Revolving Notes - Additional Information (Detail)	6 Months Ended
	Feb. 28, 2017 USD ($) CreditFacility Facility	Aug. 31, 2016 USD ($)
Senior Secured Credit Facilities, Consisting of 3 Components
Line of Credit Facility [Line Items]
Number of senior secured credit facilities | CreditFacility	3
Line of credit facility maximum capacity	$ 615,000,000
Letter of credit facility outstanding amount	79,200,000	$ 81,300,000
Line of credit outstanding amount	0	$ 0
Revolving Line of Credit, 1st Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 550,000,000
Line of credit maturity date	2020-10
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	1.75%
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	0.75%
European Line of Credit, 2nd Component of Senior Secured Credit Facilities
Line of Credit Facility [Line Items]
Line of credit facility maximum capacity	$ 15,000,000
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Minimum
Line of Credit Facility [Line Items]
Line of credit maturity date	2017-04
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Maximum
Line of Credit Facility [Line Items]
Line of credit maturity date	2017-06
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	1.30%
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
Number of lines of credits | Facility	2
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	2019-01
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	2017-08
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%