Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 30,426	$ 34,946
Marketable securities	133,277	151,663
Prepaid expenses and other current assets	2,881	8,182
Total current assets	166,584	194,791
Property and equipment, net	1,051	1,567
Operating lease, right-of-use ("ROU") asset	2,083	2,967
Other assets	320	320
Total assets	170,038	199,645
Current liabilities:
Accounts payable	2,306	3,382
Accrued expenses	5,644	11,690
Operating lease obligations, current portion	1,174	1,097
Total current liabilities	9,124	16,169
Operating lease obligations, long-term portion	869	1,838
Total liabilities	9,993	18,007
Commitments and Contingencies
Stockholders' equity:
Common stock, $0.0001 par value: 300,000 shares authorized; 127,476 and 126,495 shares issued at September 30, 2023 and December 31, 2022, respectively; 127,445 and 126,302 shares outstanding at September 30, 2023 and December 31, 2022, respectively	13	13
Additional paid-in-capital	462,355	454,741
Accumulated other comprehensive loss	(430)	(302)
Accumulated deficit	(301,893)	(272,814)
Total stockholders' equity	160,045	181,638
Total liabilities and stockholders' equity	$ 170,038	$ 199,645