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%

GREENBRIER COMPANIES INC 10-K