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Summary of Significant Accounting Policies - Additional Information (Detail) | 12 Months Ended
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Sep. 30, 2023 USD ($) Segment AirCraft | Sep. 30, 2022 USD ($) | Sep. 30, 2021 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |
Number of operating segments | Segment | 1 |  |
Number of reportable segments | Segment | 1 |  |
Outstanding letters of credit to be collateralized by amounts on deposit, classified as restricted cash | $ 3,100,000 | $ 3,300,000 |
Asset impairment | 54,343,000 | 171,824,000 |
Impairment loss held for sale | 50,600,000 | 62,100,000 | $ 0
Impairment loss on intangible assets | 54,343,000 | 171,824,000 |
Lease revenue | $ 144,700,000 | $ 158,400,000 | $ 170,200,000
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration] | Contract revenue | Contract revenue | Contract revenue
Current and non-current deferred credit balances | $ 5,100,000 | $ 3,900,000 |
Recognized deferred credits within contract revenue | 1,700,000 | 900,000 | $ 2,400,000
Contract assets balances | 8,800,000 | 0 |
Contract cost amortization | 1,000,000 | 0 | 2,000,000
Amortization of heavy maintenance and major overhaul costs charged to depreciation and amortization expense | 3,100,000 | 1,900,000 | 400,000
Deferred heavy maintenance balance, net of accumulated amortization | 8,000,000 | 9,700,000 |
Engine overhaul expense | 32,400,000 | 23,600,000 | 31,400,000
Engine overhaul pass-through expense | 31,900,000 | 21,700,000 | 16,800,000
Airframe check expense | 23,400,000 | 22,100,000 | 51,100,000
Airframe check pass-through expense | 16,900,000 | 3,200,000 | 20,500,000
Impairment loss | 0 | 10,500,000 | 0
Net (loss) income | (120,116,000) | (182,678,000) | 16,588,000
Net cash (used in) provided by operating activities | (24,091,000) | 13,362,000 | 132,871,000
Working capital deficit | 129,300,000 |  |
Accumulated deficit | (71,119,000) | 48,997,000 |
Cash and cash equivalents | $ 32,940,000 | 57,683,000 |
CRJ-900 Aircraft [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Number of aircraft classified as assets held for sale | AirCraft | 14 |  |
Customer Relationships [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Impairment loss on intangible assets | $ 3,700,000 | 1,900,000 | 0
Customer Relationships [Member] | CRJ-900 Aircraft [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Impairment loss on intangible assets | 3,700,000 | 1,900,000 | 0
Property and Equipment [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Asset impairment | 0 | 109,700,000 | 0
Other Long-lived Assets [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Asset impairment | 0 | 109,700,000 | $ 0
Long Lived Assets [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Asset impairment | 0 |  |
Aircraft [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Allowance for obsolete expendable parts and supplies | $ 4,100,000 | $ 3,800,000 |
Percentage leased | 1.00% |  |
Aircraft and Rotable Spare Parts [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Property and equipment, salvage value, percentage | 20.00% |  |
Letter of Credit [Member] |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |
Letter of credit facility, amount | $ 6,000,000 |  |

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