Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock-based compensation expense associated with research and development expense	$ 1,051	$ 893	$ 3,013	$ 2,865
Stock-based compensation expense associated with general and administrative expense	$ 879	$ 779	$ 2,709	$ 2,548