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Summary of Information Regarding Option Activity (Detail) (USD $)
 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Options Outstanding    
Options outstanding at January 1, 2012 2,823,400 2,719,100
Granted 357,190  
Exercised (426,100)  
Forfeited/Cancelled (128,800)  
Options outstanding at September 30, 2012 2,625,690 2,719,100
Options exercisable at September 30, 2012 1,549,700  
Vested and expected to vest at September 30, 2012 2,479,847 [1]  
Weighted average exercise price per share    
Options outstanding at January 1, 2012 $ 4.05 $ 4.09
Granted $ 3.57  
Exercised $ 3.12  
Forfeited/Cancelled $ 4.72  
Options outstanding at September 30, 2012 $ 4.11 $ 4.09
Options exercisable at September 30, 2012 $ 4.32  
Vested and expected to vest at September 30, 2012 $ 4.11 [1]  
Weighted average remaining contractual term (in years)    
Options outstanding at September 30, 2012 6 years 2 months 16 days  
Options exercisable at September 30, 2012 4 years 8 months 9 days  
Vested and expected to vest at September 30, 2012 6 years 1 month 2 days [1]  
Aggregate intrinsic value    
Options outstanding at September 30, 2012 $ 4,960,713  
Options exercisable at September 30, 2012 2,632,460  
Vested and expected to vest at September 30, 2012 $ 4,678,761 [1]  
[1] This represents the number of vested options as of September 30, 2012 plus the number of unvested options expected to vest as of September 30, 2012 based on the unvested outstanding options at September 30, 2012 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.