Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 31,598	$ 27,142
Prepaid expenses and other current assets	1,736	2,323
Total current assets	33,334	29,465
Other assets	71	135
Total assets	33,405	29,600
Current liabilities:
Accounts payable	924	1,292
Accrued expenses and other	5,065	4,042
Accrued dividends payable	65	65
Total current liabilities	6,054	5,399
Convertible note payable and accrued interest, net of debt discount – related party (Note 4)	9,643	0
Derivative liability (Note 4)	592	0
Other liabilities	0	8
Total liabilities	16,289	5,407
Commitments and contingencies (Note 10)
Stockholders' equity:
Undesignated stock, $0.01 par value; 20,000,000 shares authorized, 20,000,000 designated at June 30, 2021 and December 31, 2020, respectively
Common stock, $0.001 par value; 100,000,000 shares authorized at June 30, 2021 and December 31, 2020, 59,275,031 and 57,077,055 issued and outstanding at June 30, 2021 and December 31, 2020, respectively	59	56
Additional paid-in capital	269,657	261,883
Retained deficit	(254,850)	(239,996)
Total stockholders' equity	15,393	22,470
Total liabilities, redeemable convertible preferred stock and stockholders' equity	33,405	29,600
Series C super dividend redeemable convertible preferred stock
Current liabilities:
Convertible preferred stock, value	1,723	1,723
Series A 12% convertible preferred stock
Stockholders' equity:
Convertible preferred stock, value	$ 527	$ 527