Annual report pursuant to Section 13 and 15(d)

Stockholders' Equity - Stock Option Activity (Detail)

v3.8.0.1
Stockholders' Equity - Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Number of shares, Options exercised   (20,000)  
Weighted Average Exercise Price, Options exercised   $ 1.37  
Number of shares, Options vested and expected to vest 1,130,501 1,779,365  
Number of shares, Forfeited   (648,864)  
Number of shares, Options vested and expected to vest 1,085,501 1,130,501 1,779,365
Number of shares, Exercisable as of December 31, 2016   1,110,501  
Weighted average exercise price, Forfeited   $ 0.51  
Weighted average exercise price, Options vested and expected to vest $ 3.75 3.73 $ 4.37
Weighted average exercise price, Exercisable as of December 31, 2016   $ 3.78  
Total Weighted average intrinsic value, Options vested and expected to vest $ 1,351,080 $ 602,451 $ 666,396
Total Weighted Average Intrinsic Value, Options exercised 52,400    
Total weighted average intrinsic value, Exercisable $ 1,351,080    
Weighted average remaining contractual life (years), Options vested and expected to vest 3 years 11 months 5 days 4 years 11 months 5 days 6 years 3 months 25 days
Weighted average remaining contractual life (years), Exercisable as of December 31, 2016   3 years 11 months 12 days