Fair Value Measurements - Fair Value Measurements (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Aug. 31, 2012	Aug. 31, 2011
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure
Foreign currency derivatives	957	1,508
Other assets	75,000	68,246
Total assets	146,543	154,836
Foreign currency derivatives	2,366
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest
Total liabilities	152,415	191,607
Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity and feight derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity and freight derivatives, assets	70,586	85,082
Derivative liabilities	150,049	191,607
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest rate swap derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure	1,702,757	1,288,049
Foreign currency derivatives
Other assets
Total assets	2,481,119	1,837,105
Foreign currency derivatives
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest
Total liabilities	356,590	291,006
Significant Other Observable Inputs (Level 2) | Commodity and feight derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity and freight derivatives, assets	778,362	549,056
Derivative liabilities	356,046	290,256
Significant Other Observable Inputs (Level 2) | Interest rate swap derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	544	750
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure
Foreign currency derivatives
Other assets
Total assets
Foreign currency derivatives
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	127,516
Total liabilities	127,516
Significant Unobservable Inputs (Level 3) | Commodity and feight derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity and freight derivatives, assets
Derivative liabilities
Significant Unobservable Inputs (Level 3) | Interest rate swap derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure	1,702,757	1,288,049
Foreign currency derivatives	957	1,508
Other assets	75,000	68,246
Total assets	2,627,662	1,991,941
Foreign currency derivatives	2,366
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	127,516
Total liabilities	636,521	482,613
Estimate of Fair Value, Fair Value Disclosure [Member] | Commodity and feight derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity and freight derivatives, assets	848,948	634,138
Derivative liabilities	506,095	481,863
Estimate of Fair Value, Fair Value Disclosure [Member] | Interest rate swap derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	$ 544	$ 750