Condensed Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 27,027	$ 34,946
Marketable securities	148,143	151,663
Prepaid expenses and other current assets	8,432	8,182
Total current assets	183,602	194,791
Property and equipment, net	1,373	1,567
Operating lease, right-of-use ("ROU") asset	2,680	2,967
Other assets	320	320
Total assets	187,975	199,645
Current liabilities:
Accounts payable	1,125	3,382
Accrued expenses	8,943	11,690
Operating lease obligations, current portion	1,122	1,097
Total current liabilities	11,190	16,169
Operating lease obligations, long-term portion	1,520	1,838
Total liabilities	12,710	18,007
Commitments and contingencies (Note 7)
Stockholders' equity:
Common stock, $0.0001 par value: 300,000 shares authorized; 126,507 and 126,495 shares issued at March 31, 2023 and December 31, 2022, respectively; 126,375 and 126,302 shares outstanding at March 31, 2023 and December 31, 2022, respectively	13	13
Additional paid-in-capital	456,049	454,741
Accumulated other comprehensive loss	(146)	(302)
Accumulated deficit	(280,651)	(272,814)
Total stockholders' equity	175,265	181,638
Total liabilities and stockholders' equity	$ 187,975	$ 199,645