CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Series C Preferred Stock [Member]	Series A, B, C and D Convertible Preferred Stock [Member]	Series A, B, C and D Convertible Preferred Stock [Member] Series C Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Series C Preferred Stock [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Balances at Dec. 31, 2019	$ 74,574				$ 19	$ 273,966		$ (199,427)	$ 16
Balances, Shares at Dec. 31, 2019			2,720		19,190,695
Issuance of common stock upon the exercise of stock options	539					539
Issuance of common stock upon the exercise of stock options, shares					91,396
Issuance of common stock, net of financing/offering costs and net of issuance costs	8,955	$ 20,542			$ 1	8,954	$ 20,542
Issuance of common stock and preferred stock, net of financing/offering costs, shares				2,287	1,046,249
Beneficial conversion feature of Series C preferred stock				$ (549)			549
Deemed dividends related to immediate accretion of beneficial conversion feature of Series C preferred stock				$ 549			$ (549)
Share-based compensation expense	1,110					1,110
Unrealized gain on available-for-sale securities	(35)								(35)
Net loss	(23,258)							(23,258)
Balances at Mar. 31, 2020	82,427				$ 20	305,111		(222,685)	(19)
Balances, Shares at Mar. 31, 2020			5,007		20,328,340
Balances at Dec. 31, 2020	132,040		$ 3		$ 29	409,722		(277,707)	(7)
Balances, Shares at Dec. 31, 2020			3,218,287		29,260,247
Issuance of common stock upon the exercise of stock options	$ 93					93
Issuance of common stock upon the exercise of stock options, shares	11,514				11,514
Issuance of common stock, net of financing/offering costs and net of issuance costs	$ 4,123				$ 1	4,122
Issuance of common stock and preferred stock, net of financing/offering costs, shares					257,185
Conversion of convertible preferred stock to common stock, shares			(135)		135,000
Share-based compensation expense	2,009					2,009
Unrealized gain on available-for-sale securities	4								4
Net loss	(19,423)							(19,423)
Balances at Mar. 31, 2021	$ 118,846		$ 3		$ 30	$ 415,946		$ (297,130)	$ (3)
Balances, Shares at Mar. 31, 2021			3,218,152		29,663,946