Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 625	$ 479	$ 576
Costs and expenses:
Cost of goods sold	517	690	746
Research and development	8,453	5,799	3,330
Selling, general and administrative	5,757	6,395	4,108
Total costs and expenses	14,727	12,884	8,184
Operating loss	(14,102)	(12,405)	(7,608)
Other income (expense):
Interest income	118	95
Interest expense			(1,736)
Change in fair value of convertible preferred stock warrant liability			250
Change in fair value of maturity date preferred stock warrant liability			10
Change in fair value of convertible shareholder notes derivative liability			(1,224)
Other expense	(3)	2	(2)
Other income (expense), net	115	97	(2,702)
Net loss	$ (13,987)	$ (12,308)	$ (10,310)
Net loss per share, basic and diluted (in dollars per share)	$ (0.36)	$ (0.32)	$ (1.23)
Weighted-average shares used in computing net loss per share, basic and diluted (in shares)	38,377,606	38,160,543	8,368,284
Product [Member]
Revenue:
Total revenue	$ 282	$ 389	$ 517
Collaboration Agreement [Member]
Revenue:
Total revenue	$ 343	$ 90	$ 59