CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Series A Convertible Preferred Stock Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance at Dec. 31, 2019		$ 22	$ 295,056			$ (235,574)	$ 59,569
Balance (in shares) at Dec. 31, 2019		21,625,088		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense			1,876				1,876
Exercise of stock options			312				312
Exercise of stock options (in shares)		59,978
Issuance of restricted stock (in shares)		5,250
Deemed dividend on beneficial conversion feature - Series A convertible preferred stock			8,880			(8,880)
Unrealized gain (loss) on investments					$ 28		28
Net loss						(18,672)	(18,672)
Balance at Mar. 31, 2020		$ 22	306,124		$ 28	(263,126)	43,113
Balance (in shares) at Mar. 31, 2020		21,690,316		7,307
Balance at Dec. 31, 2020	$ 4,469	$ 37	444,622			(311,929)	137,199
Balance (in shares) at Dec. 31, 2020	4,753	36,585,767		7,307
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense			5,035				5,035
Exercise of stock options			244				244
Exercise of stock options (in shares)		55,030
Financing costs under equity distribution agreement			(3)				(3)
Net loss						(27,141)	(27,141)
Balance at Mar. 31, 2021	$ 4,469	$ 37	$ 449,898			$ (339,070)	$ 115,334
Balance (in shares) at Mar. 31, 2021	4,753	36,640,797		7,307