Fair Value Measurements - Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Feb. 28, 2014	Aug. 31, 2013	Feb. 28, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 621,523	$ 499,890	$ 501,178
Derivative Liability, Fair Value, Gross Liability	553,693	465,066	429,975
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
Other Assets, Fair Value Disclosure	114,261	114,084	79,333
Total assets	178,244	179,419	133,157
Total liabilities	93,618	65,109	21,775
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	1,318,428	1,203,383	1,697,214
Other Assets, Fair Value Disclosure
Total assets	1,875,968	1,637,940	2,144,568
Total liabilities	460,075	399,958	408,200
Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory, Current, Fair Value Disclosure
Other Assets, Fair Value Disclosure
Total assets
Total liabilities	140,631	134,134	140,987
Fair Value, Measurements, Recurring [Member] \| 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	1,318,428	1,203,383	1,697,214
Other Assets, Fair Value Disclosure	114,261	114,084	79,333
Total assets	2,054,212	1,817,359	2,277,725
Total liabilities	694,324	599,201	570,962
Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	6,345	7,079	15,497
Derivative Liability, Fair Value, Gross Liability	2,629	5,925	691
Foreign Exchange Contract [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]
Derivative Asset, Fair Value, Gross Asset	6,345	6,894	15,497
Derivative Liability, Fair Value, Gross Liability	2,629	5,925	691
Foreign Exchange Contract [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]
Derivative Asset, Fair Value, Gross Asset		185
Derivative Liability, Fair Value, Gross Liability
Foreign Exchange Contract [Member] \| Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset
Derivative Liability, Fair Value, Gross Liability
Foreign Exchange Contract [Member] \| Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	6,345	7,079	15,497
Derivative Liability, Fair Value, Gross Liability	2,629	5,925	691
Commodity and Freight Derivatives [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	615,178	468,673	485,222
Derivative Liability, Fair Value, Gross Liability	550,870	458,893	428,866
Commodity and Freight Derivatives [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]
Derivative Asset, Fair Value, Gross Asset	57,638	58,441	38,327
Derivative Liability, Fair Value, Gross Liability	90,989	59,184	21,084
Commodity and Freight Derivatives [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]
Derivative Asset, Fair Value, Gross Asset	557,540	410,233	446,895
Derivative Liability, Fair Value, Gross Liability	459,881	399,710	407,782
Commodity and Freight Derivatives [Member] \| Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset
Derivative Liability, Fair Value, Gross Liability
Commodity and Freight Derivatives [Member] \| Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset	615,178	468,674	485,222
Derivative Liability, Fair Value, Gross Liability	550,870	458,894	428,866
Interest Rate Swap [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]
Derivative Asset, Fair Value, Gross Asset
Derivative Liability, Fair Value, Gross Liability
Interest Rate Swap [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]
Derivative Asset, Fair Value, Gross Asset		24,139	459
Derivative Liability, Fair Value, Gross Liability	194	248	418
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset
Derivative Liability, Fair Value, Gross Liability
Interest Rate Swap [Member] \| Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Asset, Fair Value, Gross Asset		24,139	459
Derivative Liability, Fair Value, Gross Liability	194	248	418
National Cooperative Refinery Association [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
National Cooperative Refinery Association [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
National Cooperative Refinery Association [Member] \| Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3)
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	140,631	134,134	140,987
National Cooperative Refinery Association [Member] \| Fair Value, Measurements, Recurring [Member] \| Estimate of Fair Value, Fair Value Disclosure [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		$ 134,134	$ 140,987