Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Total stock-based compensation expense	$ 1,061	$ 1,131
Research and Development Expense [Member]
Total stock-based compensation expense	94	87
General and Administrative Expense [Member]
Total stock-based compensation expense	$ 967	$ 1,044