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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 12 Months Ended
Aug. 31, 2022
Aug. 31, 2021
Aug. 31, 2020
Sep. 01, 2021
Sep. 01, 2020
Sep. 01, 2019
Aug. 31, 2019
Aug. 02, 2018
Jun. 01, 2017
Summary Of Significant Accounting Policies [Line Items]                  
Net foreign currency translation adjustment $ 57,400,000 $ 35,800,000 $ 39,800,000            
Allowance for doubtful accounts $ 2,300,000 2,400,000 2,700,000       $ 2,200,000    
Property, Plant and Equipment useful life 40 years                
Impairment of long-lived assets $ 0 0 0            
Research and development 5,400,000 6,300,000 5,800,000            
Stock based compensation expense 15,500,000 14,700,000 $ 9,000,000.0            
Increase in retained earnings 897,700,000 881,700,000              
Reduction to additional paid in capital $ 424,800,000 $ 469,700,000              
Accounting Standards Update 2016-02                  
Summary Of Significant Accounting Policies [Line Items]                  
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] true                
Change in Accounting Principle, Accounting Standards Update, Adoption Date Sep. 01, 2019                
Accounting Standards Update 2017-12                  
Summary Of Significant Accounting Policies [Line Items]                  
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] true                
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false] true                
Change in Accounting Principle, Accounting Standards Update, Adoption Date Sep. 01, 2019                
ASU 2020-06                  
Summary Of Significant Accounting Policies [Line Items]                  
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] true                
Change in Accounting Principle, Accounting Standards Update, Adoption Date Sep. 01, 2021                
ASU 2019-12                  
Summary Of Significant Accounting Policies [Line Items]                  
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] true                
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false] true                
Change in Accounting Principle, Accounting Standards Update, Adoption Date Sep. 01, 2021                
ASU 2020-04                  
Summary Of Significant Accounting Policies [Line Items]                  
Change in Accounting Principle, Accounting Standards Update, Adopted [true false] true                
Change in Accounting Principle, Accounting Standards Update, Adoption Date Aug. 31, 2022                
Cumulative Effect Adjustment Due to Adoption | Accounting Standards Update 2016-02                  
Summary Of Significant Accounting Policies [Line Items]                  
Increase in retained earnings           $ 4,400,000      
Cumulative Effect Adjustment Due to Adoption | ASU 2016-13                  
Summary Of Significant Accounting Policies [Line Items]                  
Increase in retained earnings         $ (500,000)        
Cumulative Effect Adjustment Due to Adoption | ASU 2020-06                  
Summary Of Significant Accounting Policies [Line Items]                  
Increase in retained earnings       $ 5,000,000          
Reduction to additional paid in capital       (59,000,000)          
Derecognition of deferred tax liabilities       17,000,000          
Increase in convertible note due to derecognition of debt discount       $ 71,000,000          
2.875% Convertible senior notes, due 2024                  
Summary Of Significant Accounting Policies [Line Items]                  
Debt instrument, interest rate 2.875% 2.875% 2.875%            
2.875% Convertible senior notes, due 2028                  
Summary Of Significant Accounting Policies [Line Items]                  
Debt instrument, interest rate 2.875% 2.875%              
Customer Relationships | Maximum                  
Summary Of Significant Accounting Policies [Line Items]                  
Estimated useful lives 20 years                
GIMSA                  
Summary Of Significant Accounting Policies [Line Items]                  
Interest in joint venture 50.00%                
Greenbrier-Astra Rail                  
Summary Of Significant Accounting Policies [Line Items]                  
Ownership percentage by parent                 75.00%
Rayvag                  
Summary Of Significant Accounting Policies [Line Items]                  
Interest in joint venture               68.00%  
Greenbrier-Maxion                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of ownership in entity 60.00%                
Amsted-Maxion Cruzeiro                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of ownership in entity 29.50%                
Amsted-Maxion Cruzeiro | Greenbrier-Maxion                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of ownership in entity 40.00%                
Greenbrier Railcar Funding I LLC                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of ownership in entity 40.00%                
Axis LLC                  
Summary Of Significant Accounting Policies [Line Items]                  
Percentage of ownership in entity 41.90%