Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation expense associated with research and development expense	$ 1,655	$ 1,184
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,419	$ 1,047