Annual report pursuant to Section 13 and 15(d)

Outstanding Stock Options, Vested and Expected to Vest, Non-Vested and Stock Options Currently Exercisable (Detail)

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Outstanding Stock Options, Vested and Expected to Vest, Non-Vested and Stock Options Currently Exercisable (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fully vested and expected to vest number of shares outstanding 5,821,461 7,274,630    
Fully vested and expected to vest Weighted average remaining contractual life 7 years 5 months 19 days 7 years 2 months 12 days    
Fully vested and expected to vest Weighted average price per share $ 13.93 $ 9.94    
Number of shares outstanding 5,858,613 7,292,031 9,131,494 7,928,729
Weighted average price per share $ 13.97 $ 9.95 $ 6.05 $ 4.33
Number of shares outstanding, exercisable 2,367,409 3,481,970    
Weighted average remaining contractual life, exercisable 6 years 2 months 1 day 5 years 9 months 26 days    
Weighted average price per share, exercisable $ 9.52 $ 5.71    
Non Vested Stock Options
       
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares outstanding 3,491,204 3,809,498    
Weighted average remaining contractual life 8 years 4 months 24 days 8 years 6 months 7 days    
Weighted average price per share $ 16.98 $ 13.82