Fair Value Measurements and Derivative Instruments - Fair Value of Company's Derivatives by Contract Type (Detail) (USD $)
In Thousands, unless otherwise specified
May 31, 2014
Aug. 31, 2013
Derivatives, Fair Value [Line Items]    
Assets Fair Value $ 303 $ 997
Liabilities Fair Value 3,202 485
Commodity Contract [Member]
   
Derivatives, Fair Value [Line Items]    
Assets Fair Value 303 997
Liabilities Fair Value 3,202 485
Commodity Contract [Member] | Corn futures [Member] | Cash flow hedges [Member] | Designated as Hedging Instrument [Member] | Other current assets [Member]
   
Derivatives, Fair Value [Line Items]    
Assets Fair Value      
Liabilities Fair Value 788 485
Commodity Contract [Member] | Corn futures [Member] | Fair value hedges [Member] | Designated as Hedging Instrument [Member] | Other current assets [Member]
   
Derivatives, Fair Value [Line Items]    
Assets Fair Value 300   
Liabilities Fair Value      
Commodity Contract [Member] | Ethanol futures [Member] | Cash flow hedges [Member] | Designated as Hedging Instrument [Member] | Other current assets [Member]
   
Derivatives, Fair Value [Line Items]    
Assets Fair Value    997
Liabilities Fair Value 2,414   
Commodity Contract [Member] | Natural gas futures [Member] | Derivative Not Designated as Hedging Instruments [Member] | Other current assets [Member]
   
Derivatives, Fair Value [Line Items]    
Assets Fair Value 3   
Liabilities Fair Value