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Stock Based Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Option awards granted     0  
Long-term equity incentive plan, termination date     2014-10-19  
Number of shares authorized under plan 8,550,000   8,550,000  
Options and restricted stock granted, net of forfeitures     8,045,383  
Total intrinsic value of options exercised $ 0.3 $ 1.2 $ 4.4 $ 2.6
Restricted Stock
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting period of equity awards granted to employees, years     4 years  
Unrecognized compensation cost related to stock option awards granted under the equity incentive plan $ 26.7   $ 26.7  
Expected weighted-average period to recognize the cost of stock awards (in years)     2 years 10 months 24 days