CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2020	$ 126,112	$ 9	$ 680,872	$ (554,765)	$ (4)
Beginning balance (shares) at Dec. 31, 2020		93,599,975
Issuance of common stock under employee stock purchase plan	478		478
Issuance of common stock under employee stock purchase plan (shares)		102,208
Issuance of common stock upon exercise of options	20		20
Issuance of common stock upon exercise of options (shares)		10,507
Issuance of common stock upon vesting of restricted stock units (shares)		35,100
Issuance of common stock in at the market offering	34,272	$ 1	34,271
Issuance of common stock in at the market offering (shares)		4,940,787
Stock-based compensation	3,087		3,087
Unrealized losses on available-for-sale securities	(3)				(3)
Net loss	(33,155)			(33,155)
Ending balance at Mar. 31, 2021	130,811	$ 10	718,728	(587,920)	(7)
Ending balance (shares) at Mar. 31, 2021		98,688,577
Beginning balance at Dec. 31, 2021	82,617	$ 13	795,540	(712,930)	(6)
Beginning balance (shares) at Dec. 31, 2021		130,182,535
Issuance of common stock under employee stock purchase plan	$ 83		83
Issuance of common stock under employee stock purchase plan (shares)		127,100
Issuance of common stock upon exercise of options (shares)	0
Issuance of common stock upon vesting of restricted stock units (shares)		113,469
Issuance of common stock in at the market offering	$ 5,921	$ 1	5,920
Issuance of common stock in at the market offering (shares)		5,907,256
Stock-based compensation	3,722		3,722
Unrealized losses on available-for-sale securities	(82)				(82)
Net loss	(28,071)			(28,071)
Ending balance at Mar. 31, 2022	$ 64,190	$ 14	$ 805,265	$ (741,001)	$ (88)
Ending balance (shares) at Mar. 31, 2022		136,330,360