Unaudited Condensed Consolidated Statement of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated  Deficit	Cumulative Translation  Adjustments
Beginning balance (in shares) at Dec. 31, 2019		59,562
Beginning balance at Dec. 31, 2019	$ 20,445	$ 60	$ 142,285	$ (121,900)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of offering costs (in shares)		1,225
Issuance of common stock, net of offering costs	4,856	$ 1	4,855
Exercise of stock options (in shares)		800
Exercise of stock options	2,859	$ 1	2,858
Share-based compensation	5,158		5,158
Translation adjustment	(3)				(3)
Net loss	(13,828)			(13,828)
Ending balance (in shares) at Sep. 30, 2020		61,587
Ending balance at Sep. 30, 2020	19,487	$ 62	155,156	(135,728)	(3)
Beginning balance (in shares) at Jun. 30, 2020		61,421
Beginning balance at Jun. 30, 2020	21,581	$ 61	153,036	(131,513)	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		166
Exercise of stock options	547	$ 1	546
Share-based compensation	1,574		1,574
Net loss	(4,215)			(4,215)
Ending balance (in shares) at Sep. 30, 2020		61,587
Ending balance at Sep. 30, 2020	19,487	$ 62	155,156	(135,728)	(3)
Beginning balance (in shares) at Dec. 31, 2020		61,881
Beginning balance at Dec. 31, 2020	16,424	$ 62	158,190	(141,825)	(3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of offering costs (in shares)		4,059
Issuance of common stock, net of offering costs	26,740	$ 4	26,736
Exercise of stock options (in shares)		2,154
Exercise of stock options	9,365	$ 2	9,363
Share-based compensation	4,722		4,722
Translation adjustment	1				1
Net loss	(21,803)			(21,803)
Ending balance (in shares) at Sep. 30, 2021		68,094
Ending balance at Sep. 30, 2021	35,449	$ 68	199,011	(163,628)	(2)
Beginning balance (in shares) at Jun. 30, 2021		68,009
Beginning balance at Jun. 30, 2021	42,142	$ 68	196,848	(154,772)	(2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		85
Exercise of stock options	341		341
Share-based compensation	1,822		1,822
Net loss	(8,856)			(8,856)
Ending balance (in shares) at Sep. 30, 2021		68,094
Ending balance at Sep. 30, 2021	$ 35,449	$ 68	$ 199,011	$ (163,628)	$ (2)