Investments - Narrative (Details) (USD $)	6 Months Ended				6 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014 Horizon Milling, LLC [Member]	Feb. 28, 2014 Ventura Foods, LLC	Feb. 28, 2014 Energy [Member] National Cooperative Refinery Association [Member]	Feb. 28, 2013 Energy [Member] National Cooperative Refinery Association [Member]	Feb. 28, 2014 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] National Cooperative Refinery Association [Member]	Aug. 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] National Cooperative Refinery Association [Member]	Feb. 28, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] National Cooperative Refinery Association [Member]
Schedule of Equity Method Investments [Line Items]
Payments for Repurchase of Redeemable Noncontrolling Interest	$ 65,981,000	$ 65,981,000			$ 66,000,000	$ (66,000,000)
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest					140,631,000		140,631,000	134,134,000	140,987,000
Ownership percentage			24.00%	50.00%
Expected ownership of future joint venture	0.00%
Expected borrowings of future joint venture	600,000,000
Equity value exceeding carrying value				$ 12,900,000