Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock-based compensation expense associated with research and development expense	$ 1,768	$ 1,655
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,643	$ 1,419