Stock Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Stock Plans (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 249	$ 76	$ 581	$ 567
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	85	35	217	238
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 164	$ 41	$ 364	$ 329