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Summary of Significant Accounting Policies - Summarized Balance Sheet Financial Information of Investments in Unconsolidated Affiliates (Detail) (GreenFiber [Member], USD $)
In Thousands, unless otherwise specified
Apr. 30, 2013
Apr. 30, 2012
GreenFiber [Member]
   
Schedule of Equity Method Investments [Line Items]    
Current assets $ 16,644 $ 17,513
Noncurrent assets 28,139 34,597
Current liabilities 19,247 12,815
Noncurrent liabilities $ 1,227 $ 5,382