Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended					12 Months Ended	1 Months Ended			12 Months Ended				12 Months Ended
	Aug. 31, 2012 Vehicle	May 31, 2012 Vehicle	Aug. 31, 2011	Aug. 31, 2012 Reduction in revenue on the sale of new railcars Vehicle	Aug. 31, 2012 Reduction in gain on sale of used railcars Vehicle	Aug. 31, 2012 Seb Finans Ab Vehicle	Mar. 31, 2004 Okombi GmbH	Aug. 31, 2012 Okombi GmbH Vehicle	Jan. 31, 2000 Okombi GmbH Vehicle	Aug. 31, 2012 Mexican Joint Venture Credit Facility	Aug. 31, 2012 Minimum Y	Aug. 31, 2012 Maximum Y	May 31, 2012 Maximum	Aug. 31, 2012 Additional Investigation Year	Aug. 31, 2012 Portland Harbor Site Minimum	Aug. 31, 2012 Portland Harbor Site Maximum	Aug. 31, 2012 Area Of Willamette River Adjacent to the Company's Portland, Oregon Manufacturing Facility Minimum	Aug. 31, 2012 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	$ 90
Remedial investigation and feasibility study, period	11 years													2 years
Period for remedial action											2	28
Cleanup expenses															169	1,800	9	163
Number of installed railcar						372
Value of railcars	61.1					20.0
Settlement agreement effective date						2007-02-28	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	2.3
Number of railcars sold	743	743		600	143
Maximum potential obligation												4.2	4.2
Obligation to deliver railcar expiration date	2033-03
Debt outstanding										45.6
Guarantee obligations										37.8
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 for capital expenditure of fourth manufacturing line										1.4
Outstanding letters of credit	$ 5.6		$ 4.3