Fair Value Measurements - Fair Value Measurements (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Feb. 28, 2013	Aug. 31, 2012	Feb. 29, 2012
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 Contract, Asset, Fair Value Disclosure	15,497	957
Other assets	79,333	75,000	74,537
Total assets	124,176	146,543	91,580
Foreign currency derivatives	969	2,366	72
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest
Total liabilities	16,630	152,415	52,047
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	29,346	70,586	17,043
Derivative liabilities	15,661	150,049	51,975
Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest Rate Swap [Member]
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	1,697,214	1,702,757	1,406,976
Foreign Currency Contract, Asset, Fair Value Disclosure
Other assets
Total assets	1,940,844	2,481,119	1,598,202
Foreign currency derivatives
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest
Total liabilities	200,640	356,590	244,195
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	243,171	778,362	191,226
Derivative liabilities	200,222	356,046	243,609
Significant Other Observable Inputs (Level 2) | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets - Interest Rate Swaps	459
Derivative liabilities	418	544	586
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 Contract, Asset, Fair Value Disclosure
Other assets
Total assets
Foreign currency derivatives
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	140,987	127,516	101,003
Total liabilities	140,987	127,516	101,003
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 [Member]
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	1,697,214	1,702,757	1,406,976
Foreign Currency Contract, Asset, Fair Value Disclosure	15,497	957
Other assets	79,333	75,000	74,537
Total assets	2,065,020	2,627,662	1,689,782
Foreign currency derivatives	969	2,366	72
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	140,987	127,516	101,003
Total liabilities	358,257	636,521	397,245
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	272,517	848,948	208,269
Derivative liabilities	215,883	506,095	295,584
Estimate of Fair Value, Fair Value Disclosure [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets - Interest Rate Swaps	459
Derivative liabilities	$ 418	$ 544	$ 586