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Subsidiary Guarantors (Schedule Of Condensed Consolidating Balance Sheet) (Parenthetical) (Detail) (USD $)
Jul. 31, 2012
Apr. 30, 2012
Jul. 31, 2011
Class A Common Stock [Member]
     
Condensed Financial Statements, Captions [Line Items]      
Common Stock, Authorized shares 100,000,000 100,000,000  
Common stock, par value $ 0.01 $ 0.01  
Common stock, issued shares 26,367,000 25,991,000  
Common Stock, outstanding shares 26,367,000 25,991,000 25,898,000
Class B Common Stock [Member]
     
Condensed Financial Statements, Captions [Line Items]      
Common Stock, Authorized shares 1,000,000 1,000,000  
Common stock, par value $ 0.01 $ 0.01  
Common stock, votes (in votes per share) $ 10 $ 10  
Common stock, issued shares 988,000 988,000  
Common Stock, outstanding shares 988,000 988,000 988,000