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Stock-Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options issued to purchase common stock 5,584,420   4,796,005
Total unrecognized stock-based compensation expense related to stock options granted $ 700,000    
Total unrecognized stock-based compensation expense related to restricted stock awards granted $ 0    
Awards With Market Conditions      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock options issued to purchase common stock 321,000    
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant date fair value of stock options granted $ 0.71 $ 0.62  
Share based payment award forfeiture rates 76.00% 70.00%  
Total unrecognized stock-based compensation expense, weighted-average period Recognition 3 years    
Intrinsic value of options exercised $ 0 $ 13,000