Balance Sheet Information - Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Expendable parts and supplies, net:
Expendable parts and supplies	$ 32,013	$ 31,913
Less: obsolescence and other	(6,504)	(5,198)
Expendable parts and supplies, net	25,509	26,715
Prepaid expenses and other current assets:
Prepaid aviation insurance	1,026	2,618
Prepaid vendors	906	1,310
Prepaid other insurance	798	1,268
Lease incentives	143	352
Prepaid fuel and other	1,080	1,068
Prepaid expenses and other current assets	3,953	6,616
Property and equipment, net:
Property and equipment-gross	1,364,700	1,270,563
Less: accumulated depreciation	(419,155)	(405,309)
Property and equipment-net	945,545	865,254
Other assets:
Investments in equity securities	13,408	15,178
Lease incentives	1,061	1,097
Other	515	15
Other assets	14,984	16,290
Other accrued expenses:
Accrued property taxes	6,066	5,866
Accrued interest	5,016	2,882
Accrued vacation	7,768	4,746
Accrued lodging	3,529	3,795
Accrued maintenance	2,154	1,453
Accrued liability on government payroll program		2,967
Accrued simulator costs	149	1,045
Accrued employee benefits	1,097	1,679
Accrued fleet operating expense	1,232	1,606
Other	3,550	2,961
Other accrued expenses	30,561	29,000
Other noncurrent liabilities:
Warrant liabilities	25,225	25,225
Lease incentive obligations	1,050	1,050
Long-term employee benefits	843	1,123
Other	1,820	1,821
Other noncurrent liabilities	28,938	29,219
Aircraft and Other Flight Equipment [Member]
Property and equipment, net:
Property and equipment-gross	1,354,137	1,260,143
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	5,709	5,577
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	1,003	992
Building [Member]
Property and equipment, net:
Property and equipment-gross	777	777
Furniture and Fixtures [Member]
Property and equipment, net:
Property and equipment-gross	$ 298	$ 298