Fair Value Measurements and Derivative Instruments - Effect of Derivative Instruments on Company's Financial Performance (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
May 31, 2014
May 31, 2013
May 31, 2014
May 31, 2013
Designated as Hedging Instrument [Member] | Cash flow hedges [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in OCI $ (3,368) $ (27) $ (9,607) $ 386
Amount of Gain (Loss) Reclassified from AOCI into Income (4,016) 241 (9,484) 4,016
Amount of Gain (Loss) Recognized in Income (458) (474) (1,926) (600)
Designated as Hedging Instrument [Member] | Cash flow hedges [Member] | Corn futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in OCI 760 530 81 (43)
Amount of Gain (Loss) Reclassified from AOCI into Income 1,744 596 (2,116) 4,087
Amount of Gain (Loss) Recognized in Income (198) (474) (1,595) (589)
Designated as Hedging Instrument [Member] | Cash flow hedges [Member] | Ethanol futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in OCI (4,128) (557) (9,688) 429
Amount of Gain (Loss) Reclassified from AOCI into Income (5,760) (355) (7,368) (71)
Amount of Gain (Loss) Recognized in Income (260)   (331) (11)
Designated as Hedging Instrument [Member] | Fair value hedges [Member] | Corn futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (21) 143 75 127
Derivative Not Designated as Hedging Instruments [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (849) 274 (559) (36)
Derivative Not Designated as Hedging Instruments [Member] | Ethanol futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income     64  
Derivative Not Designated as Hedging Instruments [Member] | Natural gas futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income (854) 294 (634) (16)
Derivative Not Designated as Hedging Instruments [Member] | Natural gas options [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income   (20)   (20)
Derivative Not Designated as Hedging Instruments [Member] | Soybean meal futures [Member]
       
Derivative Instruments, Gain (Loss) [Line Items]        
Amount of Gain (Loss) Recognized in Income $ 5   $ 11