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Stock Incentive Plans And Stock Purchase Plans (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Class of Stock [Line Items]    
Shares available for future grants and awards under Stock Incentive Plans 1,300,000  
Stock-based compensation expense related to its Stock Incentive Plans and Non-Qualified Plan $ 7.0 $ 6.5
Net excess tax benefit recognized in additional paid-in capital related to the exercise of stock options and the vesting of restricted stock $ 2.1  
1996 Non-Qualified Employee Stock Purchase Plan [Member]
    
Class of Stock [Line Items]    
Percentage of market value of common stock at which employees are permitted to purchase 85.00%  
Shares issued 27,418  
Shares reserved for issuance 528,000  
Stock Options [Member]
    
Class of Stock [Line Items]    
Vesting period of options, maximum years 10  
Number of years over which options become exercisable on a pro rata basis 3  
Restricted Stock [Member]
    
Class of Stock [Line Items]    
Vesting period of options, years three  
Deferred Stock Awards [Member]
    
Class of Stock [Line Items]    
Vesting period of options, years five