CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net sales	$ 2,798,000	$ 2,125,000	$ 5,316,000	$ 4,468,000
Cost of sales	1,745,000	1,171,000	3,365,000	2,459,000
Gross profit	1,053,000	954,000	1,951,000	2,009,000
Costs and expenses:
Research and development	5,733,000	5,347,000	12,629,000	11,189,000
Sales, general and administrative	12,910,000	11,332,000	26,938,000	24,275,000
Total costs and expenses	18,643,000	16,679,000	39,567,000	35,464,000
Loss from operations	(17,590,000)	(15,725,000)	(37,616,000)	(33,455,000)
Other income (expense):
Interest expense	(4,177,000)	(3,835,000)	(8,267,000)	(7,584,000)
Foreign currency exchange gain (loss)	0	91,000	(159,000)	(37,000)
Interest income	12,000	224,000	55,000	604,000
Other income (expense), net	81,000	15,000	74,000	(67,000)
Total other expense, net	(4,084,000)	(3,505,000)	(8,297,000)	(7,084,000)
Net loss before income taxes	(21,674,000)	(19,230,000)	(45,913,000)	(40,539,000)
Provision for income taxes	0	0	0	0
Net loss	$ (21,674,000)	$ (19,230,000)	$ (45,913,000)	$ (40,539,000)
Basic net loss per share (usd per share)	$ (0.36)	$ (0.35)	$ (0.77)	$ (0.74)
Diluted net loss per share (usd per share)	$ (0.36)	$ (0.35)	$ (0.77)	$ (0.74)
Weighted average shares outstanding basic (shares)	61,049	55,445	59,790	55,139
Weighted average shares outstanding diluted (shares)	61,049	55,445	59,790	55,139
Other comprehensive loss:
Net loss	$ (21,674,000)	$ (19,230,000)	$ (45,913,000)	$ (40,539,000)
Net unrealized (loss) gain on debt securities available-for-sale	1,000	(44,000)	(18,000)	179,000
Foreign currency translation adjustment	21,000	34,000	(60,000)	19,000
Comprehensive loss	$ (21,652,000)	$ (19,240,000)	$ (45,991,000)	$ (40,341,000)