Condensed Consolidated Statements of Operations (unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Government grant revenue	$ 0	$ 155	$ 0	$ 220
Product revenue	329	92	1,167	146
Total revenue	329	247	1,167	366
Cost of product revenue	399	56	1,287	96
Gross profit (loss)	(70)	191	(120)	270
Expenses
Research and development	1,131	1,193	4,231	3,252
Sales and marketing	342	467	1,457	1,239
General and administrative	1,398	1,714	4,846	4,432
Total expenses	2,871	3,374	10,534	8,923
Operating loss	(2,941)	(3,183)	(10,654)	(8,653)
Interest and other income (expense)
Interest expense, net	0	0	0	(1)
Change in fair value of warrants liabilities (expense)	200	73	1,323	(1,177)
Cease-use expense	0	0	(94)	0
Other expense	(9)	(183)	(27)	(183)
Inducement charge for Series C warrants	0	0	0	(3,050)
Interest and other income (expense), net	191	(110)	1,202	(4,411)
Net loss	(2,750)	(3,293)	(9,452)	(13,064)
Loss on extinguishment of convertible preferred stock	(3,651)	0	(3,651)	0
Net loss attributable to common stockholders	$ (6,401)	$ (3,293)	$ (13,103)	$ (13,064)
Net loss per share attributable to common stockholders, basic and diluted (in usd per share)	$ (0.41)	$ (0.33)	$ (0.85)	$ (1.60)
Weighted-average common shares outstanding used to calculate basic and diluted net loss per common share (in shares)	15,761,530	10,040,079	15,363,648	8,178,897