Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 19,278	$ 34,946
Marketable securities	149,474	151,663
Prepaid expenses and other current assets	6,520	8,182
Total current assets	175,272	194,791
Property and equipment, net	1,204	1,567
Operating lease, right-of-use ("ROU") asset	2,385	2,967
Other assets	320	320
Total assets	179,181	199,645
Current liabilities:
Accounts payable	724	3,382
Accrued expenses	7,827	11,690
Operating lease obligations, current portion	1,147	1,097
Total current liabilities	9,698	16,169
Operating lease obligations, long-term portion	1,197	1,838
Total liabilities	10,895	18,007
Commitments and contingencies (Note 7)
Stockholders' equity:
Common stock, $0.0001 par value: 300,000 shares authorized; 127,459 and 126,495 shares issued at June 30, 2023 and December 31, 2022, respectively; 127,388 and 126,302 shares outstanding at June 30, 2023 and December 31, 2022, respectively	13	13
Additional paid-in-capital	460,709	454,741
Accumulated other comprehensive loss	(507)	(302)
Accumulated deficit	(291,929)	(272,814)
Total stockholders' equity	168,286	181,638
Total liabilities and stockholders' equity	$ 179,181	$ 199,645