Fair Value Measurements - Fair Value Reconciliation Liabilities Using Significant Unobservable Inputs (3 month) (Level 3) (Details) (National Cooperative Refinery Association [Member], Crack Spread Contingent Payment [Member], USD $) In Thousands, unless otherwise specified							3 Months Ended		9 Months Ended
	May 31, 2014	Feb. 28, 2014	Aug. 31, 2013	May 31, 2013	Feb. 28, 2013	Aug. 31, 2012	May 31, 2014 Cost of Goods, Total	May 31, 2013 Cost of Goods, Total	May 31, 2014 Cost of Goods, Total	May 31, 2013 Cost of Goods, Total
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	$ 130,159	$ 140,631	$ 134,134	$ 146,245	$ 140,987	$ 127,516
Total gains or losses included in cost of goods sold and net interest							(10,472)	5,258	(3,975)	18,729
Balance	$ 130,159	$ 140,631	$ 134,134	$ 146,245	$ 140,987	$ 127,516