Leases - Additional Information Related to Leases (Details) - aircraft	Sep. 30, 2019	Sep. 30, 2018
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term - operating leases	11 years	11 years
Weighted-average remaining lease term - finance leases	5 years	5 years
Weighted-average discount rate - operating leases	5.30%	5.20%
Weighted-average discount rate - finance leases	44.80%	39.50%
Embraer ERJ 145
Lessee, Lease, Description [Line Items]
Number of leased aircraft		54