Revolving Notes - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Mar. 31, 2014	Aug. 31, 2018 USD ($) Facility CreditFacility	Aug. 31, 2017 USD ($)
LIBOR
Line of Credit Facility [Line Items]
Debt instrument, percentage points added to the reference rate	1.75%
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		$ 635,300,000
Letter of credit facility outstanding amount		72,200,000	$ 77,600,000
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		$ 35,300,000
Letter of credit facility outstanding amount		$ 27,700,000	$ 4,300,000
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Minimum
Line of Credit Facility [Line Items]
Line of credit maturity date		2018-10
European Line of Credit, 2nd Component of Senior Secured Credit Facilities | Maximum
Line of Credit Facility [Line Items]
Line of credit maturity date		2019-06
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%
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
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		2019-07
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%