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Divestiture Transactions and Discontinued Operations - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended |  | 3 Months Ended |
--- | --- | --- | --- | ---
Jul. 31, 2013 | Jul. 31, 2013 BioFuels Assets [Member] | Jul. 31, 2012 Maine Energy Facility [Member] | Oct. 31, 2014 Maine Energy Facility [Member] Scenario, Forecast [Member] Maximum [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |
Undiscounted purchase consideration |  | $ 2,000 | $ 6,650 |
Undiscounted purchase consideration paid in installments | 5 years |  | 21 years |
Loss on disposal of discontinued operations, net of tax | (378) |  |  |
Potential gain on divestiture |  |  |  | $ 1,600

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