Annual report pursuant to Section 13 and 15(d)

Share-Based Compensation - Summary of Employee Stock Option Activity (Detail)

v2.4.0.8
Share-Based Compensation - Summary of Employee Stock Option Activity (Detail) (Employee Stock Options [Member], USD $)
 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Employee Stock Options [Member]
    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares, Outstanding, Beginning balance 4,985,480 4,068,024
Number of shares, Granted 2,304,000 960,000
Number of shares, Exercised (55,379) (19,535)
Number of shares, Forfeited (2,011,671) (23,009)
Number of shares, Outstanding, Ending Balance 5,222,430 4,985,480
Number of shares, Vested or expected to vest 5,222,430  
Number of shares, Exercisable 4,063,646 3,752,296
Weighted average exercise price, Outstanding $ 0.42 $ 0.31
Weighted average exercise price, Granted $ 1.22 $ 0.91
Weighted average exercise price, Exercised $ 0.04 $ 0.04
Weighted average exercise price, Forfeited $ 1.22 $ 2.04
Weighted average exercise price, Outstanding $ 0.47 $ 0.42
Weighted average exercise price, Outstanding, Vested or expected to vest $ 0.47  
Weighted Average Exercise Price, Outstanding, Exercisable $ 0.30 $ 0.29
Weighted-average remaining life (years), Outstanding 4 years 8 months 5 days  
Weighted-average remaining life (years), Vested or expected to vest 4 years 8 months 5 days  
Weighted-average remaining life (years), Exercisable 3 years 8 months 19 days 4 years 3 months 11 days
Aggregate intrinsic value, Exercised $ 10,663 $ 8,726
Aggregate intrinsic value, Outstanding 432,392  
Aggregate intrinsic value, Vested or expected to vest 432,392  
Aggregate intrinsic value, Exercisable $ 432,392 $ 423,487