Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Product revenue	$ 0	$ 45	$ 0	$ 45
Royalty revenue	0	106	11	203
Contract revenue	2,014	1,188	4,191	1,659
Total revenue	2,014	1,339	4,202	1,907
Cost of product revenue	326	181	564	394
Cost of contract revenue	1,355	812	2,990	1,215
Total cost of revenue	1,681	993	3,554	1,609
Gross profit	333	346	648	298
Research and development expense	6,691	3,672	11,519	6,990
Sales, marketing, general and administrative expense	2,093	2,325	4,700	4,905
Total operating expenses	8,784	5,997	16,219	11,895
Loss from operations	(8,451)	(5,651)	(15,571)	(11,597)
Other (expense) income, net	(8)	(5)	(20)	(8)
Net loss	$ (8,459)	$ (5,656)	$ (15,591)	$ (11,605)
Net loss per share - basic and diluted	$ (0.10)	$ (0.08)	$ 0.19	$ (0.17)
Weighted-average shares outstanding - basic and diluted	81,321	69,373	79,973	68,747