CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Net sales	$ 1,806	$ 1,692	$ 3,557	$ 2,493
Cost of sales	907	717	1,823	1,210
Gross profit	899	975	1,734	1,283
Costs and expenses:
Research and development	6,149	6,060	13,083	12,842
Sales, general and administrative	12,837	15,330	25,559	29,682
Total costs and expenses	18,986	21,390	38,642	42,524
Loss from operations	(18,087)	(20,415)	(36,908)	(41,241)
Other income (expense):
Interest expense	(3,528)	(3,205)	(6,987)	(3,363)
Foreign currency exchange gain (loss)	6	(253)	(53)	(198)
Interest income	812	774	1,653	1,075
Other expense, net	(1)	(25)	(3)	(25)
Total other expense, net	(2,711)	(2,709)	(5,390)	(2,511)
Net loss before income taxes	(20,798)	(23,124)	(42,298)	(43,752)
Provision for income taxes	(17)	(101)	(238)	(285)
Net loss	$ (20,815)	$ (23,225)	$ (42,536)	$ (44,037)
Basic and diluted net loss per share (usd per share)	$ (0.38)	$ (0.43)	$ (0.78)	$ (0.80)
Weighted average shares outstanding (shares)	54,476	54,003	54,407	54,821
Other comprehensive loss:
Net loss	$ (20,815)	$ (23,225)	$ (42,536)	$ (44,037)
Net unrealized gain (loss) on available-for-sale investments	98	(2)	219	(55)
Foreign currency translation adjustment	50	(191)	(26)	(79)
Comprehensive loss	$ (20,667)	$ (23,418)	$ (42,343)	$ (44,171)