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Note 9 - Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2023
Notes Tables |
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] |
|  | Year ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |
Tax at federal statutory rate |  |  | 21 | % |  |  | 21 | % |  |  | 21 | %
State tax, net of federal benefit |  |  | — |  |  |  | — |  |  |  | — |
Share-based compensation |  |  | 0.2 |  |  |  | (0.5 | ) |  |  | 1.2 |
Research and development credits |  |  | 5.1 |  |  |  | 4.9 |  |  |  | 2.3 |
Section 162(m) limitation |  |  | — |  |  |  | (0.2 | ) |  |  | (0.5 | )
Other |  |  | (2.3 | ) |  |  | (1.8 | ) |  |  | (0.2 | )
Change in valuation allowance |  |  | (24.0 | ) |  |  | (23.4 | ) |  |  | (23.8 | )
Effective income tax rate |  |  | — | % |  |  | — | % |  |  | — | %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block] |
|  | December 31, |
|  | 2023 |  |  | 2022 |
Deferred tax assets: |  |  |  |  |  |  |  |
Net operating loss carryforwards |  | $ | 33,322 |  |  | $ | 28,017 |
Share-based compensation |  |  | 2,561 |  |  |  | 2,706 |
Research and development credit carryforwards |  |  | 12,557 |  |  |  | 9,681 |
Capitalized research and development expenses |  |  | 27,538 |  |  |  | 12,690 |
Other |  |  | 1,371 |  |  |  | 934 |
Total deferred tax assets |  |  | 77,349 |  |  |  | 54,028 |
Valuation allowance |  |  | (77,349 | ) |  |  | (54,002 | )
Net deferred tax assets |  |  | — |  |  |  | 26 |
Deferred tax liabilities: |  |  |  |  |  |  |  |
Operating lease right-of-use assets |  |  | — |  |  |  | (26 | )
Total deferred tax liabilities |  |  | — |  |  |  | (26 | )
Net deferred tax asset (liability) |  | $ | — |  |  | $ | — |
Summary of Income Tax Contingencies [Table Text Block] |
|  | Year ended December 31, |
|  | 2023 |  |  | 2022 |  |  | 2021 |
Beginning balance |  | $ | 6,496 |  |  | $ | 5,001 |  |  | $ | 4,500 |
Expired research and development tax credits |  | $ | (50 | ) |  | $ | — |  |  | $ | — |
Additions based on tax positions related to the current year |  |  | 1,967 |  |  |  | 1,495 |  |  |  | 501 |
Ending balance |  | $ | 8,413 |  |  | $ | 6,496 |  |  | $ | 5,001 |

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- Definition Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-2 + Details
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- Definition Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Paragraph 12 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-12 + Details
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- Definition Tabular disclosure for tax positions taken in the tax returns filed or to be filed for which it is more likely than not that the tax position will not be sustained upon examination by taxing authorities and other income tax contingencies. Includes, but is not limited to, interest and penalties, reconciliation of unrecognized tax benefits, unrecognized tax benefits that would affect the effective tax rate, tax years that remain subject to examination by tax jurisdictions, and information about positions for which it is reasonably possible that amounts unrecognized will significantly change within 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-15 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 15A -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-15A Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 19 -SubTopic 10 -Topic 740 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-19 + Details
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