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Note 7 - Investments (Tables) | 9 Months Ended
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Sep. 30, 2022
Notes Tables |
Marketable Securities [Table Text Block] |
|  | Amortized |  |  | Unrealized |  |  | Unrealized |  |  |  |  |
|  | Cost Basis |  |  | Gains |  |  | Losses |  |  | Fair Value |
Marketable securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
US government |  | $ | 46,554 |  |  | $ | — |  |  | $ | (102 | ) |  | $ | 46,452 |
Corporate bonds |  |  | 4,416 |  |  |  | — |  |  |  | (10 | ) |  |  | 4,406 |
Commercial paper |  |  | 12,336 |  |  |  | — |  |  |  | (24 | ) |  |  | 12,312 |
Certificates of deposit |  |  | 4,074 |  |  |  | — |  |  |  | (19 | ) |  |  | 4,055 |
Total marketable securities |  | $ | 67,380 |  |  | $ | — |  |  | $ | (155 | ) |  | $ | 67,225 |
Investments Classified by Contractual Maturity Date [Table Text Block] |
|  | September 30, |  |  | December 31, |
|  | 2022 |  |  | 2021 |
Maturities within one year |  | $ | 67,225 |  |  | $ | 44,779 |
Maturities after one year through three years |  |  | — |  |  |  | 675 |
Total investments |  | $ | 67,225 |  |  | $ | 45,454 |

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