Summary of Stock-Based Compensation Recognized (Detail) - USD ($) $ in Thousands |
12 Months Ended | |
---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Total stock-based compensation | $ 863 | $ 635 |
Research and development | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Total stock-based compensation | 699 | 185 |
General and Administrative | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Total stock-based compensation | $ 164 | $ 450 |