Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-based compensation expense associated with research and development expense	$ 1,395	$ 1,169	$ 3,050	$ 2,353
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,503	$ 1,234	$ 2,922	$ 2,281