CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	At-The-Market offering	Common Stock	Common Stock At-The-Market offering	Additional Paid-in Capital	Additional Paid-in Capital At-The-Market offering	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 53,739		$ 21		$ 319,115		$ 44	$ (265,441)
Beginning balance, shares at Dec. 31, 2019			20,851,531
Issuance of common stock upon exercise of options	40				40
Issuance of common stock upon exercise of options, shares			24,687
Issuance of common stock with restricted stock units and awards	58				58
Issuance of common stock with restricted stock units and awards, shares			34,265
Issuance of common stock for services	77				77
Issuance of common stock for services, shares			6,666
Stock-based compensation expense	1,370				1,370
Foreign currency translation adjustments	(71)						(71)
Net loss	(13,844)							(13,844)
Ending balance at Mar. 31, 2020	41,369		$ 21		320,660		(27)	(279,285)
Ending balance, shares at Mar. 31, 2020			20,917,149
Beginning balance at Dec. 31, 2019	53,739		$ 21		319,115		44	(265,441)
Beginning balance, shares at Dec. 31, 2019			20,851,531
Net loss	(34,318)
Ending balance at Sep. 30, 2020	128,576		$ 26		428,306		3	(299,759)
Ending balance, shares at Sep. 30, 2020			25,625,605
Beginning balance at Mar. 31, 2020	41,369		$ 21		320,660		(27)	(279,285)
Beginning balance, shares at Mar. 31, 2020			20,917,149
Issuance of common stock, net	93,827	$ 9,784	$ 4	$ 1	93,823	$ 9,783
Issuance of common stock, net, shares			3,852,500	511,648
Issuance of common stock under the Employee Stock Purchase Plan	359				359
Issuance of common stock under the Employee Stock Purchase Plan, shares			36,389
Issuance of common stock upon exercise of options	227				227
Issuance of common stock upon exercise of options, shares			99,206
Issuance of common stock upon exercise of warrants, shares			41,066
Issuance of common stock with restricted stock units and awards	53				53
Issuance of common stock with restricted stock units and awards, shares			31,114
Issuance of common stock for services	72				72
Issuance of common stock for services, shares			3,986
Stock-based compensation expense	1,305				1,305
Foreign currency translation adjustments	(4)						(4)
Net loss	(8,032)							(8,032)
Ending balance at Jun. 30, 2020	138,960		$ 26		426,282		(31)	(287,317)
Ending balance, shares at Jun. 30, 2020			25,493,058
Issuance of common stock upon exercise of options	217				217
Issuance of common stock upon exercise of options, shares			80,020
Issuance of common stock upon exercise of warrants, shares			16,208
Issuance of common stock for services	208				208
Issuance of common stock for services, shares			5,838
Issuance of restricted stock	51				51
Issuance of restricted stock, shares			30,481
Stock-based compensation expense	1,548				1,548
Foreign currency translation adjustments	34						34
Net loss	(12,442)							(12,442)
Ending balance at Sep. 30, 2020	128,576		$ 26		428,306		3	(299,759)
Ending balance, shares at Sep. 30, 2020			25,625,605
Beginning balance at Dec. 31, 2020	113,905		$ 26		430,781		41	(316,943)
Beginning balance, shares at Dec. 31, 2020			25,722,984
Issuance of common stock upon exercise of options	761				761
Issuance of common stock upon exercise of options, shares			77,892
Issuance of common stock with restricted stock units and awards	47				47
Issuance of common stock with restricted stock units and awards, shares			29,699
Issuance of common stock for services	110				110
Issuance of common stock for services, shares			3,633
Stock-based compensation expense	2,575				2,575
Foreign currency translation adjustments	11						11
Net loss	(10,407)							(10,407)
Ending balance at Mar. 31, 2021	107,002		$ 26		434,274		52	(327,350)
Ending balance, shares at Mar. 31, 2021			25,834,208
Beginning balance at Dec. 31, 2020	113,905		$ 26		430,781		41	(316,943)
Beginning balance, shares at Dec. 31, 2020			25,722,984
Net loss	(41,240)
Ending balance at Sep. 30, 2021	82,229		$ 26		440,367		19	(358,183)
Ending balance, shares at Sep. 30, 2021			26,043,578
Beginning balance at Mar. 31, 2021	107,002		$ 26		434,274		52	(327,350)
Beginning balance, shares at Mar. 31, 2021			25,834,208
Issuance of common stock under the Employee Stock Purchase Plan	851				851
Issuance of common stock under the Employee Stock Purchase Plan, shares			55,558
Issuance of common stock upon exercise of options	156				156
Issuance of common stock upon exercise of options, shares			14,577
Issuance of common stock with restricted stock units and awards	44				44
Issuance of common stock with restricted stock units and awards, shares			51,617
Issuance of common stock for services	13				13
Issuance of common stock for services, shares			545
Stock-based compensation expense	2,420				2,420
Foreign currency translation adjustments	7						7
Net loss	(17,267)							(17,267)
Ending balance at Jun. 30, 2021	93,226		$ 26		437,758		59	(344,617)
Ending balance, shares at Jun. 30, 2021			25,956,505
Issuance of common stock upon exercise of options	488				488
Issuance of common stock upon exercise of options, shares			61,594
Issuance of common stock with restricted stock units and awards	42				42
Issuance of common stock with restricted stock units and awards, shares			24,934
Issuance of common stock for services	13				13
Issuance of common stock for services, shares			545
Stock-based compensation expense	2,066				2,066
Foreign currency translation adjustments	(40)						(40)
Net loss	(13,566)							(13,566)
Ending balance at Sep. 30, 2021	$ 82,229		$ 26		$ 440,367		$ 19	$ (358,183)
Ending balance, shares at Sep. 30, 2021			26,043,578