Revolving Notes - Additional Information (Detail)	3 Months Ended
	Nov. 30, 2021 USD ($) Facility CreditFacility	Aug. 31, 2021 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 199,000,000.0
Long-term Line of Credit	$ 516,300,000	$ 372,200,000
Number of lines of credits | CreditFacility	4
Senior Secured Credit Facilities, Consisting of 4 Components
Line of Credit Facility [Line Items]
Number of senior secured credit facilities | Facility	4
Line of credit facility maximum capacity	$ 1,100,000,000
Letter of credit facility outstanding amount	6,700,000	8,400,000
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 600,000,000.0
Line of credit maturity date	2026-08
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	1.50%
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities | Prime Rate
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	0.50%
GBX Leasing Warehouse Facility
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 300,000,000.0
Line of credit maturity date	2025-04
Percentage of ownership in join venture	95.00%
Long-term Line of Credit	$ 293,000,000.0	$ 147,000,000.0
GBX Leasing Warehouse Facility | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	2.00%
European Line of Credit, 2nd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 73,800,000
Long-term Line of Credit	$ 37,400,000
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Minimum
Line of Credit Facility [Line Items]
Line of credit maturity date	2022-06
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Maximum
Line of Credit Facility [Line Items]
Line of credit maturity date	2023-10
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | WIBOR | Minimum
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	1.20%
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | WIBOR | Maximum
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	1.50%
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | EURIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	1.10%
Mexican Railcar Manufacturing Operations Line of Credit, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 120,000,000.0
Mexican Railcar Manufacturing Operations Line of Credit 1, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 30,000,000.0
Joint venture partner each guaranteed percentage	50.00%
Line of credit facility borrowings outstanding due period	2024-06
Mexican Railcar Manufacturing Operations Line of Credit 1, 3rd Component of Senior Secured Credit Facilities | LIBOR | Minimum
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	3.75%
Mexican Railcar Manufacturing Operations Line of Credit 1, 3rd Component of Senior Secured Credit Facilities | LIBOR | Maximum
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	4.25%
Mexican Railcar Manufacturing Operations Line of Credit 2, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 35,000,000.0
Joint venture partner each guaranteed percentage	50.00%
Line of credit facility borrowings outstanding due period	2023-06
Mexican Railcar Manufacturing Operations Line of Credit 2, 3rd Component of Senior Secured Credit Facilities | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	3.70%
Mexican Railcar Manufacturing Operations Line of Credit 3, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 50,000,000.0
Line of credit facility borrowings outstanding due period	2024-10
Mexican Railcar Manufacturing Operations Line of Credit 3, 3rd Component of Senior Secured Credit Facilities | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	4.25%
Mexican Railcar Manufacturing Operations Line of Credit 4, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 5,000,000.0
Line of credit facility borrowings outstanding due period	2022-09
Mexican Railcar Manufacturing Operations Line of Credit 4, 3rd Component of Senior Secured Credit Facilities | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	2.95%