Jul. 31, 2021 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Feb. 28, 2022 | Feb. 28, 2021
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Depreciation expense |  |  | $ 40,000,000 | $ 60,200,000 | $ 80,500,000 |  |
Estimated initial equity warrant asset value |  |  |  |  |  |  | $ 16,400,000
Investments in equity securities |  |  | 300,000 | 20,320,000 |  |  |
Total net unrealized (loss)/gain |  |  | (6,100,000) | 5,400,000 |  |  |
Estimated initial warrant asset value |  |  |  |  |  | $ 3,200,000 |
Total realized gain (loss) on equity securities |  |  | 8,000,000 | 0 |  |  |
Aggregate carrying amount of investments in equity securities |  |  | 300,000 | 20,300,000 |  |  |
Investments without readily determinable fair value |  |  | 300,000 | 8,800,000 |  |  |
United Capacity Purchase Agreement [Member] |  |  |  |  |  |  |
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Realized and unrealized gain (loss) on investment |  |  | 7,200,000 |  |  |  |
Debt reduction |  |  | 12,600,000 |  |  |  |
Archer Aviation, Inc. [Member] | Level 1 [Member] |  |  |  |  |  |  |
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Proceeds from sale |  |  | 9,600,000 |  |  |  |
Gain on sale |  |  | 800,000 |  |  |  |
Realized and unrealized gain (loss) on investment |  |  | (2,700,000) | $ 5,600,000 |  |  |
Heart Aerospace Incorporated [Member] | Forward Purchase Contract [Member] | Preferred Stock [Member] |  |  |  |  |  |  |
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Purchase of preferred stock |  | $ 5,000,000 |  |  |  |  |
Initial investment in preferred stock measured at cost |  | $ 5,000,000 |  |  |  |  |
VTOL Aircraft, XTI Aerospace, Inc [Member] | Level 1 [Member] |  |  |  |  |  |  |
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Realized and unrealized gain (loss) on investment |  |  | (3,500,000) |  |  |  |
Investments in equity securities |  |  | $ 100,000 |  |  |  |
Class A [Member] | Archer Aviation, Inc. [Member] |  |  |  |  |  |  |
Condensed Balance Sheet Statements Captions [Line Items] |  |  |  |  |  |  |
Number of shares sold | 500,000 |  |  |  |  |  |
Proceeds from sale | $ 5,000,000 |  |  |  |  |  |
Total grant date value, Additional warrant to purchase shares | $ 5,600,000 |  |  |  |  |  |

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