Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue:
Total revenue	$ 1,804	$ 3,931	$ 3,589	$ 6,242
Costs and expenses:
Research and development	4,048	3,749	7,949	8,467
Selling, general and administrative	6,722	7,611	13,776	13,366
Total costs and expenses	15,590	14,818	30,933	28,564
Loss from operations	(13,786)	(10,887)	(27,344)	(22,322)
Interest expense, net	(2,000)	(1,506)	(3,782)	(3,074)
Other income, net	139	69	332	159
Net loss and comprehensive loss	$ (15,647)	$ (12,324)	$ (30,794)	$ (25,237)
Net loss per share — basic and diluted	$ (0.35)	$ (0.32)	$ (0.69)	$ (0.68)
Weighted-average number of common shares used in computing net loss per share — basic and diluted	44,426,402	38,263,486	44,354,771	37,127,208
Product [Member]
Revenue:
Total revenue	$ 1,274	$ 1,220	$ 2,588	$ 2,268
Costs and expenses:
Cost of product revenue	4,820	3,458	9,208	6,731
Research [Member]
Revenue:
Total revenue	71	$ 2,711	213	$ 3,974
Contribution [Member]
Revenue:
Total revenue	$ 459		$ 788