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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 12 Months Ended
Aug. 31, 2025
Aug. 31, 2024
Aug. 31, 2023
Feb. 01, 2024
Aug. 31, 2022
Jun. 01, 2017
Summary Of Significant Accounting Policies [Line Items]            
Allowance for credit losses $ 6,500,000 $ 3,600,000 $ 2,800,000   $ 2,300,000  
Equipment on operating leases useful life 40 years          
Impairment of long-lived assets $ 0 $ 0 $ 24,200,000      
Impairment, Long-Lived Asset, Held-for-Use, Statement of Income or Comprehensive Income [Extensible Enumeration] Asset Impairment Disposal And Exit Costs Net Asset Impairment Disposal And Exit Costs Net Asset Impairment Disposal And Exit Costs Net      
Research and development $ 5,500,000 $ 5,200,000 $ 4,000,000      
Goodwill impairment 0 0 0      
Contingently redeemable noncontrolling interest 35,800,000 41,700,000        
Noncash redemption value of noncontrolling interest 0 16,200,000 26,300,000      
Stock based compensation expense 17,500,000 17,100,000 $ 12,100,000      
Increase in retained earnings $ 1,199,000,000 1,035,000,000        
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 [Extensible Enumeration] us-gaap:AccountingStandardsUpdate202307Member          
Reduction to additional paid in capital $ 364,700,000 $ 375,100,000        
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%    
2.875% Convertible senior notes, due 2028            
Summary Of Significant Accounting Policies [Line Items]            
Debt instrument, interest rate 2.875% 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 B.V.            
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%          
Axis LLC            
Summary Of Significant Accounting Policies [Line Items]            
Percentage of ownership in entity 41.90%