Balance Sheet Information - Summary of Certain Significant Amounts Included in Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Sep. 30, 2022
Expendable parts and supplies, net:
Expendable parts and supplies	$ 39,630	$ 31,913
Less: expendable parts warranty	(6,295)	(1,373)
Less: obsolescence	(4,090)	(3,825)
Expendable parts and supplies, net	29,245	26,715
Prepaid expenses and other current assets:
Prepaid aviation insurance	3,176	2,618
Prepaid vendors	143	1,310
Prepaid other insurance	1,205	1,268
Lease Incentives	1,125	352
Prepaid fuel and other	1,645	1,068
Prepaid expenses and other current assets	7,294	6,616
Property and equipment, net:
Property and equipment-gross	1,049,203	1,270,563
Less: accumulated depreciation	(351,181)	(405,309)
Property and equipment-net	698,022	865,254
Other assets:
Investments in equity securities	20,320	15,178
Lease incentives	954	1,097
Contract asset	8,756
Other	516	15
Other assets	30,546	16,290
Other accrued expenses:
Accrued property taxes	5,281	5,866
Accrued interest	3,447	2,882
Accrued vacation	6,763	4,746
Accrued lodging	3,984	3,795
Accrued maintenance	2,117	1,453
Accrued liability on government payroll program		2,967
Accrued simulator costs	1,006	1,045
Accrued employee benefits	1,450	1,679
Accrued fleet operating expense	650	1,606
Short term lease incentive liability	97	97
Other	2,206	2,864
Other accrued expenses	27,001	29,000
Other noncurrent liabilities:
Warrant liabilities	25,225	25,225
Lease incentive obligations	1,050	1,050
Long-term employee benefits	429	1,123
Other	1,818	1,821
Other noncurrent liabilities	28,522	29,219
Aircraft and Other Flight Equipment [Member]
Property and equipment, net:
Property and equipment-gross	1,039,782	1,260,143
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	$ 9,421	$ 10,420