Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue:
Total revenue	$ 1,785	$ 2,311
Costs and expenses:
Research and development	3,901	4,718
Selling, general and administrative	7,055	5,755
Total costs and expenses	15,344	13,746
Loss from operations	(13,559)	(11,435)
Interest expense, net	(1,782)	(1,568)
Other income, net	194	90
Net loss and comprehensive loss	$ (15,147)	$ (12,913)
Net loss per share — basic and diluted	$ (0.34)	$ (0.36)
Weighted-average number of common shares used in computing net loss per share — basic and diluted	44,282,345	35,978,306
Product [Member]
Revenue:
Total revenue	$ 1,314	$ 1,048
Costs and expenses:
Cost of product revenue	4,388	3,273
Research [Member]
Revenue:
Total revenue	142	$ 1,263
Contribution [Member]
Revenue:
Total revenue	$ 329