Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Aug. 31, 2023	Aug. 31, 2022	Aug. 31, 2021	Sep. 01, 2021	Sep. 01, 2020	Aug. 31, 2020	Jun. 01, 2017
Summary Of Significant Accounting Policies [Line Items]
Allowance for doubtful accounts	$ 2,800,000	$ 2,300,000	$ 2,400,000			$ 2,700,000
Equipment on operating leases useful life	40 years
Impairment of long-lived assets	$ 24,200,000	$ 0	$ 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	$ 4,000,000	$ 5,400,000	$ 6,300,000
Goodwill impairment	0	0	0
Contingently redeemable noncontrolling interest	55,600,000	27,700,000
Noncash redemption value of noncontrolling interest	26,300,000
Stock based compensation expense	12,100,000	15,500,000	$ 14,700,000
Increase in retained earnings	897,500,000	897,700,000
Reduction to additional paid in capital	$ 364,400,000	$ 424,800,000
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 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%	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%
Axis LLC
Summary Of Significant Accounting Policies [Line Items]
Percentage of ownership in entity	41.90%