Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2019	48,503	10,364,663
Balance at Dec. 31, 2019	$ 0	$ 10	$ 355,220	$ (348,335)	$ 6,895
Issuance of common stock in public offerings, net of commissions and issuance costs (in shares)	0	74,140,297
Issuance of common stock in public offerings, net of commissions and issuance costs	$ 0	$ 74	23,574	0	23,648
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units (in shares)	0	416,119
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units	$ 0	$ 1	27	0	28
Employee stock-based compensation	0	0	1,160	0	1,160
Accretion of Series A preferred stock dividends	0	0	(2,901)	0	(2,901)
Net and comprehensive loss	$ 0	$ 0	0	(14,376)	(14,376)
Balance (in shares) at Sep. 30, 2020	48,503	84,921,079
Balance at Sep. 30, 2020	$ 0	$ 85	377,080	(362,711)	14,454
Balance (in shares) at Jun. 30, 2020	48,503	51,339,024
Balance at Jun. 30, 2020	$ 0	$ 51	365,684	(358,186)	7,549
Issuance of common stock in public offerings, net of commissions and issuance costs (in shares)	0	33,221,725
Issuance of common stock in public offerings, net of commissions and issuance costs	$ 0	$ 33	11,979	0	12,012
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units (in shares)	0	360,330
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units	$ 0	$ 1	0	0	1
Employee stock-based compensation	0	0	384	0	384
Accretion of Series A preferred stock dividends	0	0	(967)	0	(967)
Net and comprehensive loss	$ 0	$ 0	0	(4,525)	(4,525)
Balance (in shares) at Sep. 30, 2020	48,503	84,921,079
Balance at Sep. 30, 2020	$ 0	$ 85	377,080	(362,711)	14,454
Balance (in shares) at Dec. 31, 2020	52,369	84,926,129
Balance at Dec. 31, 2020	$ 0	$ 85	380,332	(367,341)	13,076
Issuance of common stock in public offerings, net of commissions and issuance costs (in shares)	0	10,000,000
Issuance of common stock in public offerings, net of commissions and issuance costs	$ 0	$ 10	13,067	0	13,077
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units (in shares)	0	264,826
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units	$ 0	$ 1	0	0	1
Employee stock-based compensation	0	0	960	0	960
Accretion of Series A preferred stock dividends	0	0	(3,132)	0	(3,132)
Net and comprehensive loss	$ 0	$ 0	0	(12,416)	(12,416)
Conversion of Series B preferred stock into common stock (in shares)	(93)	372,000
Conversion of Series B preferred stock into common stock	$ 0	$ 0	0	0	0
Balance (in shares) at Sep. 30, 2021	52,276	95,562,955
Balance at Sep. 30, 2021	$ 0	$ 96	391,227	(379,757)	11,566
Balance (in shares) at Jun. 30, 2021	52,276	95,353,002
Balance at Jun. 30, 2021	$ 0	$ 95	392,032	(374,845)	17,282
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units (in shares)	0	209,953
Issuance of common stock under officers and directors purchase plan and vesting of restricted stock units	$ 0	$ 1	0	0	1
Employee stock-based compensation	0	0	239	0	239
Accretion of Series A preferred stock dividends	0	0	(1,044)	0	(1,044)
Net and comprehensive loss	$ 0	$ 0	0	(4,912)	(4,912)
Balance (in shares) at Sep. 30, 2021	52,276	95,562,955
Balance at Sep. 30, 2021	$ 0	$ 96	$ 391,227	$ (379,757)	$ 11,566