Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Total stock-based compensation expense	$ 811	$ 342	$ 1,872	$ 1,473
Research and Development [Member]
Total stock-based compensation expense	90
General and Administrative Expense [Member]
Total stock-based compensation expense	$ 721		1,688	1,299
Research and Development Expense [Member]
Total stock-based compensation expense		87	$ 184	$ 174
General and Administrative [Member]
Total stock-based compensation expense		$ 255