CONDENSED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated deficit	Convertible preferred stock Preferred Stock
Beginning balance (in shares) at Dec. 31, 2020		67,432,712			1,931,860
Beginning balance at Dec. 31, 2020	$ 26,026	$ 67	$ 453,002	$ (427,045)	$ 2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon vesting of restricted stock units (in shares)		16,902
Issuance of common stock upon exercise of options (in shares)		26,770
Issuance of common stock upon exercise of options	26		26
Issuance of common stock upon exercise of warrants (in shares)		2,418,681
Issuance of common stock upon exercise of warrants	666	$ 3	663
Issuance of common stock through ATM (in shares)		4,009,585
Issuance of common stock through ATM	5,713	$ 4	5,709
Issuance of common stock under Employee Stock Purchase Plan (in shares)		4,122
Issuance of common stock under Employee Stock Purchase Plan	2		2
Conversions of convertible preferred stock (in shares)		780,360			(78,036)
Conversions of convertible preferred stock	0	$ 1	(1)
Stock-based compensation expense	691		691
Net loss	(6,013)			(6,013)
Ending balance (in shares) at Mar. 31, 2021		74,689,132			1,853,824
Ending balance at Mar. 31, 2021	27,111	$ 75	460,092	(433,058)	$ 2
Beginning balance (in shares) at Dec. 31, 2021		145,971,184			5,571,959
Beginning balance at Dec. 31, 2021	54,958	$ 146	509,660	(454,853)	$ 5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under Employee Stock Purchase Plan (in shares)		9,996
Issuance of common stock under Employee Stock Purchase Plan	2		2
Stock-based compensation expense	1,000		1,000
Net loss	(6,719)			(6,719)
Ending balance (in shares) at Mar. 31, 2022		145,981,180			5,571,959
Ending balance at Mar. 31, 2022	$ 49,241	$ 146	$ 510,662	$ (461,572)	$ 5