CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 1,355	$ 828	$ 3,848	$ 2,058
Cost of sales	680	191	1,889	352
Gross profit	675	637	1,959	1,706
Costs and expenses:
Research and development	7,891	6,351	20,734	16,166
Sales, general and administrative	12,153	11,601	41,835	33,589
Total costs and expenses	20,044	17,952	62,569	49,755
Loss from operations	(19,369)	(17,315)	(60,610)	(48,049)
Other income (expense):
Interest expense	(3,357)	0	(6,720)	0
Foreign currency exchange loss	(133)	(40)	(331)	(73)
Interest income	908	323	1,983	612
Other income, net	0	2
Other (expense), net			(25)	(3)
Total other income (expense), net	(2,582)	285	(5,093)	536
Net loss before income taxes	(21,951)	(17,030)	(65,703)	(47,513)
Provision for income taxes	(147)	(45)	(432)	(220)
Net loss	$ (22,098)	$ (17,075)	$ (66,135)	$ (47,733)
Basic and diluted net loss per share (usd per share)	$ (0.41)	$ (0.31)	$ (1.21)	$ (0.89)
Weighted average shares outstanding (shares)	54,145	55,316	54,591	53,603
Other comprehensive loss:
Net loss	$ (22,098)	$ (17,075)	$ (66,135)	$ (47,733)
Net unrealized (loss) gain on available-for-sale investments	1	(7)	(54)	(4)
Foreign currency translation adjustment	(26)	91	(105)	295
Comprehensive loss	$ (22,123)	$ (16,991)	$ (66,294)	$ (47,442)