Statements of Comprehensive Loss Parenthetical (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based compensation expense associated with research and development expense	$ 1,169	$ 973	$ 2,353	$ 1,962
Stock-based compensation expense associated with selling, general and administrative expense	$ 1,234	$ 984	$ 2,281	$ 1,830