Lease Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Aug. 31, 2012	Aug. 31, 2011	Aug. 31, 2010
Railcar Equipment
Leases Disclosure [Line Items]
Lease expense	$ 6.0	$ 6.5	$ 8.2
Domestic railcar repair facilities, office space and certain manufacturing and office equipment
Leases Disclosure [Line Items]
Lease expense	$ 14.1	$ 12.2	$ 12.4

Rental expense incurred for leased assets including furniture and equipment which has not been recognized in costs and expenses applicable to sales and revenues; for example, cost of goods sold or other operating costs and expenses.

No definition available.

Name:	us-gaap_LeaseAndRentalExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration