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Summary of Significant Accounting Policies - Additional Information (Detail)
 1 Months Ended 3 Months Ended 6 Months Ended
Apr. 23, 2021
USD ($)
Apr. 15, 2021
USD ($)
Apr. 30, 2021
USD ($)
Mar. 31, 2021
USD ($)
Air-craft
Feb. 28, 2021
USD ($)
Mar. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Mar. 31, 2020
USD ($)
Mar. 31, 2021
USD ($)
Air-craft
Mar. 31, 2020
USD ($)
Sep. 30, 2020
USD ($)
Summary Of Significant Accounting Policies [Line Items]                      
Number of aircrafts operated | Air-craft                 163    
Lease incentive assets       $ 4,800,000   $ 4,800,000     $ 4,800,000    
Lease incentive obligations       4,200,000   4,200,000     4,200,000    
Deferred revenue           4,900,000          
Lease termination expense       4,500,000              
Current and non-current deferred credit balances       5,200,000   5,200,000     5,200,000   $ 8,500,000
Recognized deferred credits within contract revenue           1,100,000   $ 1,900,000 900,000 $ 2,000,000.0  
Deferred heavy maintenance balance, net of accumulated amortization       $ 1,200,000   1,200,000     1,200,000   $ 0
Engine overhaul expense           6,900,000   14,500,000 21,300,000 25,100,000  
Engine overhaul pass-through expense           2,200,000   700,000 11,800,000 2,600,000  
Airframe check expense           14,100,000   10,500,000 24,200,000 17,800,000  
Airframe check pass-through expense           5,600,000   3,900,000 12,700,000 5,100,000  
Payroll Support Program Extension, amount granted         $ 48,700,000            
Payroll Support Program Extension, additional amount granted         7,300,000            
Payroll Support Program Extension, total amount granted         $ 56,000,000.0            
Payroll support government funds           $ 56,000,000.0     67,300,000    
deferred payments             $ 11,300,000   $ 0    
Subsequent Event [Member]                      
Summary Of Significant Accounting Policies [Line Items]                      
Payroll Support Program Extension, additional amount granted     $ 7,300,000                
Third Payroll Support Program, eligible and estimated amount   $ 52,200,000                  
Third Payroll Support Program, amount received $ 26,100,000                    
Aircraft [Member]                      
Summary Of Significant Accounting Policies [Line Items]                      
Percentage leased                 10.00%    
CRJ 700 [Member]                      
Summary Of Significant Accounting Policies [Line Items]                      
Number of aircraft to be leased | Air-craft       6              
Number of aircrafts operated | Air-craft       20              
Operating lease, term of contract       9 years   9 years     9 years    
Contract Revenue [Member]                      
Summary Of Significant Accounting Policies [Line Items]                      
Lease revenue           $ 18,100,000   $ 52,400,000 $ 67,600,000 $ 105,700,000