Investments - Narrative (Details) (USD $) In Millions, unless otherwise specified						6 Months Ended
	Feb. 28, 2013	Feb. 28, 2013 Horizon Milling, LLC [Member]	Feb. 28, 2013 Ventura Foods, LLC	Feb. 28, 2013 National Cooperative Refinery Association [Member]	Aug. 31, 2012 National Cooperative Refinery Association [Member]	Feb. 28, 2013 Growmark [Member] National Cooperative Refinery Association [Member]	Feb. 28, 2013 MFA [Member] National Cooperative Refinery Association [Member]
Schedule of Equity Method Investments [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage					74.50%
Business Combination, Step Acquisition, Amount						$ 48.0	$ 18.0
Business Combination, Step Acquisition, First Closing, Equity Interest in Acquiree, Percentage				79.20%
Ownership percentage		24.00%	50.00%
Expected ownership of future joint venture	0.00%
Equity value exceeding carrying value			$ 12.9