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Summary of Significant Accounting Policies - Additional Information (Detail) |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Apr. 23, 2021 USD ($) | Apr. 15, 2021 USD ($) | Apr. 30, 2021 USD ($) | Mar. 31, 2021 USD ($) Air-craft | Feb. 28, 2021 USD ($) | Mar. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Mar. 31, 2020 USD ($) | Mar. 31, 2021 USD ($) Air-craft | Mar. 31, 2020 USD ($) | Sep. 30, 2020 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of aircrafts operated | Air-craft |  |  |  |  |  |  |  |  | 163 |  |
Lease incentive assets |  |  |  | $ 4,800,000 |  | $ 4,800,000 |  |  | $ 4,800,000 |  |
Lease incentive obligations |  |  |  | 4,200,000 |  | 4,200,000 |  |  | 4,200,000 |  |
Deferred revenue |  |  |  |  |  | 4,900,000 |  |  |  |  |
Lease termination expense |  |  |  | 4,500,000 |  |  |  |  |  |  |
Current and non-current deferred credit balances |  |  |  | 5,200,000 |  | 5,200,000 |  |  | 5,200,000 |  | $ 8,500,000
Recognized deferred credits within contract revenue |  |  |  |  |  | 1,100,000 |  | $ 1,900,000 | 900,000 | $ 2,000,000.0 |
Deferred heavy maintenance balance, net of accumulated amortization |  |  |  | $ 1,200,000 |  | 1,200,000 |  |  | 1,200,000 |  | $ 0
Engine overhaul expense |  |  |  |  |  | 6,900,000 |  | 14,500,000 | 21,300,000 | 25,100,000 |
Engine overhaul pass-through expense |  |  |  |  |  | 2,200,000 |  | 700,000 | 11,800,000 | 2,600,000 |
Airframe check expense |  |  |  |  |  | 14,100,000 |  | 10,500,000 | 24,200,000 | 17,800,000 |
Airframe check pass-through expense |  |  |  |  |  | 5,600,000 |  | 3,900,000 | 12,700,000 | 5,100,000 |
Payroll Support Program Extension, amount granted |  |  |  |  | $ 48,700,000 |  |  |  |  |  |
Payroll Support Program Extension, additional amount granted |  |  |  |  | 7,300,000 |  |  |  |  |  |
Payroll Support Program Extension, total amount granted |  |  |  |  | $ 56,000,000.0 |  |  |  |  |  |
Payroll support government funds |  |  |  |  |  | $ 56,000,000.0 |  |  | 67,300,000 |  |
deferred payments |  |  |  |  |  |  | $ 11,300,000 |  | $ 0 |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Payroll Support Program Extension, additional amount granted |  |  | $ 7,300,000 |  |  |  |  |  |  |  |
Third Payroll Support Program, eligible and estimated amount |  | $ 52,200,000 |  |  |  |  |  |  |  |  |
Third Payroll Support Program, amount received | $ 26,100,000 |  |  |  |  |  |  |  |  |  |
Aircraft [Member] |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Percentage leased |  |  |  |  |  |  |  |  | 10.00% |  |
CRJ 700 [Member] |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of aircraft to be leased | Air-craft |  |  |  | 6 |  |  |  |  |  |  |
Number of aircrafts operated | Air-craft |  |  |  | 20 |  |  |  |  |  |  |
Operating lease, term of contract |  |  |  | 9 years |  | 9 years |  |  | 9 years |  |
Contract Revenue [Member] |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Lease revenue |  |  |  |  |  | $ 18,100,000 |  | $ 52,400,000 | $ 67,600,000 | $ 105,700,000 |

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