Stockholders' Equity (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Benefits and Share-based Compensation	$ 3,117	$ 3,867	$ 3,252
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Benefits and Share-based Compensation	1,180	2,557	2,987
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Benefits and Share-based Compensation	$ 1,937	$ 1,310	$ 265