Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended		1 Months Ended			9 Months Ended
	May 31, 2013	Nov. 30, 2012	May 31, 2012	May 31, 2013 Mexican Joint Venture Credit Facility	May 31, 2013 Seb Finans Ab Vehicle	Mar. 31, 2004 Okombi GmbH	May 31, 2013 Okombi GmbH Vehicle	Jan. 31, 2000 Okombi GmbH Vehicle	May 31, 2013 Minimum Y	May 31, 2013 Maximum Y	May 31, 2013 Additional Investigation Year	May 31, 2013 Portland Harbor Site Minimum	May 31, 2013 Portland Harbor Site Maximum	May 31, 2013 Area Of Willamette River Adjacent to the Company's Portland, Oregon Manufacturing Facility Minimum	May 31, 2013 Area Of Willamette River Adjacent to the Company's Portland, Oregon Manufacturing Facility Maximum
Commitments and Contingencies Disclosure [Line Items]
Remedial investigation and feasibility study	$ 100
Remedial investigation and feasibility study, period	13 years										1 year
Period for remedial action									2	28
Cleanup expenses												169	1,800	9	163
Number of installed railcar					372
Value of railcars	99.6	15.9	61.1		20.0
Settlement agreement effective date					February 28, 2007	March 2004
Number of freight cars to build								201
Number of vehicles required to be removed from service							201
Bank and third party warranty guarantee facilities	1.8
Debt outstanding				50.2
Guarantee obligations				40.1
Contribution to Capital expenditure for fourth manufacturing line commitment				10.0
Percentage of commitment Contribution by company towards fourth Manufacturing line				50.00%
Amount contributed by company and the joint venture partner for capital expenditure of fourth manufacturing line				3.9
Outstanding letters of credit	$ 6.8