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Activity of Stock Option by Exercise Price Range (Detail) (USD $)
12 Months Ended
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 $ 0.35 $ 0.35 $ 0.35
Range of Exercise Prices, upper range $ 6.74 $ 6.74 $ 7.08
Options Outstanding 5,422,130 4,641,039 4,716,439
Options Outstanding Weighted Average Remaining Life in Years 6 years 4 months 21 days 6 years 7 months 6 days 7 years 18 days
Options Outstanding Weighted Average Exercise Price $ 2.19 $ 2.23 $ 2.35
Options Exercisable 3,775,388 3,206,994 2,904,435
Weighted Average Exercise Price of Options Exercisable $ 2.37 $ 2.23 $ 2.20
Total intrinsic value of options exercised $ 215,541 $ 216,576 $ 1,049,489
Total fair value of options vested $ 1,170,738 $ 1,435,186 $ 1,648,292