Quarterly report pursuant to Section 13 or 15(d)

Employee Stock Plans (Stock Options And SARs Transactions) (Details)

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Employee Stock Plans (Stock Options And SARs Transactions) (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
Jan. 31, 2012
Jan. 31, 2011
Jan. 31, 2012
Jan. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Options, Exercised (22,523) (378,705) (138,709) (471,782)
Stock Options And SARs [Member]
        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Options, Outstanding, April 30, 2011     1,833,000  
Options, Granted     48,000  
Options, Exercised     (144,000)  
Options, Forfeited/expired     (134,000)  
Options, Outstanding, January 31, 2012 1,603,000   1,603,000  
Options Exercisable, January 31, 2012 1,132,000   1,132,000  
Weighted-Average Exercise Price, Outstanding, April 30, 2011     13.78  
Weighted-Average Exercise Price, Granted 22.71   22.71  
Weighted-Average Exercise Price, Exercised 14.00   14.00  
Weighted-Average Exercise Price, Forfeited/expired 16.22   16.22  
Weighted-Average Exercise Price, Outstanding, January 31, 2012 13.80   13.80  
Weighted-Average Exercise Price, Exercisable, Outstanding, January 31, 2012 14.07   14.07  
Weighted-Average Remaining Contractual Life (In Years), Outstanding, January 31, 2012 3.38   3.38  
Weighted-Average Remaining Contractual Life (In Years), Exercisable, January 31, 2012     2.71  
Aggregate Intrinsic Value, Outstanding, January 31, 2012 5,867   5,867  
Aggregate Intrinsic Value, Exercisable, January 31, 2012 4,027   4,027