Stock-based Compensation - Details of Stock-based Compensation Expense Recorded (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 | $ 314 | $ 756 |
Research and Development [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Total stock-based compensation | 89 | 243 |
General and Administrative [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||
Total stock-based compensation | $ 225 | $ 513 |