STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Balance (in shares) at Dec. 31, 2019		88,817,741
Balance at Dec. 31, 2019	$ 186,655	$ 9	$ 647,078	$ (460,452)	$ 20
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		169,931
Issuance of common stock under employee stock purchase plan	834		834
Issuance of common stock for services (in shares)		42,403
Issuance of common stock for services	310		310
Issuance of common stock upon exercise of options (in shares)		445,942
Issuance of common stock upon exercise of options	1,020		1,020
Issuance of common stock upon vesting of restricted stock units (in shares)		866,528
Issuance of common stock in at the market offering (in shares)		3,257,430
Issuance of common stock in at the market offering	21,047		21,047
Stock-based compensation	10,583		10,583
Unrealized losses on available-for-sale securities	(24)				(24)
Net loss	(94,313)			(94,313)
Balance (in shares) at Dec. 31, 2020		93,599,975
Balance at Dec. 31, 2020	126,112	$ 9	680,872	(554,765)	(4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		386,664
Issuance of common stock under employee stock purchase plan	819		819
Issuance of common stock for services (in shares)		25,989
Issuance of common stock for services	190		190
Issuance of common stock upon exercise of options (in shares)		331,310
Issuance of common stock upon exercise of options	584		584
Issuance of common stock upon vesting of restricted stock units (in shares)		167,158
Taxes paid for net share settlement of equity awards	(106)		(106)
Issuance of common stock in at the market offering (in shares)		35,671,439
Issuance of common stock in at the market offering	101,146	$ 4	101,142
Stock-based compensation	12,039		12,039
Unrealized losses on available-for-sale securities	(2)				(2)
Net loss	(158,165)			(158,165)
Balance (in shares) at Dec. 31, 2021		130,182,535
Balance at Dec. 31, 2021	82,617	$ 13	795,540	(712,930)	(6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock purchase plan (in shares)		308,356
Issuance of common stock under employee stock purchase plan	195		195
Issuance of common stock for services (in shares)		711,675
Issuance of common stock for services	$ 390		390
Issuance of common stock upon exercise of options (in shares)	14,000	14,080
Issuance of common stock upon exercise of options	$ 7		7
Issuance of common stock upon vesting of restricted stock units (in shares)		3,243,828
Issuance of common stock in at the market offering (in shares)		64,114,542
Issuance of common stock in at the market offering	71,625	$ 7	71,618
Stock-based compensation	10,750		10,750
Unrealized losses on available-for-sale securities	(48)				(48)
Net loss	(67,207)			(67,207)
Balance (in shares) at Dec. 31, 2022		198,575,016
Balance at Dec. 31, 2022	$ 98,329	$ 20	$ 878,500	$ (780,137)	$ (54)