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Note 5 - Marketable Securities (Tables) | 3 Months Ended
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Mar. 31, 2021
Notes Tables |
Schedule of Available-for-sale Securities Reconciliation [Table Text Block] |
|  | March 31, 2021 (Unaudited) |
|  | Amortized cost |  |  | Gross unrealized gains |  |  | Gross unrealized losses |  |  | Fair value |
Available-for-sale - matures within one year: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 12,553 |  |  | $ | 61 |  |  | $ | (46 | ) |  | $ | 12,568 |
Available-for-sale - matures after one year through five years: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 71,184 |  |  |  | 497 |  |  |  | (365 | ) |  |  | 71,316 |
Total |  | $ | 83,737 |  |  | $ | 558 |  |  | $ | (411 | ) |  | $ | 83,884 |
|  | December 31, 2020 |
|  | Amortized cost |  |  | Gross unrealized gains |  |  | Gross unrealized losses |  |  | Fair value |
Available-for-sale - matures within one year: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  | $ | 12,667 |  |  | $ | 49 |  |  | $ | (7 | ) |  | $ | 12,709 |
Available-for-sale - matures after one year through five years: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Corporate bonds |  |  | 75,483 |  |  |  | 667 |  |  |  | (105 | ) |  |  | 76,045 |
Total |  | $ | 88,150 |  |  | $ | 716 |  |  | $ | (112 | ) |  | $ | 88,754 |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Table Text Block] |
|  | Less than 12 months |  |  | 12 months or greater |
|  | Fair value |  |  | Gross unrealized loss |  |  | Fair value |  |  | Gross unrealized loss |
As of March 31, 2021 (unaudited) |  | $ | 32,679 |  |  | $ | (382 | ) |  | $ | 8,372 |  |  | $ | (29 | )
As of December 31, 2020 |  | $ | 31,393 |  |  | $ | (91 | ) |  | $ | 7,381 |  |  | $ | (21 | )
Schedule of Realized Gain (Loss) [Table Text Block] |
|  | Three months ended March 31, |
|  | 2021 (unaudited) |  |  | 2020 (unaudited) |
Gross realized gains from sale of available-for-sale marketable securities |  | $ | — |  |  | $ | 4 |
Gross realized losses from sale of available-for-sale marketable securities |  | $ | — |  |  | $ | (6 | )

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- Definition Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27357-111563 + Details
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