Revolving Notes - Additional Information (Detail)	6 Months Ended
	Feb. 29, 2020 USD ($) Facility CreditFacility	Aug. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 451,100,000
Long-term Line of Credit	$ 37,196,000	$ 27,115,000
Number of lines of credits | CreditFacility	2
Senior Secured Credit Facilities, Consisting of 3 Components
Line of Credit Facility [Line Items]
Number of senior secured credit facilities | Facility	3
Line of credit facility maximum capacity	$ 706,000,000.0
Letter of credit facility outstanding amount	27,500,000	24,400,000
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	2024-06
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%
European Line of Credit, 2nd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 56,000,000.0
Long-term Line of Credit	14,000,000.0
Letter of credit facility outstanding amount	$ 37,200,000	$ 27,100,000
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Minimum
Line of Credit Facility [Line Items]
Line of credit maturity date	2020-06
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Maximum
Line of Credit Facility [Line Items]
Line of credit maturity date	2021-07
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	1.10%
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 Joint Venture Line of Credit, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 50,000,000
Mexican Railcar Manufacturing Joint Venture 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
Line of credit facility borrowings outstanding due period	2024-03
Mexican Railcar Manufacturing Joint Venture Line of Credit 1, 3rd Component of Senior Secured Credit Facilities | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	2.00%
Mexican Railcar Manufacturing Joint Venture Line of Credit 2, 3rd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 20,000,000
Line of credit facility borrowings outstanding due period	2021-06
Joint venture partner each guaranteed percentage	50.00%
Mexican Railcar Manufacturing Joint Venture 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	2.00%