Fair Value Measurements - Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2015	Aug. 31, 2014
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure	$ 1,246,484	$ 921,554
Deferred Compensation Assets, Fair Value Disclosure	84,479	83,217
Other Assets, Fair Value Disclosure	11,013	8,778
Total assets	1,955,980	1,617,482
Foreign Currency Contracts, Liability, Fair Value Disclosure	13,215	2,248
Total liabilities	603,660	714,907
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	5,620	2,523
Fair Value, Measurements, Recurring [Member] | Commodity and Freight Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	595,994	597,210
Derivative Liability	464,985	597,612
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	12,390	4,200
Derivative Liability	4,390	130
Fair Value, Measurements, Recurring [Member] | 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	0	0
Deferred Compensation Assets, Fair Value Disclosure	84,479	83,217
Other Assets, Fair Value Disclosure	11,013	8,778
Total assets	227,527	173,108
Foreign Currency Contracts, Liability, Fair Value Disclosure	13,215	2,248
Total liabilities	170,995	119,938
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	5,620	2,523
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity and Freight Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	126,415	78,590
Derivative Liability	157,780	117,690
Fair Value, Measurements, Recurring [Member] | 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 Asset	0	0
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure	1,246,484	921,554
Deferred Compensation Assets, Fair Value Disclosure	0	0
Other Assets, Fair Value Disclosure	0	0
Total assets	1,728,453	1,444,374
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Total liabilities	311,595	480,052
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Commodity and Freight Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	469,579	518,620
Derivative Liability	307,205	479,922
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	12,390	4,200
Derivative Liability	4,390	130
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure	0	0
Deferred Compensation Assets, Fair Value Disclosure	0	0
Other Assets, Fair Value Disclosure	0	0
Total assets	0	0
Foreign Currency Contracts, Liability, Fair Value Disclosure	0	0
Total liabilities	121,070	114,917
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign Currency Contract, Asset, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity and Freight Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset	0	0
Derivative Liability	0	0
NCRA [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest		114,917
NCRA [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	0	0
NCRA [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	0	0
NCRA [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	121,070	114,917
National Cooperative Refinery Association [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest	$ 121,070