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Summary of Significant Accounting Policies - Additional Information (Detail) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Mar. 31, 2022 USD ($) | Mar. 31, 2021 USD ($) | Mar. 31, 2022 USD ($) Air-craft | Mar. 31, 2021 USD ($) | Sep. 30, 2021 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Deferred revenue | $ 0.8 |  | $ 5.0 |  |
Lease incentive assets | 14.7 |  | 14.7 |  |
Lease incentive obligations | 11.5 |  | 11.5 |  |
Amounts deferred for supplemental rent payments | 1.9 |  | 1.9 |  |
Current and non-current deferred credit contract liability balances | 4.4 |  | 4.4 |  | $ 4.8
Recognized deferred credits within contract revenue | 0.2 | $ 1.1 | 0.4 | $ 1.9 |
Amortization of heavy maintenance and major overhaul costs charged to depreciation and amortization expense | 0.4 | 0.0 | 0.6 | 0.0 |
Deferred heavy maintenance balance, net of accumulated amortization | 5.3 |  | 5.3 |  | $ 3.5
Engine overhaul expense | 4.8 | 6.9 | 10.1 | 21.3 |
Engine overhaul pass-through expense | 4.6 | 2.2 | 8.4 | 11.8 |
Airframe check expense | 4.7 | 14.1 | 13.8 | 24.2 |
Airframe check pass-through expense | 0.5 | 5.6 | $ 0.5 | 12.7 |
Aircraft [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Percentage leased |  |  | 11.00% |  |
GoJet Agreements [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Lease revenue recognized | $ 6.8 |  | $ 13.3 |  |
CRJ 700 [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Number of aircraft to be leased | Air-craft |  |  | 18 |  |
Operating lease, term of contract | 9 years |  | 9 years |  |
Contract Revenue [Member] |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |
Lease revenue | $ 39.5 | $ 41.0 | $ 79.8 | $ 90.5 |

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