Revolving Notes - Additional Information (Detail)	12 Months Ended
	Aug. 31, 2023 USD ($) CreditFacility Facility	Aug. 31, 2022 USD ($)
Line of Credit Facility [Line Items]
Long-term line of credit	$ 297,100,000	$ 296,600,000
European
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	72,800,000
Long-term line of credit	$ 35,900,000
Mexican
Line of Credit Facility [Line Items]
Number of lines of credits | CreditFacility	3
Minimum | European
Line of Credit Facility [Line Items]
Line of credit maturity date	2023-10
Maximum | European
Line of Credit Facility [Line Items]
Line of credit maturity date	2025-07
WIBOR | Minimum | European
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.20%
WIBOR | Maximum | European
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.60%
EURIBOR | Minimum | European
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.50%
EURIBOR | Maximum | European
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.90%
Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Number of senior secured credit facilities | Facility	4
Line of credit facility maximum capacity	$ 1,400,000,000
Letter of credit facility outstanding amount	4,900,000	6,900,000
Senior Secured Credit Facilities | North American
Line of Credit Facility [Line Items]
Long-term line of credit		160,000,000.0
Senior Secured Credit Facilities | European
Line of Credit Facility [Line Items]
Long-term line of credit	47,200,000	51,600,000
Senior Secured Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Long-term line of credit	110,000,000.0	$ 85,000,000.0
Committed Credit Facilities
Line of Credit Facility [Line Items]
Aggregate amount available to draw down	364,400,000
Committed Credit Facilities | North American
Line of Credit Facility [Line Items]
Aggregate amount available to draw down	273,800,000
Committed Credit Facilities | European
Line of Credit Facility [Line Items]
Aggregate amount available to draw down	25,600,000
Committed Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Aggregate amount available to draw down	0
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | North American
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 600,000,000
Line of credit maturity date	2026-08
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | Prime Rate | North American
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	0.50%
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | SOFR | North American
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.50%
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | SOFR Adjustment | North American
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	0.10%
GBX Leasing
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 550,000,000
Line of credit maturity date	2027-08
Long-term line of credit	$ 139,900,000
GBX Leasing | Interest rate swap contracts
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	87.00%
GBX Leasing | SOFR
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	1.85%
GBX Leasing | SOFR Adjustment
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	0.11%
Mexican Railcar Manufacturing Joint Venture Line of Credit, 3rd Component of Senior Secured Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 175,000,000
Mexican Railcar Manufacturing Operations Line of Credit 1, 3rd Component of Senior Secured Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 100,000,000
Line of credit facility borrowings outstanding due period	2026-06
Mexican Railcar Manufacturing Operations Line of Credit 1, 3rd Component of Senior Secured Credit Facilities | LIBOR | Mexican
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	4.25%
Mexican Railcar Manufacturing Operations Line of Credit 2, 3rd Component of Senior Secured Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 45,000,000
Line of credit facility borrowings outstanding due period	2025-02
Joint venture partner each guaranteed percentage	50.00%
Mexican Railcar Manufacturing Operations Line of Credit 2, 3rd Component of Senior Secured Credit Facilities | SOFR | Mexican
Line of Credit Facility [Line Items]
Debt instrument, percentage of debt principal balance hedged	2.55%
Mexican Railcar Manufacturing Operations Line of Credit 3, 3rd Component of Senior Secured Credit Facilities | Mexican
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 30,000,000
Line of credit facility borrowings outstanding due period	2024-06
Joint venture partner each guaranteed percentage	50.00%