Stock Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
Stock Plans (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 76	$ 60	$ 567	$ 386
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	35	28	238	173
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 41	$ 32	$ 329	$ 213