Quarterly report pursuant to Section 13 or 15(d)

Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail)

v3.3.0.814
Stock Plans and Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense $ 562 $ 225 $ 1,852 $ 1,012
Research and development [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense 213 73 607 251
General and administrative [Member]        
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]        
Stock-based compensation expense $ 349 $ 152 $ 1,245 $ 761