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Leases - Additional Information (Detail)
 12 Months Ended
Sep. 30, 2024
USD ($)
AirCraft
Sep. 30, 2023
USD ($)
Sep. 30, 2022
USD ($)
Sep. 30, 2021
USD ($)
Lessee, Lease, Description [Line Items]        
Number of leased aircraft under finance lease | AirCraft 2      
Finance lease obligations $ 4,700,000      
Operating lease, right-of-use assets 7,231,000 $ 9,709,000    
Operating lease current liabilities 1,681,000 3,510,000    
Operating lease noncurrent liabilities 6,863,000 8,077,000    
Financing lease current $ 1,800,000      
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Current portion of long-term debt and finance leases ($6,604 and $20,500 from related party)      
Number of leased aircraft | AirCraft 32      
Financing lease noncurrent liabilities $ 2,900,000      
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Long-term debt and finance leases, excluding current portion ($30,914 and $30,630 from related party)      
Operating lease payments in operating cash flows $ 4,585,000 9,476,000 $ 36,262,000  
Aggregate rental expense under all operating aircraft, equipment and facility lease 13,900,000 12,200,000 43,400,000  
Financing lease payments in operating cash flows 2,000,000 1,200,000    
Financing lease payments in financing cash flows 65,300,000 15,100,000    
Impairment loss 0 0 10,500,000  
Deferred income taxes 8,173,000 8,414,000    
Cash, cash equivalents and availability under lines of credit $ 18,630,000 $ 36,072,000 $ 61,025,000 $ 123,867,000