Note 15 - Warrant Liabilities - Fair Value of Warrants (Details) $ in Thousands | Jun. 30, 2022 USD ($) yr | Mar. 31, 2022 USD ($) yr | Dec. 31, 2021 USD ($) yr | Jun. 30, 2021 USD ($) yr | Mar. 31, 2021 USD ($) yr | Feb. 18, 2021 USD ($) | Dec. 31, 2020 USD ($) yr |
Proceeds allocated to warrant liabilities | | $ 257 | $ 1,244 | | $ 6,597 | | $ 10,919 | | $ 11,921 | | $ 1,505 | |
Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | | 167 | 626 | $ 964 | 3,257 | | 5,942 | [1] | 10,476 | | | |
Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | | 22 | 84 | 132 | 431 | [1] | 817 | [1] | $ 1,445 | [1] | | |
Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | | 57 | 449 | 795 | 2,420 | | 3,370 | | | | 1,279 | |
Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | | $ 11 | $ 85 | $ 148 | 423 | | 590 | | | | 224 | |
Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | [2] | | | | 66 | | | | | | | |
Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Proceeds allocated to warrant liabilities | | | | | $ 66 | | $ 200 | [2] | | | $ 2 | [2] |
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.34 | 0.73 | 1 | 2 | | 2.64 | [1] | 4.48 | | | |
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.34 | 0.73 | 1 | 2 | [1] | 2.64 | [1] | 4.48 | [1] | | |
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.34 | 0.73 | 1 | 2 | | 2.64 | | | | 1.35 | |
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.34 | 0.73 | 1 | 2 | | 2.64 | | | | 1.35 | |
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 2 | | | | | | | |
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 2.64 | | | | 1.35 | |
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 2.13 | 2.38 | 2.63 | 3.14 | | 3.38 | [1] | 3.50 | | | |
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 2.13 | 2.38 | 2.63 | 3.14 | [1] | 3.38 | [1] | 3.50 | [1] | | |
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.45 | 1.70 | 1.95 | 2.45 | | 2.70 | | | | 2.95 | |
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.45 | 1.70 | 1.95 | 2.45 | | 2.70 | | | | 2.95 | |
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 0.05 | | | | | | | |
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 0.30 | | | | 0.05 | |
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.0297 | 0.0235 | 0.0087 | 0.0048 | | 0.0041 | [1] | 0.0026 | | | |
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.0297 | 0.0235 | 0.0087 | 0.0048 | [1] | 0.0041 | [1] | 0.0026 | [1] | | |
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.0279 | 0.0223 | 0.0072 | 0.0034 | | 0.0029 | | | | 0.0017 | |
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.0279 | 0.0223 | 0.0072 | 0.0034 | | 0.0029 | | | | 0.0017 | |
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 0.0004 | | | | | | | |
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 0.0003 | | | | 0.0008 | |
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.24 | 1.21 | 1.15 | 1.14 | | 1.68 | [1] | 1.68 | | | |
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.24 | 1.21 | 1.15 | 1.14 | [1] | 1.68 | [1] | 1.68 | [1] | | |
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.07 | 1.27 | 1.28 | 1.20 | | 1.20 | | | | 1.02 | |
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 1.07 | 1.27 | 1.28 | 1.20 | | 1.20 | | | | 1.02 | |
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 0.74 | | | | | | | |
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 2.06 | | | | 0.59 | |
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 3.59 | 3.59 | 3.59 | 3.59 | | 3.59 | [1] | 3.59 | | | |
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 4.4875 | 4.4875 | 4.4875 | 4.4875 | [1] | 4.4875 | [1] | 4.4875 | [1] | | |
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 2.03 | 2.03 | 2.03 | 2.03 | | 2.03 | | | | 2.03 | |
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 2.03 | 2.03 | 2.03 | 2.03 | | 2.03 | | | | 2.03 | |
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 1.4927 | | | | | | | |
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 1.4927 | | | | 1.4927 | |
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.064 | 0.24 | 0.37 | 1.25 | | 2.28 | [1] | 4.02 | | | |
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.061 | 0.23 | 0.36 | 1.18 | [1] | 2.24 | [1] | 3.96 | [1] | | |
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.033 | 0.26 | 0.46 | 1.40 | | 1.95 | | | | 0.74 | |
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | | 0.036 | 0.28 | 0.49 | 1.40 | | 1.95 | | | | 0.74 | |
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | 0.51 | | | | | | | |
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member] | | | | | | | | | | | | |
Fair value of the warrants | [2] | | | | | | 1.55 | | | | 0.02 | |
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[1]Closing date of the 2021 Financing.[2]The investor warrants issued in the 2018 Financing expired in July 2020. The placement agent warrants issued in the 2018 Financing were cashless exercised in July 2021. | |