Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2019	$ 2	$ 167,149	$ (148,662)	$ 18,489
Balance (in shares) at Dec. 31, 2019	18,081,753
Increase (Decrease) in Stockholders' Equity
Issuance of common stock under stock incentive plans		315		315
Issuance of common stock under stock incentive plans (in shares)	88,375
Stock-based compensation expense		805		805
Issuance of common stock in at-the-market offering, net of issuance costs		2,084		2,084
Issuance of common stock in at-the-market offering, net of issuance costs (in shares)	468,427
Net loss			(1,732)	(1,732)
Balance at Mar. 31, 2020	$ 2	170,353	(150,394)	19,961
Balance (in shares) at Mar. 31, 2020	18,638,555
Balance at Dec. 31, 2020	$ 2	174,584	(157,174)	17,412
Balance (in shares) at Dec. 31, 2020	19,031,556
Increase (Decrease) in Stockholders' Equity
Exercise of stock options		144		$ 144
Exercise of stock options (in shares)	54,077			54,077
Issuance of common stock under stock incentive plans		364		$ 364
Issuance of common stock under stock incentive plans (in shares)	136,709
Stock-based compensation expense		743		743
Net loss			(460)	(460)
Balance at Mar. 31, 2021	$ 2	$ 175,835	$ (157,634)	$ 18,203
Balance (in shares) at Mar. 31, 2021	19,222,342