Income Tax Contingencies (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
Oct. 31, 2011	Oct. 31, 2010	Apr. 30, 2011
Income Tax Contingency [Line Items]
Gross unrecognized tax benefits	$ 7,727		$ 6,148
Unrecognized tax benefits impacting effective tax rate if recognized	5,022
Unrecognized tax benefits, accrued interest and penalties	312		245
Interest and penalties included in income tax expense (benefit)	67	(95)
State examinations in progress	2
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Decrease in unrecognized tax benefits	$ 1,411

This element represents the total of accruals as of the date of the statement of financial position for interest recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity and the amount of statutory penalties for a tax position claimed or expected to be claimed by the entity, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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This element represents the total of interest expense recognized for an underpayment of income taxes computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity and the amount of statutory penalties in the period in which the entity claims or expects to claim a tax position, in its tax return, that does not meet the minimum statutory threshold to avoid payment of penalties.

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