STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Deficit
Balance at Dec. 31, 2019	$ 95,010	$ 182	$ 778,953	$ (684,125)
Balance (in shares) at Dec. 31, 2019		181,803,320
Stock-based compensation	1,940		1,940
Exercise of employee stock options	4		4
Exercise of employee stock options (in shares)		2,333
Issuance of common stock in connection with a public offering, net	88,661	$ 29	88,632
Issuance of common stock in connection with a public offering, net (in shares)		29,110,111
Issuance of common stock in connection with at the market offering, net	13,015	$ 2	13,013
Issuance of common stock in connection with at the market offering, net (in shares)		2,814,673
Net loss	(18,293)			(18,293)
Issuance of restricted common stock		$ 1	(1)
Issuance of restricted common stock (in shares)		555,900
Balance at Mar. 31, 2020	180,337	$ 214	882,541	(702,418)
Balance (in shares) at Mar. 31, 2020		214,286,337
Balance at Dec. 31, 2020	123,982	$ 215	887,868	(764,101)
Balance (in shares) at Dec. 31, 2020		214,591,906
Stock-based compensation	2,197		2,197
Exercise of employee stock options	$ 1,016		1,016
Exercise of employee stock options (in shares)	352,442	352,442
Restricted stock awards (in shares)		313,326
Net loss	$ (21,554)			(21,554)
Balance at Mar. 31, 2021	$ 105,641	$ 215	$ 891,081	$ (785,655)
Balance (in shares) at Mar. 31, 2021		215,257,674