Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Total revenue	$ 9,178	$ 11,518	$ 27,850	$ 37,136
Cost of sales	4,824	6,109	14,692	17,235
Gross profit	4,354	5,409	13,158	19,901
Operating expenses:
Research and development	3,395	6,453	10,912	19,706
General and administrative	3,050	2,913	9,501	9,461
Sales and marketing	1,491	1,582	4,094	4,661
Total operating expenses	7,936	10,948	24,507	33,828
Loss from operations	(3,582)	(5,539)	(11,349)	(13,927)
Interest expense	(170)	(229)	(567)	(662)
Other income, net	89	139	327	315
Net loss and comprehensive loss	$ (3,663)	$ (5,629)	$ (11,589)	$ (14,274)
Net loss per common share, basic and diluted	$ (0.21)	$ (0.33)	$ (0.67)	$ (0.88)
Weighted-average shares used to compute net loss per common share, basic and diluted	17,312,226	16,944,660	17,183,306	16,130,882
Product sales
Total revenue	$ 8,370	$ 10,469	$ 25,396	$ 29,283
Product sales
Total revenue	8,370	10,469	25,396	29,283
Licensing, royalty and other revenue
Total revenue	$ 808	$ 1,049	$ 2,454	$ 7,853