Note 9 - Stockholders' Equity - Shares of Common Stock Reserved for Issuance (Details) - shares	Jun. 30, 2022	Dec. 31, 2021
Common stock reserved for issuance (in shares)	15,945,390	16,031,282
Common Warrants [Member]
Common stock reserved for issuance (in shares)	227,434	232,434
Share-Based Payment Arrangement, Option [Member]
Common stock reserved for issuance (in shares)	14,305,918	10,216,106
Restricted Stock Units (RSUs) [Member]
Common stock reserved for issuance (in shares)	507,472	0
Future Grants of Equity Awards [Member]
Common stock reserved for issuance (in shares)	904,566	5,582,742