Balance Sheet Information - Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Expendable parts and supplies, net:
Expendable parts and supplies	$ 31,437	$ 29,297
Less: obsolescence and other	(5,096)	(4,830)
Expendable parts and supplies, net	26,341	24,467
Prepaid expenses and other current assets:
Prepaid aviation insurance	2,355	2,171
Lease incentives	1,875	1,445
Other	3,004	3,269
Prepaid expenses and other current assets	7,234	6,885
Property and equipment, net:
Property and equipment-gross	1,544,157	1,621,437
Less: accumulated depreciation	(471,331)	(469,546)
Property and equipment-net	1,072,826	1,151,891
Other assets:
Investments in equity securities	16,586	25,149
Lease incentives	13,085	10,957
Other	15	15
Other assets	29,686	36,121
Other accrued expenses:
Accrued property taxes	4,751	8,783
Accrued interest	4,485	2,565
Accrued vacation	5,109	5,936
Other	17,977	16,373
Other accrued expenses	32,322	33,657
Other noncurrent liabilities:
Warrant liabilities	25,225	21,964
Lease incentive obligations	6,492	6,358
Other	5,254	6,269
Other noncurrent liabilities	36,971	34,591
Aircraft and Other Flight Equipment [Member]
Property and equipment, net:
Property and equipment-gross	1,533,992	1,611,544
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	5,399	4,934
Leasehold Improvements [Member]
Property and equipment, net:
Property and equipment-gross	2,776	2,776
Vehicles [Member]
Property and equipment, net:
Property and equipment-gross	993	1,184
Building [Member]
Property and equipment, net:
Property and equipment-gross	699	699
Furniture and Fixtures [Member]
Property and equipment, net:
Property and equipment-gross	$ 298	$ 300