Fair Value Measurements - Fair Value Reconciliation Liabilities Using Significant Unobservable Inputs (Level 3) (Details) (Accrued liability for contingent crack spread payments related to purchase of noncontroling interests, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Aug. 31, 2013	Aug. 31, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - beginning	$ 127,516
Purchases		105,188
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	(16,491)
Balance - ending	134,134	127,516
Cost of Goods, Total
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Total gains included in cost of goods sold and net interest	$ 23,109	$ 22,328