Fair Value Measurements and Derivative Instruments - Additional Information (Detail) (USD $)	12 Months Ended
Aug. 31, 2012	Aug. 31, 2011
Fair Value, Option, Quantitative Disclosures [Line Items]
Outstanding interest rate swaps at period end	$ 0
Gains (losses) remaining in other comprehensive income (loss)	0
Pretax losses continued to be deferred in accumulated other comprehensive income		500,000
Iowa Department Of Economic Development loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Non-interest bearing loans	2,000,000
Carrying value of debt	1,433,000	1,633,000
Fair value of debt	1,200,000
Commodity Contract [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Deferred loss, net of tax, recorded in other comprehensive income	$ 1,600,000
Commodity Contract [Member] \| Designated as Hedging Instrument [Member] \| Corn Futures [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Purchased corn positions	3,050,000
Commodity Contract [Member] \| Firm Priced Starch and Ethanol Futures [Member] \| Designated as Hedging Instrument [Member] \| Corn Futures [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Purchased corn positions	3,700,000
Commodity Contract [Member] \| Open Position [Member] \| Designated as Hedging Instrument [Member] \| Corn Futures [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Purchased corn positions	2,800,000

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

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No definition available.

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- Definition

Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date before deducting unamortized discount or premiums (if any). May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

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-Article 9

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-Name Accounting Standards Codification

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The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

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- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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-SubTopic 10

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- Definition

Fair value as of the balance sheet date of all interest rate derivative assets designated as cash flow hedging instruments.

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-Topic 815

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- Definition

The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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Amount of unrealized gain (loss) related to the increase or decrease in fair value of interest rate derivatives designated as cash flow hedging instruments, which was recorded in accumulated other comprehensive income to the extent that the cash flow hedge was determined to be effective.

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