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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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- Definition

Period over which consideration for sale of disposal group assets to be received.

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- Definition

Amount of gain (loss), after tax expense or benefit and not previously recognized, resulting from the sale of a business component.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 20

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759



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- Definition

The amount or range of possible amounts of gain that could be realized upon the resolution of a contingency.

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

-Publisher FASB

-Name Accounting Standards Codification

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- Definition

The value of all consideration given or received by the Entity in the significant acquisition or disposal.

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