Fair Value Measurements and Derivative Instruments - Fair Value of Company's Derivative by Contract Type (Detail) (USD $) In Thousands, unless otherwise specified	Nov. 30, 2012	Aug. 31, 2012
Derivatives, Fair Value [Line Items]
Assets Fair Value	$ 88	$ 12
Liabilities Fair Value	495	1,434
Corn Futures [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Assets Fair Value	88	12
Liabilities Fair Value		126
Corn Futures [Member] | Fair Value Hedging [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Assets Fair Value
Liabilities Fair Value	238	602
Ethanol Futures [Member] | Cash Flow Hedging [Member] | Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Assets Fair Value
Liabilities Fair Value	57	706
Natural Gas Futures [Member] | Not Designated as Hedging Instrument [Member] | Other Current Assets [Member] | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Assets Fair Value
Liabilities Fair Value	$ 200