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Leases - Additional Information Related to Leases (Details) - aircraft | Jun. 30, 2019 | Sep. 30, 2018 | Jun. 30, 2018
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Lessee, Lease, Description [Line Items] |  |  |
Weighted-average remaining lease term - operating leases | 10 years |  | 10 years
Weighted-average remaining lease term - finance leases | 5 years |  | 5 years
Weighted-average discount rate - operating leases | 5.30% |  | 5.10%
Weighted-average discount rate - finance leases | 53.20% |  | 6.70%
Embraer ERJ 145 |  |  |
Lessee, Lease, Description [Line Items] |  |  |
Number of leased aircraft |  | 54 |

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