Consolidated Statements of Changes in Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Private Placement	Common stock	Common stock Private Placement	Additional paid-In Capital	Additional paid-In Capital Private Placement	Accumulated deficit	Accumulated other comprehensive loss
Beginning balance (in shares) at Dec. 31, 2018			22,471,776
Beginning balance at Dec. 31, 2018	$ (5,418)		$ 3		$ 279,539		$ (280,403)	$ (4,557)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)			11,943
Issuance of common stock under Employee Stock Purchase Plan	20				20
Issuance of common stock upon exercise of options (in shares)			115,600
Issuance of common stock upon exercise of options	145				145
Stock-based compensation expense	1,180				1,180
Foreign currency translation adjustment	22							22
Net loss	(12,074)						(12,074)
Issuance of common stock, net of issuance costs (in shares)			22,188,706
Issuance of common stock, net	30,942		$ 2		30,940
Unrealized gain on securities	2							2
Ending balance (in shares) at Mar. 31, 2019			44,788,025
Ending balance at Mar. 31, 2019	14,819		$ 5		311,824		(292,477)	(4,533)
Beginning balance (in shares) at Dec. 31, 2018			22,471,776
Beginning balance at Dec. 31, 2018	(5,418)		$ 3		279,539		(280,403)	(4,557)
Increase (Decrease) in Stockholders' Equity
Foreign currency translation adjustment	24
Net loss	(40,462)
Unrealized gain on securities	0
Ending balance (in shares) at Sep. 30, 2019			48,196,387
Ending balance at Sep. 30, 2019	(4,915)		$ 5		320,478		(320,865)	(4,533)
Beginning balance (in shares) at Mar. 31, 2019			44,788,025
Beginning balance at Mar. 31, 2019	14,819		$ 5		311,824		(292,477)	(4,533)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock through at-the-market offering, net (in shares)			164,926
Issuance of common stock through at-the-market offering, net	372				372
Stock-based compensation expense	1,251				1,251
Foreign currency translation adjustment	7							7
Net loss	(16,394)						(16,394)
Unrealized gain on securities	1							1
Ending balance (in shares) at Jun. 30, 2019			44,952,951
Ending balance at Jun. 30, 2019	56		$ 5		313,447		(308,871)	(4,525)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)			5,262
Issuance of common stock under Employee Stock Purchase Plan	8				8
Issuance of common stock upon exercise of options (in shares)			10,000
Issuance of common stock upon exercise of options	5				5
Issuance of vested restricted stock units (in shares)			50,000
Issuance of vested restricted stock units	0
Stock-based compensation expense	1,303				1,303
Foreign currency translation adjustment	(5)							(5)
Net loss	(11,994)						(11,994)
Issuance of common stock, net of issuance costs (in shares)				3,178,174
Issuance of common stock, net		$ 5,715				$ 5,715
Unrealized gain on securities	(3)							(3)
Ending balance (in shares) at Sep. 30, 2019			48,196,387
Ending balance at Sep. 30, 2019	$ (4,915)		$ 5		320,478		(320,865)	(4,533)
Beginning balance (in shares) at Dec. 31, 2019	86,325,547		86,325,547
Beginning balance at Dec. 31, 2019	$ 8,397		$ 9		348,664		(335,753)	(4,523)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)			78,583
Issuance of common stock under Employee Stock Purchase Plan	114				114
Issuance of common stock upon exercise of options (in shares)			5,128
Issuance of common stock upon exercise of options	3				3
Issuance of vested restricted stock units (in shares)			10,937
Issuance of common stock through at-the-market offering, net (in shares)			598,977
Issuance of common stock through at-the-market offering, net	1,141				1,141
Other financing fees	(147)				(147)
Stock-based compensation expense	1,409				1,409
Foreign currency translation adjustment	(60)							(60)
Net loss	(19,620)						(19,620)
Ending balance (in shares) at Mar. 31, 2020			87,019,172
Ending balance at Mar. 31, 2020	$ (8,763)		$ 9		351,184		(355,373)	(4,583)
Beginning balance (in shares) at Dec. 31, 2019	86,325,547		86,325,547
Beginning balance at Dec. 31, 2019	$ 8,397		$ 9		348,664		(335,753)	(4,523)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of common warrants (in shares)	17,734,573,000		5,176,973
Foreign currency translation adjustment	$ (61)
Net loss	(53,430)
Unrealized gain on securities	$ 0
Ending balance (in shares) at Sep. 30, 2020	107,235,976		107,235,976
Ending balance at Sep. 30, 2020	$ (7,382)		$ 11		386,374		(389,183)	(4,584)
Beginning balance (in shares) at Mar. 31, 2020			87,019,172
Beginning balance at Mar. 31, 2020	(8,763)		$ 9		351,184		(355,373)	(4,583)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of options (in shares)			37,500
Issuance of common stock upon exercise of options	98				98
Issuance of vested restricted stock units (in shares)			10,938
Issuance of common stock through at-the-market offering, net (in shares)			470,509
Issuance of common stock through at-the-market offering, net	967				967
Issuance of common stock upon exercise of pre-funded warrants (in shares)			8,342,128
Issuance of common stock upon exercise of pre-funded warrants	1		$ 1
Issuance of common stock upon exercise of common warrants (in shares)			4,967,563
Issuance of common stock upon exercise of common warrants	17,214				17,214
Stock-based compensation expense	1,481				1,481
Foreign currency translation adjustment	31							31
Net loss	(24,081)						(24,081)
Ending balance (in shares) at Jun. 30, 2020			100,847,810
Ending balance at Jun. 30, 2020	(13,052)		$ 10		370,944		(379,454)	(4,552)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under Employee Stock Purchase Plan (in shares)			31,629
Issuance of common stock under Employee Stock Purchase Plan	70				70
Issuance of vested restricted stock units (in shares)			60,937
Issuance of common stock upon exercise of common warrants (in shares)			879,210
Issuance of common stock upon exercise of common warrants	3,485		$ 0		3,485
Other financing fees	(133)				(133)
Stock-based compensation expense	1,296				1,296
Foreign currency translation adjustment	(32)							(32)
Net loss	(9,729)						(9,729)
Issuance of common stock, net of issuance costs (in shares)				5,416,390
Issuance of common stock, net		10,269		$ 1		10,268
Issuance of common warrants with long-term debt, net		$ 444				$ 444
Unrealized gain on securities	$ 0
Ending balance (in shares) at Sep. 30, 2020	107,235,976		107,235,976
Ending balance at Sep. 30, 2020	$ (7,382)		$ 11		$ 386,374		$ (389,183)	$ (4,584)