Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Gain	Total
Balance at Dec. 31, 2018	$ 7	$ 232,243	$ (197,304)	$ (4)	$ 34,942
Balance (in shares) at Dec. 31, 2018	7,141,996
Increase (Decrease) in Shareholders' Equity
Issuance of common stock and warrants in public offerings, net of issuance costs	$ 4	18,501			18,505
Issuance of common stock and warrants in public offerings, net of issuance costs (in shares)	4,000,000
Issuance of common stock for at-the-market offerings, net of issuance costs	$ 1	6,995			6,996
Issuance of common stock for at-the-market offerings, net of issuance costs of (in shares)	1,282,904
Proceeds from exercises of warrants		54			54
Proceeds from exercises of warrants (in shares)	8,700
Stock-based compensation expense		1,512			1,512
Unrealized gain on short-term investments				$ 4	4
Net loss			(26,293)		(26,293)
Balance at Dec. 31, 2019	$ 12	259,305	(223,597)		$ 35,720
Balance (in shares) at Dec. 31, 2019	12,433,600				12,433,600
Increase (Decrease) in Shareholders' Equity
Issuance of common stock and warrants in public offerings, net of issuance costs	$ 5	24,554			$ 24,559
Issuance of common stock and warrants in public offerings, net of issuance costs (in shares)	5,290,000
Issuance of common stock for at-the-market offerings, net of issuance costs	$ 3	16,267			16,270
Issuance of common stock for at-the-market offerings, net of issuance costs of (in shares)	2,353,737
Proceeds from exercises of warrants		31			31
Proceeds from exercises of warrants (in shares)	7,000
Stock-based compensation expense		1,389			1,389
Net loss			(37,300)		(37,300)
Balance at Dec. 31, 2020	$ 20	$ 301,546	$ (260,897)		$ 40,669
Balance (in shares) at Dec. 31, 2020	20,084,337				20,084,337