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, 2014	Aug. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance - beginning	$ 134,134	$ 127,516
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	0	(16,491)
Balance - ending	114,917	134,134
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	$ (19,217)	$ 23,109

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, 2014

Aug. 31, 2013

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]

Balance - beginning

$ 134,134

$ 127,516

Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3

(16,491)

Balance - ending

114,917

134,134

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

$ (19,217)

$ 23,109