Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation expense associated with research and development expense	$ 1,345	$ 1,051	$ 3,698	$ 3,013
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,235	$ 879	$ 3,516	$ 2,709