Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Product revenue	$ 2,300	$ 12,849	$ 6,452
Royalty revenue	1,568	1,803	1,165
Contract revenue	7,023	109	1,571
Total revenue	10,891	14,761	9,188
Cost of product revenue	4,359	10,320	6,384
Cost of contract revenue	5,517	54	796
Total cost of revenue	9,876	10,374	7,180
Gross profit	1,015	4,387	2,008
Research and development expense	15,096	12,134	8,680
Sales, marketing, general and administrative expense	10,156	8,743	7,879
Gain on sale of previously reserved inventory	0	(32)	(1)
Total operating expenses	25,252	20,845	16,558
Loss from operations	(24,237)	(16,458)	(14,550)
Other income (expense), net	(6)	(14)	8
Net loss	$ (24,243)	$ (16,472)	$ (14,542)
Net loss per share - basic and diluted	$ (0.33)	$ (0.32)	$ (0.31)
Weighted-average shares outstanding - basic and diluted	72,786	51,958	46,540