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Note 7 - Marketable Securities (Tables) | 3 Months Ended
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Mar. 31, 2021
Notes Tables |
Debt Securities, Available-for-sale [Table Text Block] |
|  | March 31, 2021 |
(in thousands) |  | Cost |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Fair Value |
U.S. municipal securities |  | $ | 19,281 |  |  | $ | 51 |  |  | $ | (5 | ) |  | $ | 19,327 |
Corporate debt securities |  |  | 20,010 |  |  |  | 78 |  |  |  | (30 | ) |  |  | 20,058 |
U.S. government agency securities |  |  | 3,500 |  |  |  | 1 |  |  |  | (2 | ) |  |  | 3,499 |
Certificates of deposit/time deposits |  |  | 5,395 |  |  |  | 73 |  |  |  | - |  |  |  | 5,468 |
Commercial paper |  |  | 1,000 |  |  |  | - |  |  |  | - |  |  |  | 1,000 |
Total marketable securities |  | $ | 49,186 |  |  | $ | 203 |  |  | $ | (37 | ) |  | $ | 49,352 |
Debt Securities, Held-to-maturity [Table Text Block] |
|  | December 31, 2020 |
(in thousands) |  | Cost |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Fair Value |
U.S. municipal securities |  | $ | 25,003 |  |  | $ | 83 |  |  | $ | (2 | ) |  | $ | 25,084 |
Corporate debt securities |  |  | 42,048 |  |  |  | 211 |  |  |  | (11 | ) |  |  | 42,248 |
U.S. government agency securities |  |  | 18,500 |  |  |  | 6 |  |  |  | (10 | ) |  |  | 18,496 |
Certificates of deposit/time deposits |  |  | 5,395 |  |  |  | 93 |  |  |  | - |  |  |  | 5,488 |
Commercial paper |  |  | 2,499 |  |  |  | - |  |  |  | - |  |  |  | 2,499 |
Total marketable securities |  | $ | 93,445 |  |  | $ | 393 |  |  | $ | (23 | ) |  | $ | 93,815 |
Investments Classified by Contractual Maturity Date [Table Text Block] |
|  | March 31, |
(in thousands) |  | 2021 |
Due in one year or less |  | $ | 19,592 |
Due after one year through five years |  |  | 29,760 |
Total marketable securities |  | $ | 49,352 |

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