Note 9 - Stockholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Preferred Stock, Shares Authorized (in shares)	5,000,000	5,000,000
Preferred Stock, Par or Stated Value Per Share (in dollars per share)	$ 0.0001	$ 0.0001
Preferred Stock, Shares Outstanding, Ending Balance (in shares)	0	0
Dividends, Total	$ 0
First Set of Warrants Expiring September 2024 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share)	$ 0.30
First Set of Warrants Expiring April 2024 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share)	1.10
Warrants Expiring March 2025 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share)	2.50
Warrants Expiring February 2025 [Member]
Warrant Exercise Price to be Entitled to Receive Cash Consideration, Fundamental Transaction (in dollars per share)	$ 3.125

Amount of paid and unpaid cash, stock, and paid-in-kind (PIK) dividends declared, for example, but not limited to, common and preferred stock.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-SubTopic 405
-Section 45
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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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