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Note 12 - Stock-based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2025
Notes Tables |
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] |
|  | Three Months Ended |  |  | Six Months Ended |
​ |  | June 30, |  |  | June 30, |
​ |  | 2025 |  |  | 2024 |  |  | 2025 |  |  | 2024 |
​ |  | (In thousands) |
|  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
Research and development |  | $ | 915 |  |  | $ | 1,069 |  |  | $ | 1,951 |  |  | $ | 2,083 |
Selling, general and administrative |  |  | 1,150 |  |  |  | 1,699 |  |  |  | 2,567 |  |  |  | 3,343 |
Total stock-based compensation |  | $ | 2,065 |  |  | $ | 2,768 |  |  | $ | 4,518 |  |  | $ | 5,426 |
Schedule of Share-Based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] |
​ |  | Three Months Ended |  |  | Six Months Ended |
​ |  | June 30, 2025 |  |  | June 30, 2025 |
Estimated weighted-average fair value |  | $ | 2.57 |  |  | $ | 2.61 |
Weighted-average assumptions: |  | ​ |  |  | ​ |
Expected volatility |  |  | 101 | % |  |  | 101 | %
Expected life, in years |  |  | 7.3 |  |  |  | 7.3 |
Risk-free interest rate |  |  | 4.13 | % |  |  | 4.13 | %
Expected dividend yield |  |  | — | % |  |  | — | %
Share-Based Payment Arrangement, Activity [Table Text Block] |
​ |  | ​ |  |  | Weighted- |  |  | ​ |  |  | ​ |
​ |  | ​ |  |  | Average |  |  | ​ |  |  | Aggregate |
​ |  | ​ |  |  | Exercise |  |  | Remaining |  |  | Intrinsic |
​ |  | Options |  |  | Price per |  |  | Contractual Life |  |  | Value |
​ |  | Outstanding |  |  | Share |  |  | (In years) |  |  | (In thousands) |
Balance at December 31, 2024 |  |  | 16,690,882 |  |  | $ | 8.17 |  |  |  |  |  |  |  |  |
Granted |  |  | 3,296,700 |  |  |  | 3.29 |  |  |  |  |  |  |  |  |
Exercised |  |  | (26,702 | ) |  |  | 3.30 |  |  |  |  |  |  |  |  |
Forfeited |  |  | (245,766 | ) |  |  | 14.20 |  |  |  |  |  |  |  |  |
Balance at June 30, 2025 |  |  | 19,715,114 |  |  | $ | 7.28 |  |  |  | 6.4 |  |  | $ | 558 |
Vested and expected to vest at June 30, 2025 |  |  | 18,974,796 |  |  | $ | 7.44 |  |  |  | 6.3 |  |  | $ | 534 |
Exercisable at June 30, 2025 |  |  | 12,469,143 |  |  | $ | 9.63 |  |  |  | 4.9 |  |  | $ | 288 |

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- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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- Definition Tabular disclosure of activity for award under share-based payment arrangement. Includes, but is not limited to, outstanding award at beginning and end of year, granted, exercised, forfeited, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (e) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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