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Summary of Significant Accounting Policies - Additional Information (Detail)
 3 Months Ended 12 Months Ended
Sep. 30, 2022
USD ($)
Sep. 30, 2022
USD ($)
Segment
Sep. 30, 2021
USD ($)
Sep. 30, 2020
USD ($)
Summary Of Significant Accounting Policies [Line Items]        
Number of operating segments | Segment   1    
Number of reportable segments | Segment   1    
Outstanding letters of credit to be collateralized by amounts on deposit, classified as restricted cash $ 3,300,000 $ 3,300,000 $ 3,400,000  
Allowance for obsolete expendable parts and supplies   634,000 380,000  
Asset impairment   171,824,000    
Lease revenue   $ 158,400,000 $ 170,200,000 $ 208,900,000
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]   Contract revenue Contract revenue Contract revenue
Current and non-current deferred credit balances 3,900,000 $ 3,900,000 $ 4,800,000  
Recognized deferred credits within contract revenue   900,000 2,400,000 $ 3,700,000
Contract assets balances 0 0 0  
Contract cost amortization   0 2,000,000.0 1,900,000
Amortization of heavy maintenance and major overhaul costs charged to depreciation and amortization expense   1,900,000 400,000 0
Deferred heavy maintenance balance, net of accumulated amortization 9,700,000 9,700,000 3,500,000  
Engine overhaul expense   23,600,000 31,400,000 40,500,000
Engine overhaul pass-through expense   21,700,000 16,800,000 7,000,000.0
Airframe check expense   22,100,000 51,100,000 23,500,000
Airframe check pass-through expense   3,200,000 20,500,000 7,200,000
Impairment loss   200,000 0 0
CRJ-900 Aircraft [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Impairment loss   15,200,000    
Customer Relationships [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Impairment loss on intangible assets   1,900,000 0 0
Customer Relationships [Member] | CRJ-900 Aircraft [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Impairment loss on intangible assets $ 1,900,000   0 0
Property and Equipment [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Asset impairment   109,700,000    
Other Long-lived Assets [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Asset impairment     0  
ROU Assets [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Asset impairment       $ 0
Aircraft [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Allowance for obsolete expendable parts and supplies   $ 3,800,000 $ 3,200,000  
Percentage leased   11.00%    
Aircraft and Rotable Spare Parts [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Property and equipment, salvage value, percentage 20.00% 20.00%    
Letter of Credit [Member]        
Summary Of Significant Accounting Policies [Line Items]        
Letter of credit facility, amount   $ 6,000,000.0