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	3 Months Ended		9 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2015	May. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance	$ 121,070	$ 140,631	$ 114,917	$ 134,134
Balance	109,220	130,159	109,220	130,159
Cost of Goods, Total
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total gains or losses included in cost of goods sold and net interest	$ (11,850)	$ (10,472)	$ (5,697)	$ (3,975)