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Note 3 - Income Taxes (Details Textual) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2018
Deferred Tax Assets, Capitalized Research and Development | $ 2,233 | $ 1,053 |
Stock Issued During Period, Value, Stock Options Exercised | 0 | 42 |
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued | 0 | 0 |
Unrecognized Tax Benefits that Would Impact Effective Tax Rate | 470 | 326 |
Fuel Tech S.p.A [Member] |  |  |
Deferred Federal Income Tax Expense (Benefit), Net of Adjustment | 136 | $ 149 |
Increase (Decrease) in Deferred Income Taxes | (13) |  |
Deferred Income Tax Expense, Valuation Allowance | (136) |  |
Domestic Tax Jurisdiction [Member] |  |  |
Operating Loss Carryforwards | 27,054 |  | $ 8,378
Foreign Tax Jurisdiction [Member] | Ministry of Economic Affairs and Finance, Italy [Member] |  |  |
Operating Loss Carryforwards | 6,459,000 |  |
Foreign Tax Jurisdiction [Member] | State Administration of Taxation, China [Member] |  |  |
Operating Loss Carryforwards | $ 1,098,000 |  |

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