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Summary of Significant Accounting Policies - Investments in Unconsolidated Entities - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended | 1 Months Ended | 12 Months Ended | 0 Months Ended | 12 Months Ended
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Apr. 30, 2014 | Apr. 30, 2013 | Apr. 30, 2012 | Dec. 05, 2013 GreenFiber [Member] | Apr. 30, 2014 GreenFiber [Member] | Dec. 31, 2013 Tompkins County Recycling LLC [Member] | Apr. 30, 2014 Tompkins County Recycling LLC [Member]
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Sale of equity method investment |  |  |  | $ 18,000 |  |  |
Gross cash proceeds |  |  |  | 19,194 |  |  |
Adjustment of working capital |  |  |  | 1,194 |  |  |
Percentage of net cash proceeds |  |  |  | 50.00% |  |  |
Net cash proceeds | 3,442 |  |  |  | 3,442 |  |
Unrealized losses relating to derivative instruments |  |  |  |  | 593 |  |
Gain on sale of equity method investment | 593 |  |  |  | 593 |  |
Equity method investment membership interest |  |  |  |  | 50.00% | 50.00% |
Equity contribution |  |  |  |  |  | 425 |
Price to purchase acquired assets prior to the acquisition date |  |  |  |  |  |  | 300
Gain through loss from equity method investments | $ (936) | $ (4,441) | $ (9,994) |  |  |  | $ 106

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- Definition Fair value at acquisition-date of the equity interest in the acquiree held by the acquirer, immediately before the acquisition date for businesses combined in stages. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463 + Details
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