Note 12 - Stockholders' Equity - Shares of Common Stock Reserved for Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Common stock reserved for issuance (in shares)	45,476,994	1,099,454
Options Issued and Outstanding [Member]
Common stock reserved for issuance (in shares)	1,811,652	865,163
Options Available for Future Grants [Member]
Common stock reserved for issuance (in shares)	295,180	223,377
Common Warrants [Member]
Common stock reserved for issuance (in shares)	43,370,162	10,914