Note 3 - Basis of Presentation and Summary of Significant Accounting Policies - Outstanding Dilutive Securities (Details) - shares	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020
Anti-dilutive securities (in shares)	9,705,356	10,643,138
Warrant [Member]
Anti-dilutive securities (in shares)	6,499,469	9,117,209
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)	3,052,887	1,427,829
Restricted Stock [Member]
Anti-dilutive securities (in shares)	153,000	98,100

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