Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation expense associated with research and development expense	$ 1,903	$ 1,395	$ 3,671	$ 3,050
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,863	$ 1,503	$ 3,506	$ 2,922