Stock Plans (Details 3) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 1,687	$ 1,039	$ 1,026
Increase in basic net income (loss) per share (in dollars per share)	$ (0.08)	$ (0.05)	$ (0.05)
Increase in diluted net income (loss) per share (in dollars per share)	$ (0.08)	$ (0.05)	$ (0.05)
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 519	$ 386	$ 341
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expenses	$ 1,168	$ 653	$ 685