CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Product revenue	$ 10,797	$ 10,175	$ 27,328	$ 27,058
Cost of product revenue	5,348	5,451	13,402	14,690
Gross profit on product revenue	5,449	4,724	13,926	12,368
Government contracts revenue	2,285	261	5,380	261
Operating expenses:
Research and development	7,886	7,033	25,927	22,507
Selling, general and administrative	12,180	12,161	39,907	36,314
Amortization of intangible assets	50	50	151	151
Total operating expenses	20,116	19,244	65,985	58,972
Loss from operations	(12,382)	(14,259)	(46,679)	(46,343)
Non-operating (expense) income, net:
Foreign exchange loss		(61)	(59)	(77)
Interest expense	(1,090)	(586)	(2,122)	(1,899)
Other income, net	104	114	3,722	293
Total non-operating (expense) income, net	(986)	(533)	1,541	(1,683)
Loss before income taxes	(13,368)	(14,792)	(45,138)	(48,026)
Provision (benefit) for income taxes	50	(416)	3,961	1,379
Net loss	$ (13,418)	$ (14,376)	$ (49,099)	$ (49,405)
Net loss per share:
Basic	$ (0.12)	$ (0.14)	$ (0.46)	$ (0.49)
Diluted	$ (0.12)	$ (0.14)	$ (0.46)	$ (0.49)
Weighted average shares outstanding used for calculating net loss per share:
Basic	109,846	102,769	106,159	101,273
Diluted	109,846	102,769	106,159	101,273