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Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) (Fair Value, Inputs, Level 3, Accrued liability for contingent crack spread payments related to purchase of noncontroling interests, USD $)
 12 Months Ended
Aug. 31, 2014
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Contractual target crack spread margin (in dollars per share) $ 17.50 [1]
Expected volatility 132.37% [2]
Minimum
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement $ 13.58 [3]
Risk-free interest rate 0.09% [4]
Expected life (years) 1 year 0 months [5]
Average
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement 15.64 [3]
Risk-free interest rate 0.53% [4]
Expected life (years) 2 years 0 months 7 days [5]
Maximum
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Fair Value Inputs, Forward Crack Spread Margin Quotes and Management Estimates Based on Future Settlement 17.07 [3]
Risk-free interest rate 0.94% [4]
Expected life (years) 3 years 0 months [5]
Fair Value, Measurements, Recurring
  
Fair Value Inputs, Assets, Quantitative Information [Line Items]  
Accrued liability for contingent crack spread payments related to purchase of noncontrolling interest $ 114,917,000
[1] Represents the minimum contractual threshold that would require settlement with the counterparties
[2] Represents quarterly adjusted volatility estimates derived from daily historical market data
[3] Represents forward crack spread margin quotes and management estimates based on future settlement dates
[4] Represents yield curves for U.S. Treasury securities
[5] Represents the range in the number of years remaining related to each contingent payment