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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 12 Months Ended
Aug. 31, 2021
Aug. 31, 2020
Aug. 31, 2019
Sep. 01, 2021
Sep. 01, 2020
Nov. 30, 2019
Sep. 01, 2019
Sep. 01, 2018
Aug. 31, 2018
Aug. 02, 2018
Jun. 01, 2017
Summary Of Significant Accounting Policies [Line Items]                      
Net foreign currency translation adjustment $ 35,800,000 $ 39,800,000 $ 34,200,000                
Allowance for doubtful accounts $ 2,408,000 2,670,000 2,176,000           $ 2,701,000    
Property, Plant and Equipment useful life 40 years                    
Impairment of long-lived assets $ 0 0 0                
Research and development 6,300,000 5,800,000 5,400,000                
Stock based compensation expense 14,704,000 8,997,000 $ 11,153,000                
Increase (decrease) to retained earnings 881,740,000 885,460,000                  
Operating lease right of use asset 39,819,000 62,389,000                  
Operating lease liability 42,568,000 64,509,000                  
Decrease in Additional paid in capital $ 469,721,000 $ 460,400,000                  
Accounting Standards Update 2014-09                      
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                    
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, Immaterial Effect [true false] true                    
Change in Accounting Principle, Accounting Standards Update, Adoption Date Sep. 01, 2019                    
Operating lease right of use asset             $ 40,400,000        
Operating lease liability             41,600,000        
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 2016-13                      
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, 2020                    
Accounting Standards Update 2020-06 | Subsequent Events                      
Summary Of Significant Accounting Policies [Line Items]                      
Increase (decrease) to retained earnings       $ (3,000,000)              
Decrease in Additional paid in capital       (51,000,000)              
Derecognition of deferred tax liabilities       17,000,000              
Increase in convertible note due to due to separation of debt & equity       $ 71,000,000              
Cumulative Effect Adjustment Due to Adoption | Accounting Standards Update 2014-09                      
Summary Of Significant Accounting Policies [Line Items]                      
Increase (decrease) to retained earnings               $ 5,500,000      
Cumulative Effect Adjustment Due to Adoption | Accounting Standards Update 2016-02 | Deferred Gains Recognised as Earnings                      
Summary Of Significant Accounting Policies [Line Items]                      
Increase (decrease) to retained earnings             $ 4,400,000        
Cumulative Effect Adjustment Due to Adoption | ASU 2016-13                      
Summary Of Significant Accounting Policies [Line Items]                      
Increase (decrease) to retained earnings         $ (500,000)            
2.875% Convertible senior notes, due 2024                      
Summary Of Significant Accounting Policies [Line Items]                      
Debt instrument, interest rate 2.875% 2.875% 2.875%                
2.25% Convertible senior notes, due 2024                      
Summary Of Significant Accounting Policies [Line Items]                      
Debt instrument, interest rate 2.25% 2.25% 2.25%                
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%   24.50%     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%