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