CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Product revenue	$ 43,568,000	$ 37,183,000	$ 34,223,000
Cost of product revenue	22,531,000	20,295,000	23,464,000
Gross profit on product revenue	21,037,000	16,888,000	10,759,000
Government contract revenue	7,758,000	2,092,000
Operating expenses:
Research and development	33,710,000	31,322,000	25,643,000
Selling, general and administrative	52,413,000	48,753,000	45,989,000
Amortization of intangible assets	202,000	202,000	202,000
Impairment of long-lived assets	0	150,000	0
Total operating expenses	86,325,000	80,427,000	71,834,000
Loss from operations	(57,530,000)	(61,447,000)	(61,075,000)
Non-operating income (expense), net:
Gain from revaluation of warrant liability			3,566,000
Foreign exchange (loss) gain	(10,000)	21,000	(396,000)
Interest expense	(3,022,000)	(2,445,000)	(1,705,000)
Other income, net	3,864,000	1,140,000	71,000
Total non-operating income (expense) , net	832,000	(1,284,000)	1,536,000
Loss before income taxes	(56,698,000)	(62,731,000)	(59,539,000)
Provision (benefit) for income taxes	3,887,000	175,000	(3,671,000)
Net loss	$ (60,585,000)	$ (62,906,000)	$ (55,868,000)
Net loss per share:
Basic	$ (0.56)	$ (0.62)	$ (0.58)
Diluted	$ (0.56)	$ (0.62)	$ (0.61)
Weighted average shares outstanding used for calculating net loss per share:
Basic	108,221	101,826	96,068
Diluted	108,221	101,826	96,905