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Income Taxes (Narrative) (Details) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Income Taxes [Line Items]      
Operating loss carryforwards for state income tax purposes $ 93,805    
Gross unrecognized tax benefits 8,938 7,538 6,148
Unrecognized tax benefits impacting effective tax rate if recognized 5,810    
Net increase of unrecognized tax benefits 1,400    
Unrecognized tax benefits, accrued interest and penalties 286 249  
Increase (decrease) in tax expense due to net interest and penalties 37 4  
Best estimate for reasonably change in amount of gross unrecognized tax benefits is a decrease during 12 months 1,491    
Valuation allowance for deferred tax assets 0 0  
Change in valuatin allowance $ 0 $ 0  
Minimum [Member]
      
Income Taxes [Line Items]      
Operating loss carryforwards expiration date 2016    
Maximum [Member]
      
Income Taxes [Line Items]      
Operating loss carryforwards expiration date 2033