Note 9 - Stockholders' Equity - Shares of Common Stock Reserved for Issuance (Details) - shares	Jun. 30, 2024	Feb. 27, 2024	Dec. 31, 2023
Common stock reserved for issuance (in shares)	45,688,228		27,043,664
Common Warrants [Member]
Common stock reserved for issuance (in shares)	140,596		227,434
The 2019 Plan [Member]
Common stock reserved for issuance (in shares)	16,621,469		5,685,806
The 2024 Inducement Award Plan [Member]
Common stock reserved for issuance (in shares)	1,727,500	3,000,000	0
Share-Based Payment Arrangement, Option [Member]
Common stock reserved for issuance (in shares)	21,699,803		17,938,726
Restricted Stock Units (RSUs) [Member]
Common stock reserved for issuance (in shares)	3,135,958		2,126,373
ESPP [Member]
Common stock reserved for issuance (in shares)	2,362,902		1,065,325