Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock-based compensation expense associated with research and development expense	$ 1,472	$ 1,345	$ 4,522	$ 3,698
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,405	$ 1,235	$ 4,327	$ 3,516