CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Net sales	$ 11,782	$ 11,165	$ 9,297
Cost of Goods and Services Sold [Abstract]
Cost of sales of products and services	7,663	6,706	4,897
Inventory write-down	4,500	0	0
Cost of sales of products and services	12,163	6,706	4,897
Gross (loss) profit	(381)	4,459	4,400
Costs and expenses:
Research and development	21,943	21,255	25,345
Sales, general and administrative	49,236	46,904	51,886
Total costs and expenses	71,179	68,159	77,231
Loss from operations	(71,560)	(63,700)	(72,831)
Other income (expense):
Interest expense	(15,545)	(15,550)	(14,256)
Gain on extinguishment of debt	9,793	0	0
Foreign currency exchange (loss) gain	(413)	252	(124)
Interest and dividend income	88	855	2,809
Other expense, net	(20)	(60)	(14)
Total other expense, net	(6,097)	(14,503)	(11,585)
Net loss before income taxes	(77,657)	(78,203)	(84,416)
(Provision) benefit for income taxes	(45)	(5)	111
Net loss	$ (77,702)	$ (78,208)	$ (84,305)
Basic net loss per share (dollars per share)	$ (1.26)	$ (1.40)	$ (1.55)
Diluted net loss per share (dollars per share)	$ (1.26)	$ (1.40)	$ (1.55)
Weighted average shares outstanding, basic (shares)	61,727	56,010	54,506
Weighted average shares outstanding, diluted (shares)	61,727	56,010	54,506
Other comprehensive loss:
Net loss	$ (77,702)	$ (78,208)	$ (84,305)
Net unrealized (loss) gain on investments	(34)	(2)	193
Foreign currency translation adjustment	(117)	151	(102)
Comprehensive loss	$ (77,853)	$ (78,059)	$ (84,214)