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Note 12 - Stock-based Compensation (Details Textual) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2023 | Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Exercises in Period | 0 | 0
Share-Based Payment Arrangement, Option [Member] |  |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount | $ 1 |
Share-Based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | 2 years 3 months 18 days |
Equity Incentive Plan 2015 [Member] |  |
Percentage of Total Shares Eligible for Plan Reserve, On an Annual Basis | 4.00% |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant | 614 |
The 2018 Employee, Director and Consultant Equity Incentive Plan [Member] |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Number of Shares Available for Grant | 0 |
The 2018 Employee, Director and Consultant Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Expiration Period | 10 years |
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period | 4 years |
The 2018 Employee, Director and Consultant Equity Incentive Plan [Member] | Share-Based Payment Arrangement, Option [Member] | Share-Based Payment Arrangement, Tranche One [Member] |  |
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Period | 1 year |
Share-Based Compensation Arrangement by Share-Based Payment Award, Award Vesting Rights, Percentage | 25.00% |

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- Definition Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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