Income Taxes - Schedule of Difference in Provision (Benefit) for Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Federal statutory rate	35.00%	35.00%	35.00%
Tax benefit at statutory rate	$ (18,378)	$ (26,638)	$ (9,341)
State income taxes, net of federal benefit	(1,076)	(3,050)	281
Non-deductible impairment of investment in GreenFiber		3,738
Non-deductible GreenFiber goodwill impairment and equity income in subsidiaries	180	1,182
Tax credits	(660)	(650)	(637)
Non-deductible expenses	494	823	408
Non-deductible stock option charges		73	107
Other, net	(512)	(1,132)	(87)
Income before provision (benefit) for income tax, net	(2,526)	1,593	(23,723)
Business Acquisition [Member]
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Increase (decrease) in valuation allowance	(5,084)
Other Valuation Allowance [Member]
Income Loss From Operations Before Provision Benefit For Income Taxes [Line Items]
Increase (decrease) in valuation allowance	$ 22,510	$ 27,247	$ (14,454)

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to pretax Income or Loss from continuing operations; income tax expense or benefit may include interest and penalties on tax uncertainties based on the entity's accounting policy.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to changes in the valuation allowance for deferred tax assets in the period.

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The amount of income tax expense or benefit for the period computed by applying the domestic federal statutory tax rates to pretax income from continuing operations.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to nondeductible expenses under enacted tax laws, or differences in the methodologies used to determine expense amounts for financial statements prepared in accordance with generally accepted accounting principles, not otherwise listed in the existing taxonomy.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations attributable to differences in the deductibility of incentive stock options and other equity-based compensation costs in accordance with generally accepted accounting principles and enacted tax laws.

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The sum of other amounts reflected in the reconciliation of the statutory tax provision (benefit) to the actual tax provision (benefit).

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The portion of the difference, between total income tax expense or benefit as reported in the Income Statement for the period and the expected income tax expense or benefit computed by applying the domestic federal statutory income tax rates to pretax income from continuing operations, that is attributable to state and local income tax expense or benefit.

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