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Note 9 - Stock-Based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions |  | 12 Months Ended |
--- | --- | --- | ---
Apr. 29, 2019 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2016
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) |  | 4,694,000 | 3,763,000 |  |
Share Price (in dollars per share) |  | $ 3.96 | $ 12.30 |  |
Stock or Unit Option Plan Expense |  | $ 6.4 | $ 3.9 |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total |  | $ 10.7 |  |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year) |  | 2 years 1 month 6 days |  |  |
The 2019 Stock Plan [Member] |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period (Year) | 10 years |  |  | 10 years |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) | 200,000 |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Grants in Period, Net of Forfeitures, Total (in shares) |  | 1.3 | 1,140,000 |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) |  | 4,694,000 | 3,763,000 | 5,327,000 |
Share Price (in dollars per share) |  | $ 10.97 | $ 5.60 |  |
The 2019 Stock Plan [Member] | Maximum [Member] |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period (Year) |  |  |  | 3 years |
The 2019 Stock Plan [Member] | Restricted Stock [Member] |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) |  | 89,000 | 154,000 |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value, Ending Balance (in dollars per share) |  | $ 10.92 |  |  |
Amended and Restated 2007 Stock Plan [Member] |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) | 177,246 |  |  |  |
Inducement Equity Plan Options [Member] |  |  |  |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Authorized (in shares) |  |  |  |  | 100,000
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) |  | 0 |  |  |

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