Stock Plans (Details) - USD ($) $ in Thousands |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2017 |
Jun. 30, 2016 |
Jun. 30, 2017 |
Jun. 30, 2016 |
|
| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation expenses | $ 382 | $ 249 | $ 803 | $ 581 |
| Research and development [Member] | ||||
| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation expenses | 128 | 85 | 245 | 217 |
| General and administrative [Member] | ||||
| Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items] | ||||
| Total stock-based compensation expenses | $ 254 | $ 164 | $ 558 | $ 364 |