Stock Plans (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Total stock-based compensation expenses | $ 402 | $ 382 | $ 834 | $ 803 |
| Research and development [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Total stock-based compensation expenses | 156 | 128 | 318 | 245 |
| General and administrative [Member] | ||||
| Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items] | ||||
| Total stock-based compensation expenses | $ 246 | $ 254 | $ 516 | $ 558 |