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Investments in Unconsolidated Entities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended			1 Months Ended					0 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Apr. 30, 2013	May 31, 2013 GreenFiber [Member]	Oct. 31, 2013 GreenFiber [Member]	Jun. 28, 2013 GreenFiber [Member]	Apr. 30, 2013 GreenFiber [Member]	Dec. 01, 2011 GreenFiber [Member]	Dec. 05, 2013 GreenFiber [Member] Subsequent Event [Member]	Oct. 31, 2013 Tompkins County Recycling LLC [Member]	Apr. 30, 2013 Tompkins County Recycling LLC [Member]
Investment Holdings [Line Items]
Percentage of equity-method ownership interest					50.00%					50.00%
Equity method investment	$ 2,731		$ 3,766		$ 2,439		$ 3,509			$ 291	$ 257
Loan and security agreement guaranty						750		2,200
Liability in other long-term liabilities							2,073
Payment to satisfy the guaranty and pay off the term loan in full	2,148	1,000		2,073
Total cash consideration									$ 18,000