Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Stock-based compensation expense associated with research and development expense	$ 1,698	$ 1,472	$ 5,369	$ 4,522
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,864	$ 1,405	$ 5,370	$ 4,327