Note 3 - Net Loss Per Share - Antidilutive Securities (Details) - shares	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Total potential dilutive shares (in shares)	21,906,046	20,723,459
Share-based Payment Arrangement, Option [Member]
Total potential dilutive shares (in shares)	5,977,179	4,433,392
Warrant [Member]
Total potential dilutive shares (in shares)	15,928,867	16,290,067

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration