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Maintenance Contracts (Schedule Of Deferred Maintenance Revenue) (Details) (USD $)
3 Months Ended
Jul. 31, 2013
Jul. 31, 2012
Apr. 30, 2013
Maintenance Contracts [Abstract]      
Beginning balance $ 8,861,000 $ 8,302,000  
Revenue recognized during period (3,544,000) (3,683,000)  
New maintenance contracts 2,262,000 2,534,000  
Ending balance 7,579,000 7,153,000  
Long-term deferred maintenance revenue $ 700,000   $ 800,000