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Stockholders' Equity - Activity of Stock Option by Exercise Price Range (Detail) (USD $)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]        
Range of Exercise Prices, lower range (in dollars per share) $ 0.35 $ 0.35 $ 0.35  
Range of Exercise Prices, upper range (in dollars per share) $ 6.55 $ 6.74 $ 6.74  
Options Outstanding (in shares) 5,279,229 5,422,130 4,641,039 4,716,439
Options Outstanding, Weighted Average Remaining Life in Years 5 years 10 months 17 days 6 years 4 months 21 days 6 years 7 months 6 days  
Options Outstanding, Weighted Average Exercise Price (in dollars per share) $ 2.11 $ 2.19 $ 2.23 $ 2.35
Options Exercisable (in shares) 4,012,378 3,775,388 3,206,994 2,904,435
Weighted Average Exercise Price of Options Exercisable (in dollars per share) $ 2.28 $ 2.37 $ 2.23 $ 2.2
Total intrinsic value of options exercised $ 111,595 $ 215,541 $ 216,576  
Total fair value of options vested $ 1,248,067 $ 1,170,738 $ 1,435,186