Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Stock-based compensation expense associated with research and development expense	$ 893	$ 797	$ 2,865	$ 3,195
Stock-based compensation expense associated with general and administrative expense	$ 779	$ 697	$ 2,548	$ 2,389