Note 10 - Equity, Share-based Compensation, Warrants and Securities Offerings (Details Textual) - USD ($) $ / shares in Units, $ in Millions | Sep. 13, 2021 | Feb. 28, 2022 | Mar. 17, 2022 | Sep. 30, 2021 | Dec. 31, 2021 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Jun. 30, 2020 | Jun. 30, 2018 |
Common Stock, Shares Authorized (in shares) | | | | | | 150,000,000 | | 150,000,000 | | 150,000,000 | | | 50,000,000 | |
Proceeds from Issuance or Sale of Equity, Total | | | | | | $ 3.6 | | | | | | | | |
Common Stock, Capital Shares Reserved for Future Issuance (in shares) | | | | | | 5,813,021 | | 5,813,021 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares) | | | | | | 8,750,673 | [1] | 8,750,673 | [1] | 6,645,916 | [1] | 7,532,280 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | 1 year 8 months 12 days | | | | | | |
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount | | | | | | $ 0.2 | | $ 0.2 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, NonOption Equity Instruments, Weighted Average Exercise Price (in dollars per share) | | | | | | $ 0.96 | | $ 0.96 | | $ 0.96 | [2] | | | |
Share-based Payment Arrangement, Option [Member] | Minimum [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award Options Exercisable Period (Year) | | | | | | | | | | 3 years | | | | |
Share-based Payment Arrangement, Option [Member] | Maximum [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award Options Exercisable Period (Year) | | | | | | | | | | 4 years | | | | |
Restricted Stock Units (RSUs) [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares) | | | | | | 1,409,303 | | 1,409,303 | | 386,403 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | | | | | | | | $ 0.55 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | | | 2 years | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non Option Equity Instruments Impact of Warrant Modification, Prior To Modification (in shares) | [3] | | | | | | | 0 | | 227,062 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | | | | | | 1,266,033 | | 1,266,033 | | 1,495,400 | | 1,148,062 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Impact Of Warrant Modification After Modification (in shares) | [4] | | | | | | | 0 | | 620,000 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Nonoption, Equity Instruments Impact Of Warrant Modification After Modification Vesting, Percentage | | | | | | | | | | 50.00% | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares) | [5] | | | | | | | 1,051,149 | | 386,403 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | [6] | | | | | | | 824,689 | | 1,261,803 | | | | |
Restricted Stock Units (RSUs) [Member] | Subsequent Event [Member] | Share-based Payment Arrangement, Employee [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share) | | | | $ 0.91 | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | 224,751 | | | | | | | | | | |
Restricted Stock Units (RSUs) [Member] | Share-based Payment Arrangement, Tranche Two [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | | | | | | | | | | | | 5 years | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year) | | | | | | | | 2 years | | 2 years | | | | |
Number of Trading Days (Day) | | | | | | | | | | 65 days | | 65 days | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award VestingP rice (in dollars per share) | | | | | | | | | | $ 10 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | | | | | | | | | | 68,119 | | | | |
Restricted Stock Units (RSUs) [Member] | Share-based Payment Arrangement, Tranche One [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non Option Equity Instruments Impact of Warrant Modification, Prior To Modification (in shares) | | | | | | | | | | 22,706 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award VestingP rice (in dollars per share) | | | | | | | | | | $ 5 | | | | |
Restricted Stock Units (RSUs) [Member] | Share-based Payment Arrangement, Tranche Three [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award VestingP rice (in dollars per share) | | | | | | | | | | $ 15 | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | | | | | | | | | | 136,237 | | | | |
Deferred Restricted Stock Units (RSUs) [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number, Ending Balance (in shares) | | | | | | 1,209,092 | | 1,209,092 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period (in shares) | | | | | | | | 865,052 | | | | | | |
Warrants [Member] | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | | | | | 8,750,673 | | 8,750,673 | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | | | | | | $ 1 | | $ 1 | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares) | | | | | | 3,484,675 | | 3,484,675 | | | | | | |
Stock Issued During Period, Cashless Exercise Of Warrants Shares (in shares) | | | | | | | | 2,307,498 | | 54,629 | | | | |
The 2014 Equity Incentive Plan [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized (in shares) | | | | | | | | | | | | | | 6,300,000 |
Common Stock, Capital Shares Reserved for Future Issuance (in shares) | | | | | | 486,979 | | 486,979 | | | | | | |
The 2014 Equity Incentive Plan [Member] | Share-based Payment Arrangement, Option [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year) | | | | | | | | 10 years | | | | | | |
The 2014 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number, Ending Balance (in shares) | | | | | | 1,000,000 | | 1,000,000 | | | | | | |
The 2014 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Subsequent Event [Member] | Share-based Payment Arrangement, Employee [Member] | | | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | | 370,000 | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Accelerated Vesting, Number (in shares) | | | | 2 | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares) | | | | 1,898,781 | | | | | | | | | | |
