Quarterly report pursuant to Section 13 or 15(d)

Employee Stock Plans (Narrative) (Details)

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Employee Stock Plans (Narrative) (Details) (USD $)
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]        
Additional common stock for stock-based compensation awards     2,360,000  
Shares repurchased during the period       724,064
Common stock repurchased, value       $ 10,600,000
Stock issued for stock options exercised 22,523 378,705 138,709 471,782
Warrants exercised, cash       2,983,000
Stock-based compensation expense 3,316,000 3,969,000 9,913,000 11,775,000
Stock Options And SARs [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total unrecognized compensation cost related to non-vested awards of restricted stock 2,100,000   2,100,000  
Expected cost recognized over weighted-average period     1.2  
Stock issued for stock options exercised     144,000  
Stock-based compensation expense 264,000 400,000 709,000 847,000
Restricted Stock [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total unrecognized compensation cost related to non-vested awards of restricted stock 20,600,000   20,600,000  
Expected cost recognized over weighted-average period     2.0  
Shares repurchased during the period 1,151 1,378 184,101 192,369
Common stock repurchased, value 100,000 100,000 4,200,000 2,800,000
Vesting period (years) market based     three  
Vesting period minimum (years) time based     three  
Vesting period maximum (years) time based     four  
Stock-based compensation expense 3,198,000 3,481,000 9,119,000 10,633,000
ESPP [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Authorized payroll deductions 15.00%   15.00%  
Authorized payroll deductions, value     25,000  
Fair market price of common stock     85.00%  
Maximum number of shares of common stock reserved for ESPP issuance 3,000,000   3,000,000  
Employees stock purchased   45,488 76,909 153,913
Employees stock purchased, per share value   $ 19.64 $ 18.69 $ 14.13
Original shares reserved for issuance 1,500,000   1,500,000  
Amended shares reserved for issuance 3,000,000   3,000,000  
Shares available for future issuance 1,600,000   1,600,000  
Stock-based compensation expense $ (146,000) $ 88,000 $ 85,000 $ 295,000
Warrant [Member]
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Warrant date issued     Jun. 30, 2002  
Warrants issued 274,207   274,207  
Common stock at an exercise price $ 11.94   $ 11.94  
Shares of common stock issued in exchange for warrants   274,207   274,207