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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Aug. 31, 2024 | Aug. 31, 2023 | Aug. 31, 2022 | Sep. 01, 2021 | Aug. 31, 2021 | Jun. 01, 2017
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Allowance for doubtful accounts | $ 3,600,000 | $ 2,800,000 | $ 2,300,000 |  | $ 2,400,000 |
Equipment on operating leases useful life | 40 years |  |  |  |  |
Impairment of long-lived assets | $ 0 | $ 24,200,000 | $ 0 |  |  |
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 | $ 5,200,000 | $ 4,000,000 | $ 5,400,000 |  |  |
Goodwill impairment | 0 | 0 | 0 |  |  |
Contingently redeemable noncontrolling interest | 41,700,000 | 55,600,000 |  |  |  |
Noncash redemption value of noncontrolling interest | 16,200,000 | 26,300,000 |  |  |  |
Stock based compensation expense | 17,100,000 | 12,100,000 | $ 15,500,000 |  |  |
Increase in retained earnings | 1,035,000,000 | 897,500,000 |  |  |  |
Reduction to additional paid in capital | $ 375,100,000 | $ 364,400,000 |  |  |  |
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 |  |  |  |  |
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% | 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% |  |  |  |  |

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