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Unrecognized Tax Benefits (Details) (USD $)
In Thousands, unless otherwise specified
6 Months Ended
Oct. 31, 2012
Oct. 31, 2011
Apr. 30, 2012
Unrecognized Tax Benefits [Abstract]      
Gross unrecognized tax benefits $ 9,271   $ 7,538
Unrecognized tax benefits impacting effective tax rate if recognized 6,026    
Unrecognized tax benefits, accrued interest and penalties 357   249
Net interest and penalties included in income tax expense 108 29  
Best estimate for reasonably change in amount of gross unrecognized tax benefits is a decrease during 12 months $ 1,565    
Federal statute of limitations for income tax filings, years open 2009 and forward    
State statute of limitations for icome tax filings, years open 2008 and forward