Summary of Significant Accounting Policies - Derivative Assets and Liabilities Not Designated As Hedging Instruments (Details) (Not Designated as Hedging Instrument, USD $) In Thousands, unless otherwise specified	Aug. 31, 2012	Aug. 31, 2011
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 1,071,778	$ 883,953
Derivative Liabilities	730,878	730,920
Commodity and freight derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	1,070,800	882,445
Derivative Liabilities	727,946	730,170
Foreign exchange derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	978	1,508
Derivative Liabilities	2,388
Interest rate derivatives
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 544	$ 750