Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Total revenue	$ 11,518	$ 9,008	$ 37,136	$ 25,813
Cost of sales	6,109	3,753	17,235	10,549
Gross profit	5,409	5,255	19,901	15,264
Operating expenses:
Research and development	6,453	6,420	19,706	19,236
General and administrative	2,913	3,031	9,461	8,669
Sales and marketing	1,582	1,112	4,661	3,331
Total operating expenses	10,948	10,563	33,828	31,236
Loss from operations	(5,539)	(5,308)	(13,927)	(15,972)
Interest expense	(229)	(178)	(662)	(584)
Other income, net	139	40	315	83
Loss on extinguishment of debt				(246)
Net loss and comprehensive loss	$ (5,629)	$ (5,446)	$ (14,274)	$ (16,719)
Net loss per common share, basic and diluted	$ (0.33)	$ (0.43)	$ (0.88)	$ (1.35)
Weighted-average shares used to compute net loss per common share, basic and diluted	16,944,660	12,559,812	16,130,882	12,425,390
Product sales
Total revenue	$ 10,469	$ 8,323	$ 29,283	$ 22,171
Licensing, royalty and other revenue
Total revenue	$ 1,049	$ 685	$ 7,853	$ 3,642