Balance Sheet Information - Summary of Certain Significant Amounts Included in Condensed Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Sep. 30, 2023
Expendable parts and supplies, net:
Expendable parts and supplies	$ 40,968	$ 39,630
Less: expendable parts warranty	(7,091)	(6,295)
Less: obsolescence	(4,403)	(4,090)
Expendable parts and supplies, net	29,474	29,245
Prepaid expenses and other current assets:
Prepaid aviation insurance	2,290	3,176
Prepaid vendors	733	143
Prepaid other insurance	520	1,205
Lease incentives	143	1,125
Prepaid fuel and other	864	1,645
Prepaid expenses and other current assets	4,550	7,294
Property and equipment, net:
Property and equipment-gross	792,193	1,049,203
Less: accumulated depreciation	(262,714)	(351,181)
Property and equipment-net	529,479	698,022
Other assets:
Investments in equity securities	11,397	20,320
Lease incentives	883	954
Contract asset	7,763	8,756
Other	515	516
Other assets	20,558	30,546
Other accrued expenses:
Accrued property taxes	3,406	5,281
Accrued interest	3,174	3,447
Accrued vacation	7,251	6,763
Accrued lodging	3,920	3,984
Accrued maintenance	1,280	2,117
Accrued simulator costs		1,006
Accrued employee benefits	1,086	1,450
Accrued fleet operating expense	1,808	650
Other	4,600	2,303
Other accrued expenses	26,525	27,001
Other noncurrent liabilities:
Warrant liabilities	25,225	25,225
Lease incentive obligations	1,050	1,050
Long-term employee benefits	380	429
Other	1,820	1,818
Other noncurrent liabilities	28,475	28,522
Aircraft and Other Flight Equipment [Member]
Property and equipment, net:
Property and equipment-gross	782,725	1,039,782
Other Machinery and Equipment [Member]
Property and equipment, net:
Property and equipment-gross	$ 9,468	$ 9,421