Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common stock Public offering	Common stock At-the-market sales	Common stock	Additional Paid in Capital. Public offering	Additional Paid in Capital. At-the-market sales	Additional Paid in Capital.	Accumulated Other Comprehensive Income	Accumulated Deficit	Public offering	At-the-market sales	Total
Balance at Dec. 31, 2019			$ 7			$ 306,108		$ (260,370)			$ 45,745
Balance (in shares) at Dec. 31, 2019			69,810,305
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						621					621
Issuance of common stock	$ 2			$ 48,433					$ 48,435
Issuance of common stock (in shares)	17,250,000
Issuance of common stock upon exercise of options						119					119
Issuance of common stock upon exercise of options (in shares)			152,907
Warrants issued in connection with long-term debt						3,570					3,570
Net loss								(7,883)			(7,883)
Balance at Mar. 31, 2020			$ 9			358,851		(268,253)			90,607
Balance (in shares) at Mar. 31, 2020			87,213,212
Balance at Dec. 31, 2019			$ 7			306,108		(260,370)			45,745
Balance (in shares) at Dec. 31, 2019			69,810,305
Increase (decrease) in stockholders' equity
Unrealized net gain on marketable securities											11
Net loss											(34,233)
Balance at Sep. 30, 2020			$ 9			360,713	$ 11	(294,603)			66,130
Balance (in shares) at Sep. 30, 2020			87,434,604
Balance at Mar. 31, 2020			$ 9			358,851		(268,253)			90,607
Balance (in shares) at Mar. 31, 2020			87,213,212
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						839					839
Issuance of common stock upon exercise of options						166					166
Issuance of common stock upon exercise of options (in shares)			84,393
Unrealized net gain on marketable securities							10				10
Net loss								(10,826)			(10,826)
Balance at Jun. 30, 2020			$ 9			359,856	10	(279,079)			80,796
Balance (in shares) at Jun. 30, 2020			87,297,605
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						647					647
Issuance of common stock upon exercise of options						210					210
Issuance of common stock upon exercise of options (in shares)			136,999
Unrealized net gain on marketable securities							1				1
Net loss								(15,524)			(15,524)
Balance at Sep. 30, 2020			$ 9			360,713	11	(294,603)			66,130
Balance (in shares) at Sep. 30, 2020			87,434,604
Balance at Dec. 31, 2020			$ 9			361,539	3	(312,223)			49,328
Balance (in shares) at Dec. 31, 2020			87,563,753
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						742					742
Issuance of common stock					$ 960					$ 960
Issuance of common stock (in shares)		520,937
Issuance of common stock upon exercise of options						75					75
Issuance of common stock upon exercise of options (in shares)			126,400
Vesting of RSUs (in shares)			52,651
Warrants issued in connection with long-term debt						1,080					1,080
Unrealized net gain on marketable securities							(3)				(3)
Net loss								(17,128)			(17,128)
Balance at Mar. 31, 2021			$ 9			364,396		(329,351)			35,054
Balance (in shares) at Mar. 31, 2021			88,263,741
Balance at Dec. 31, 2020			$ 9			361,539	$ 3	(312,223)			49,328
Balance (in shares) at Dec. 31, 2020			87,563,753
Increase (decrease) in stockholders' equity
Issuance of common stock (in shares)		6,915,151
Unrealized net gain on marketable securities											(3)
Net loss											(51,537)
Balance at Sep. 30, 2021			$ 9			374,431		(363,760)			10,680
Balance (in shares) at Sep. 30, 2021			94,729,385
Balance at Mar. 31, 2021			$ 9			364,396		(329,351)			35,054
Balance (in shares) at Mar. 31, 2021			88,263,741
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						843					843
Issuance of common stock					6,349					6,349
Issuance of common stock (in shares)		4,593,034
Vesting of RSUs (in shares)			71,430
Net loss								(17,637)			(17,637)
Balance at Jun. 30, 2021			$ 9			371,588		(346,988)			24,609
Balance (in shares) at Jun. 30, 2021			92,928,205
Increase (decrease) in stockholders' equity
Share-based compensation - stock options and RSUs						887					887
Issuance of common stock					$ 1,956					$ 1,956
Issuance of common stock (in shares)		1,801,180
Net loss								(16,772)			(16,772)
Balance at Sep. 30, 2021			$ 9			$ 374,431		$ (363,760)			$ 10,680
Balance (in shares) at Sep. 30, 2021			94,729,385