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	Nov. 30, 2012	Aug. 31, 2012	Nov. 30, 2011
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 635,684	$ 1,071,778	$ 641,905
Derivative Liabilities	525,094	730,878	541,021
Commodity and freight derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	632,544	1,070,800	641,890
Derivative Liabilities	518,377	727,946	540,426
Foreign exchange derivatives
Derivatives, Fair Value [Line Items]
Derivative Assets	3,140	978	15
Derivative Liabilities	6,234	2,388
Interest rate derivatives
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 483	$ 544	$ 595