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Stock Based Compensation - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Ratio of share reserve related to RSUs granted     2  
Minimum
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock units, vesting period     3 years  
Maximum
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock units, vesting period     5 years  
Non-vested option awards and RSU
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Unrecognized compensation expenses 32.8   32.8  
Weighted average period for recognition of compensation expense     1 year 9 months 22 days