Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 103,868	$ 110,890
Restricted cash	110	110
Prepaid expenses	5,295	4,031
Research and development tax rebate receivable	738	743
Other current assets	858	2,423
Total current assets	110,869	118,197
Investment in equity securities	4,700	4,700
Other assets	631	635
Total assets	116,200	123,532
Current liabilities
Accounts payable	1,444	2,965
Accrued expenses	613	1,059
Payroll liabilities	822	1,525
Other current liabilities	65	19
Total current liabilities	2,944	5,568
Total liabilities	2,944	5,568
Commitments and contingencies (Note 14)
Stockholders' equity
Series B convertible preferred stock - $0.001 par value; 10,000 shares authorized; 1 shares issued and outstanding as of March 31, 2023 and December 31, 2022	0	0
Common stock - $0.18 par value; 175,000 shares authorized; 126,624 shares issued and outstanding as of March 31, 2023 and December 31, 2022	22,792	22,792
Additional paid-in capital - common stock	252,357	250,784
Accumulated deficit	(162,475)	(156,194)
Total stockholders' equity	113,256	117,964
Total liabilities and stockholders' equity	116,200	123,532
Series B Preferred Stock [Member]
Stockholders' equity
Additional paid-in capital - Series B convertible preferred stock	$ 582	$ 582