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Maintenance Contracts (Schedule Of Deferred Maintenance Revenue) (Details) (USD $)
12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Maintenance Contracts [Abstract]    
Deferred maintenance revenue beginning balance $ 8,302,000 $ 8,420,000
Deferred maintenance revenue recognized during period (15,622,000) (16,090,000)
Deferred maintenance revenue of new maintenance contracts 16,181,000 15,972,000
Deferred maintenance revenue ending balance 8,861,000 8,302,000
Long-term deferred maintenance revenue $ 800,000 $ 300,000