Stock Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Stock Plans (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 202	$ 92	$ 783	$ 659
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	85	42	302	280
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 117	$ 50	$ 481	$ 379