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Fair Value Measurements and Derivative Instruments - Additional Information (Detail) (USD $)
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12 Months Ended |
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Aug. 31, 2012
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Aug. 31, 2011
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Outstanding interest rate swaps at period end |
$ 0 |
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| Gains (losses) remaining in other comprehensive income (loss) |
0 |
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| Pretax losses continued to be deferred in accumulated other comprehensive income |
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500,000 |
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Iowa Department of Economic Development Loans [Member]
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Non-interest bearing loans |
2,000,000 |
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| Carrying value of debt |
1,433,000 |
1,633,000 |
| Fair value of debt |
1,200,000 |
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Commodity Contract [Member]
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Deferred loss, net of tax, recorded in other comprehensive income |
$ 1,600,000 |
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Commodity Contract [Member] | Designated as Hedging Instrument [Member] | Corn Futures [Member]
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Purchased corn positions |
6,500,000 |
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Commodity Contract [Member] | Firm Priced Starch and Ethanol Futures [Member] | Designated as Hedging Instrument [Member] | Corn Futures [Member]
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Purchased corn positions |
3,700,000 |
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Commodity Contract [Member] | Open Position [Member] | Designated as Hedging Instrument [Member] | Corn Futures [Member]
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| Fair Value, Option, Quantitative Disclosures [Line Items] |
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| Purchased corn positions |
2,800,000 |
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