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Income Taxes - Schedule of Difference in Provision (Benefit) for Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Federal statutory rate	35.00%	35.00%	35.00%
Tax at statutory rate	$ (8,929)	$ (18,378)	$ (26,638)
State income taxes, net of federal benefit	(1,271)	(1,076)	(3,050)
Tax over book basis in GreenFiber on sale	(2,570)
Non-deductible impairment of investment in GreenFiber			3,738
Non-deductible GreenFiber goodwill impairment and equity income in subsidiaries	1,548	180	1,182
Tax credits	(598)	(660)	(650)
Non-deductible expenses	505	494	823
Non-deductible stock option charges			73
Other, net	(491)	(512)	(1,132)
Income before provision (benefit) for income tax, net	1,799	(2,526)	1,593
Business Acquisition [Member]
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Increase (decrease) in valuation allowance	5,084	(5,084)
Other Valuation Allowance [Member]
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 13,605	$ 22,510	$ 27,247

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to increase (decrease) in the valuation allowance for deferred tax assets.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to the disposition of a business not qualifying as a discontinued operation.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to nondeductible impairment loss.

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Amount of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to tax credits. Including, but not limited to, research credit, foreign tax credit, investment tax credit, and other tax credits.

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