CONDENSED CONSOLIDATEDSTATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales	$ 1,692	$ 699	$ 2,493	$ 1,230
Cost of sales	717	135	1,210	161
Gross profit	975	564	1,283	1,069
Costs and expenses:
Research and development	6,060	5,527	12,842	9,815
Sales, general and administrative	15,330	11,460	29,682	21,988
Total costs and expenses	21,390	16,987	42,524	31,803
Loss from operations	(20,415)	(16,423)	(41,241)	(30,734)
Other income (expense):
Interest expense	(3,205)	0	(3,363)	0
Foreign currency exchange (loss)	(253)	(7)	(198)	(33)
Interest income	774	153	1,075	290
Other expense, net	(25)	(5)	(25)	(5)
Total other income (expense), net	(2,709)	141	(2,511)	252
Net loss before income taxes	(23,124)	(16,282)	(43,752)	(30,482)
Provision for income taxes	(101)	(175)	(285)	(175)
Net loss	$ (23,225)	$ (16,457)	$ (44,037)	$ (30,657)
Basic and diluted net loss per share (usd per share)	$ (0.43)	$ (0.31)	$ (0.80)	$ (0.58)
Weighted average shares outstanding (shares)	54,003	53,568	54,821	52,732
Other comprehensive loss:
Net loss	$ (23,225)	$ (16,457)	$ (44,037)	$ (30,657)
Net unrealized (loss) gain on available-for-sale investments	(2)	3	(55)	3
Foreign currency translation adjustment	(191)	204	(79)	204
Comprehensive loss	$ (23,418)	$ (16,250)	$ (44,171)	$ (30,450)