Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Total stock-based compensation expense	$ 946	$ 933	$ 2,818	$ 2,406
Research and Development [Member]
Total stock-based compensation expense	85
General and Administrative Expense [Member]
Total stock-based compensation expense	$ 861		2,549	2,097
Research and Development Expense [Member]
Total stock-based compensation expense		135	$ 269	$ 309
General and Administrative [Member]
Total stock-based compensation expense		$ 798