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Long-Term Debt and Other Borrowings - Additional Information (Detail) $ in Thousands |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jun. 28, 2018 USD ($) Aircraft | Jun. 27, 2018 USD ($) Aircraft | Jun. 30, 2018 USD ($) Aircraft | Jun. 30, 2018 USD ($) Aircraft | Jun. 30, 2018 USD ($) Aircraft | Dec. 31, 2017 USD ($) | Sep. 30, 2017 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |
Property and equipment, net |  |  | $ 1,239,548 | $ 1,239,548 | $ 1,239,548 |  | $ 1,192,448
Long-Term Debt |  |  | $ 994,102 | 994,102 | 994,102 |  | $ 956,918
Non-cash lease termination expense |  |  |  | $ 15,109 | $ 15,109 |  |
CRJ-900 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Refinanced debt |  | $ 16,000 |  |  |  |  |
Number of aircraft under refinanced debt | Aircraft |  | 6 | 9 | 9 | 9 |  |
Refinanced debt due period |  | 2019 |  |  |  |  |
Debt instrument, face amount | $ 69,600 | $ 27,500 | $ 27,500 | $ 27,500 | $ 27,500 | $ 74,900 |
Net cash proceeds after transaction related fees |  | $ 10,400 |  |  |  |  |
Long term debt interest rate description | LIBOR plus a spread ranging from 3.50% for the senior promissory notes to 7.50% for the subordinated promissory notes |  |  |  | LIBOR plus 3.50%. |  |
Long term debt, basis spread on variable rate |  | 3.50% |  |  |  |  |
Number of aircraft purchased | Aircraft | 9 |  |  |  |  |  |
Payment for aircraft purchased | $ 76,500 |  |  |  |  |  |
Non-cash lease termination expense | 15,100 |  |  |  |  |  |
Future goods and services credits | 4,500 |  |  |  |  |  |
Loan forgiveness for loans | $ 5,600 |  |  |  |  |  |
Equipment Notes [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-Term Debt |  |  | 217,900 | 217,900 | $ 217,900 |  |
Senior Notes Due 2020 [Member] | CRJ-900 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Debt instrument, face amount |  |  | $ 67,300 | 67,300 | 67,300 |  |
Long term debt, basis spread on variable rate | 3.50% |  | 3.50% |  |  |  |
Subordinated Notes Due 2020 [Member] | CRJ-900 [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long term debt, basis spread on variable rate | 7.50% |  | 7.50% |  |  |  |
Aircraft and Equipment [Member] | Pledged as Collateral [Member] |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Property and equipment, net |  |  | $ 1,170,400 | $ 1,170,400 | $ 1,170,400 |  |

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