Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Stock-based compensation expense associated with research and development expense	$ 973	$ 868	$ 1,962	$ 1,972
Stock-based compensation expense associated with general and administrative expense	$ 984	$ 920	$ 1,830	$ 1,769