Leases - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Dec. 31, 2022 USD ($) AirCraft	Sep. 30, 2023 USD ($) AirCraft	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Sep. 23, 2005 USD ($) AirCraft
Lessee, Lease, Description [Line Items]
Number of leased aircraft under finance lease | AirCraft		15
Number of spare engines leased under finance lease | AirCraft		3
Finance lease obligations		$ 67,600,000
Operating lease, right-of-use assets		9,709,000	$ 43,090,000
Operating lease current liabilities		3,510,000	17,233,000
Operating lease noncurrent liabilities		8,077,000	16,732,000
Financing lease current		$ 57,700,000
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]		Current portion of long-term debt and finance leases ($20,500 and $0 from related party)
Number of leased aircraft | AirCraft		18
Financing lease noncurrent liabilities		$ 9,900,000
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]		Long-term debt and finance leases, excluding current portion ($30,630 and $0 from related party)
Operating lease payments in operating cash flows		$ 9,476,000	36,262,000	$ 47,612,000
Aggregate rental expense under all operating aircraft, equipment and facility lease		12,200,000	43,400,000	44,600,000
Financing lease payments in operating cash flows		1,200,000	300,000
Financing lease payments in financing cash flows		15,100,000	2,500,000
Impairment loss		0	10,500,000	0
Deferred income taxes		8,414,000	17,719,000
Cash, cash equivalents and availability under lines of credit		$ 36,072,000	$ 61,025,000	$ 123,867,000	$ 102,841,000
RASPRO Aircraft Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Deferred income taxes						$ 4,000,000
Number of aircraft lease terminated | AirCraft	15
Buyout pricing	$ 25,000,000
CRJ-900 Aircraft [Member] | RASPRO Aircraft Lease Agreement [Member]
Lessee, Lease, Description [Line Items]
Number of leased aircraft | AirCraft							15
Cash, cash equivalents and availability under lines of credit							$ 35,000,000