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Marketable Securities (Tables) | 12 Months Ended
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Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |
Schedule for Available-for-Sale Securities | The following is a summary of available-for-sale securities as of December 31, 2020 (in thousands):
| Amortized Cost |  | Gross Unrealized Gain |  | Gross Unrealized (Losses) |  | Estimated Fair Value
Corporate debt securities | $ | 17,086 |  |  | $ | 452 |  |  | $ | — |  |  | $ | 17,538 |
Tax-exempt municipal securities | 19,924 |  |  | 365 |  |  | — |  |  | 20,289 |
Total | $ | 37,010 |  |  | $ | 817 |  |  | $ | — |  |  | $ | 37,827 |
The following is a summary of available-for-sale securities as of December 31, 2019 (in thousands):
| Amortized Cost |  | Gross Unrealized Gain |  | Gross Unrealized (Losses) |  | Estimated Fair Value
Corporate debt securities | $ | 42,584 |  |  | $ | 165 |  |  | $ | (40) |  |  | $ | 42,709 |
Tax-exempt municipal securities | 23,301 |  |  | 112 |  |  | (215) |  |  | 23,198 |
Variable rate demand notes | 5,600 |  |  | — |  |  | — |  |  | 5,600 |
Total | $ | 71,485 |  |  | $ | 277 |  |  | $ | (255) |  |  | $ | 71,507 |
Schedule of Maturities of Marketable Securities | The following table summarizes the maturities of the Company’s marketable securities as of December 31, 2019 and 2020 (in thousands):
| December 31, 2019 |  | December 31, 2020
Due within one year | $ | 34,874 |  |  | $ | 7,557 |
Due after one year through five years | 36,633 |  |  | 30,270 |
Total | $ | 71,507 |  |  | $ | 37,827 |
Schedule of Proceeds from the Maturities of Available-for-Sale Securities | The following table summarizes the proceeds from the maturities and sales of available-for-sale securities for the years ended December 31, 2018, 2019, and 2020 (in thousands):
| December 31, 2018 |  | December 31, 2019 |  | December 31, 2020
Maturities of marketable securities | $ | 16,367 |  |  | $ | 43,762 |  |  | $ | 34,728 |
Sales of marketable securities | — |  |  | — |  |  | 1,464 |
Total | $ | 16,367 |  |  | $ | 43,762 |  |  | $ | 36,192 |

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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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