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Stock Incentive Plans And Stock Purchase Plans (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended 6 Months Ended 1 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
May 10, 2012
May 10, 2012
Extended Maturity [Member]
Jun. 30, 2012
1996 Non-Qualified Employee Stock Purchase Plan [Member]
Jun. 30, 2012
Stock Options [Member]
Year
Jun. 30, 2012
Restricted Stock [Member]
Jun. 30, 2012
Deferred Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                    
Vesting period expiration year           10        
Shares available for future grants and awards under Stock Incentive Plans 4,200,000   4,200,000   5,029,717          
Vesting period of options, maximum years               10    
Number of years over which options become exercisable on a pro rata basis               3    
Vesting period of options, years                 3 years 5 years
Restricted stock granted to employees     446,451              
Restricted stock granted to non-employee directors     14,625              
Percentage of market value of common stock at which employees are permitted to purchase             85.00%      
Shares issued             66,311      
Shares reserved for issuance             489,000      
Stock-based compensation expense related to its Stock Incentive Plans and Non-Qualified Plan $ 6.1 $ 13.1 $ 6.7 $ 13.2            
Net excess tax benefit recognized in additional paid-in capital related to the exercise of stock options and the vesting of restricted stock     $ 3.3