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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
	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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Equity method investment sales price consideration.

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Equity method investment final consideration.

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Equity method investment working capital portion of the final consideration.

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Percentage of net cash proceeds.

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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.

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-Name Accounting Standards Codification

-Topic 805

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-Section 50

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of gain (loss) on sale or disposal of an equity method investment.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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