The Warrant [Member] | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | 2,307,693 | | | | 2,307,696 | | 2,307,696 | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | | $ 1 | | | | $ 1 | | $ 1 | | | | | | |
Class of Warrant or Right, Change in Exercise Price, Maximum Percentage of Five-day Volume Weighted Average Common Stock | | 110.00% | | | | | | 110.00% | | | | | | |
Warrants and Rights Outstanding | | $ 0.6 | | | | | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, NonOption Equity Instruments, Weighted Average Exercise Price (in dollars per share) | | | | | | $ 0.96 | | $ 0.96 | | | | | | |
Class of Warrant or Right, Warrants Expired During Period (in shares) | | | 6,142,980 | | | | | | | | | | | |
Class of Warrant or Right, Expired, Exercise Price (in dollars per share) | | | $ 0.96 | | | | | | | | | | | |
Prefunded Warrant [Member] | | | | | | | | | | | | | | |
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares) | | 2,307,855 | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share) | | $ 0.0001 | | | | | | | | | | | | |
Class of Warrant or Right, Exercise Price, Prefunded (in dollars per share) | | $ 0.6499 | | | | | | | | | | | | |
Offering Pursuant to Shelf Registration Statement [Member] | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | 2,307,500 | | | | | | | | | | | | |
Proceeds from Issuance or Sale of Equity, Total | | $ 2.8 | | | | | | | | | | | | |
Payments of Stock Issuance Costs | | $ 0.2 | | | | | | | | | | | | |
At-the-market Offering Program [Member] | | | | | | | | | | | | | | |
Stock Issued During Period, Shares, New Issues (in shares) | | | | | 754,895 | | | | | 4,850,489 | | | | |
Proceeds from Issuance or Sale of Equity, Total | | | | | | $ 0.6 | | | | | | | | |
Payments of Stock Issuance Costs | | | | | $ 0.1 | | | | | $ 0.2 | | | | |
Shares Issued, Price Per Share (in dollars per share) | | | | | $ 0.80 | | | | | $ 0.53 | | | | |
Proceeds from Issuance of Common Stock | | | | | $ 0.5 | | | | | | | | | |
Series A Through F Preferred Stock [Member] | | | | | | | | | | | | | | |
Preferred Stock, Shares Outstanding, Ending Balance (in shares) | | | | | | 0 | | 0 | | | | | | |
Series G Preferred Stock [Member] | | | | | | | | | | | | | | |
Preferred Stock, Shares Outstanding, Ending Balance (in shares) | | | | | | 150 | | 150 | | 225 | | | | |
Convertible Preferred Stock, Shares Issued upon Conversion (in shares) | | | | | | 948.9915 | | 948.9915 | | | | | | |
Preferred Stock, Liquidation Preference Per Share (in dollars per share) | | | | | | $ 1,000 | | $ 1,000 | | | | | | |
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[1] | Under the terms of certain outstanding warrants, the holders may elect to exercise the warrants under a cashless exercise feature. As of December 31, 2021, warrant holders may elect to exercise cashless warrants for 3,484,675 shares of common stock at an exercise price of $0.96 per share and 2,307,696 shares of common stock at an exercise price of $1.00 per share. If we register for resale the shares subject to warrants, the holders of some of the warrants may no longer have the right to elect a cashless exercise. If we fail to maintain a registration statement for the resale of shares under certain other warrants, the shares under those warrants may again become exercisable using a cashless exercise feature. | |
[2] | We issued 54,629 shares of common stock upon the cashless exercise of the warrants in 2020. | |
[3] | In December 2020, we modified RSUs for a total of 227,062 shares of common stock. Prior to modification, the shares subject to the RSUs vested based upon a vesting price equal to the volume weighted average trading price of our common stock over sixty-five consecutive trading days. Subject to a minimum service period, as described in the next sentence, the RSU shares vested as to (i) 22,706 shares on the date the vesting price equals or exceeds $5.00 per share, (ii) 68,119 shares on the date the vesting price equals or exceeds $10.00 per share and (iii) 136,237 shares on the date the vesting price equals or exceeds $15.00 per share. Vesting on the RSU shares would have occurred the later of the one-year anniversary of the grant and the date the shares reach the vesting price indicated in the preceding sentence. The RSUs expire on the fifth anniversary of each grant at dates ranging from October 2023 to August 2024. | |
[4] | In December 2020, after modification, shares subject to the modified RSUs referred to above totaled 620,000 and vest as to 50% of the shares in December 2021 and as to the remainder of the shares in December 2022. We are recognizing the total of (i) the remaining unrecognized compensation on the awards as of the modification date and (ii) the increase in fair value of the RSUs as a result of the modification, over the remaining two-year vesting period of the RSUs. | |
[5] | Represents the following. 2021 2020 Vested when granted 386,403 386,403 Vested upon completion of service conditions, common stock issued at vesting 572,500 - Vested upon completion of service, common stock issuance deferred 450,400 - Outstanding at December 31 1,409,303 386,403 | |
[6] | The shares of common stock subject to the RSUs granted in 2021 and 2020, were vested when granted or vest within two years of grant. These RSU grants were not subject to any market conditions and were valued using the market price of our common stock on the date of grant. Prior to being modified in 2020, the shares of common stock subject to the RSUs granted in 2019 vested based upon a vesting price equal to the volume weighted average trading price of our common stock over sixty-five consecutive trading days, subject to a minimum service period in certain grants, and expired on the fifth anniversary of each grant. | |