Investments - Narrative (Details) (USD $)	9 Months Ended		3 Months Ended			9 Months Ended		9 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2014 Ardent Mills [Member]	May 31, 2014 Horizon Milling, LLC [Member]	May 31, 2014 Ventura Foods, LLC	May 31, 2014 National Cooperative Refinery Association [Member]	Aug. 31, 2013 National Cooperative Refinery Association [Member]	May 31, 2014 Energy [Member] National Cooperative Refinery Association [Member]	May 31, 2013 Energy [Member] National Cooperative Refinery Association [Member]	May 31, 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]	May 31, 2013 Fair Value, Inputs, Level 3 [Member] Fair Value, Measurements, Recurring [Member] National Cooperative Refinery Association [Member]
Schedule of Equity Method Investments [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage						84.00%	79.20%
Payments to Acquire Business, Contingent Consideration Paid						$ (16,500,000)
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								130,159,000		130,159,000	134,134,000	146,245,000
Ownership percentage					50.00%
Equity Method Investment, Additional Cash Contribution				32,800,000
Investments redeemed			123,500,000
Gain (Loss) on Sale of Investments				108,800,000
Equity value exceeding carrying value					$ 12,900,000