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Unrecognized Tax Benefits (Details) (USD $)
In Thousands, unless otherwise specified
9 Months Ended
Jan. 31, 2013
Jan. 31, 2012
Apr. 30, 2012
Unrecognized Tax Benefits [Abstract]      
Gross unrecognized tax benefits $ 9,536   $ 7,538
Unrecognized tax benefits impacting effective tax rate if recognized 6,198    
Unrecognized tax benefits, accrued interest and penalties 390   249
Net interest and penalties included in income tax expense 141 99  
Best estimate for reasonably change in amount of gross unrecognized tax benefits is a decrease during 12 months $ 1,580    
Federal statute of limitations for income tax filings, years open 2010 and forward    
State statute of limitations for icome tax filings, years open 2008 and forward