Note 9 - Stockholders' Equity - Shares of Common Stock Reserved for Issuance (Details) - shares	Sep. 30, 2023	Dec. 31, 2022
Common stock reserved for issuance (in shares)	28,922,321	29,635,697
Common Warrants [Member]
Common stock reserved for issuance (in shares)	227,434	227,434
Share-Based Payment Arrangement, Option [Member]
Common stock reserved for issuance (in shares)	18,073,909	14,725,261
Restricted Stock Units (RSUs) [Member]
Common stock reserved for issuance (in shares)	3,594,698	808,310
Future Grants of Equity Awards [Member]
Common stock reserved for issuance (in shares)	5,527,341	12,074,692
ESPP [Member]
Common stock reserved for issuance (in shares)	1,498,939	1,800,000