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Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Jun. 30, 2023
USD ($)
AirCraft
Jun. 30, 2023
USD ($)
Jun. 30, 2022
USD ($)
Jun. 30, 2023
USD ($)
AirCraft
Jun. 30, 2022
USD ($)
Sep. 30, 2022
USD ($)
AirCraft
Summary Of Significant Accounting Policies [Line Items]            
Deferred revenue   $ 1.8   $ 1.3    
Lease revenue   $ 32.3 $ 38.7 $ 111.4 $ 118.5  
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]   Revenue From Contract With Customer Excluding Assessed Tax Revenue From Contract With Customer Excluding Assessed Tax      
Number of air craft leased from third parties | AirCraft       18    
Current and non-current deferred credit contract liability balances $ 4.9 $ 4.9   $ 4.9   $ 3.9
Recognized deferred credits within contract revenue   0.1 $ 0.2 1.6 0.6  
Amortization of heavy maintenance and major overhaul costs charged to depreciation and amortization expense   0.8 0.5 2.3 1.2  
Deferred heavy maintenance balance, net of accumulated amortization $ 8.8 8.8   8.8   $ 9.7
Engine overhaul expense   11.5 8.1 28.2 18.2  
Engine overhaul pass-through expense   11.3 6.0 27.9 14.5  
Airframe check expense   3.8 5.0 12.6 18.8  
Airframe check pass-through expense   $ 2.4 $ 1.3 $ 8.6 $ 1.7  
CRJ 700 [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Number of aircraft to be leased | AirCraft       20   20
Operating lease, term of contract 9 years 9 years   9 years    
CRJ 700 [Member] | GoJet Agreements [Member]            
Summary Of Significant Accounting Policies [Line Items]            
Number of aircraft classified as assets held for sale | AirCraft           18
Number of aircraft sold | AirCraft 18