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Note K - Stock Based Compensation Plan (Details) - Stock Option Activity (USD $)
 12 Months Ended 12 Months Ended
Apr. 30, 2013
Apr. 30, 2012
Apr. 30, 2011
Apr. 30, 2013
Minimum [Member]
Apr. 30, 2012
Minimum [Member]
Apr. 30, 2010
Minimum [Member]
Apr. 30, 2013
Maximum [Member]
Apr. 30, 2012
Maximum [Member]
Apr. 30, 2011
Maximum [Member]
Note K - Stock Based Compensation Plan (Details) - Stock Option Activity [Line Items]                  
Number of Shares (in Shares) 1,118,250 1,133,147 1,110,397            
Exercise Price per Share Lower Range Limit (in Dollars)       $ 11.83 $ 6.59 $ 6.59      
Exercise Price per Share Upper Range Limit (in Dollars)             45.72 24.47 24.47
Proceeds on Exercise $ 22,881,000 $ 21,897,000 $ 21,366,000            
Weighted Average Exercise Price per Share $ 20.46 $ 19.32 $ 19.24            
Number of Shares (in Shares) 40,000 73,750 23,750            
Exercise Price per Share Lower Range Limit (in Dollars)       44.14 24.69        
Exercise Price per Share Upper Range Limit (in Dollars)             45.46 45.72 22.87
Proceeds on Exercise $ 1,801,000 $ 2,355,000 $ 543,000            
Weighted Average Exercise Price per Share $ 45.02 $ 31.93 $ 22.87            
Number of Shares (in Shares) (35,750) (88,647)              
Exercise Price per Share Lower Range Limit (in Dollars)       11.83 6.59        
Exercise Price per Share Upper Range Limit (in Dollars)             23.34 24.69  
Proceeds on Exercise $ (790,000) $ (1,371,000)              
Weighted Average Exercise Price per Share $ 22.13 $ 15.46              
Expired (in Shares)     (1,000)            
Expired                 $ 11.62
Expired (in Dollars)     (12,000)            
Expired     $ 11.62            
Number of Shares (in Shares) 1,122,500 1,118,250 1,133,147            
Exercise Price per Share Lower Range Limit (in Dollars)       11.90 11.83 6.59      
Exercise Price per Share Upper Range Limit (in Dollars)             $ 45.72 $ 45.72 $ 24.47
Proceeds on Exercise $ 23,892,000 $ 22,881,000 $ 21,897,000            
Weighted Average Exercise Price per Share $ 21.28 $ 20.46 $ 19.32