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Investments (Tables) | 9 Months Ended
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Sep. 30, 2021
Investments Debt And Equity Securities [Abstract] |
Carrying Value and Amortized Cost of Company Investments Summarized by Major Security Type | The carrying value and amortized cost of the Company’s investments, summarized by major security type, consisted of the following (in thousands):
|  | September 30, 2021 |
|  | Amortized Cost |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Estimated Fair Value |
U.S. Treasury notes |  | $ | 179,885 |  |  | $ | 4 |  |  | $ | (11 | ) |  | $ | 179,878 |
Government sponsored enterprise securities |  |  | 56,018 |  |  |  | — |  |  |  | (6 | ) |  |  | 56,012 |
Municipal bonds |  |  | 19,129 |  |  |  | — |  |  |  | (7 | ) |  |  | 19,122 |
Commercial paper |  |  | 190,631 |  |  |  | 24 |  |  |  | (16 | ) |  |  | 190,639 |
|  | $ | 445,663 |  |  | $ | 28 |  |  | $ | (40 | ) |  | $ | 445,651 |
|  | December 31, 2020 |
|  | Amortized Cost |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Estimated Fair Value |
U.S. Treasury notes |  | $ | 205,111 |  |  | $ | 6 |  |  | $ | (27 | ) |  | $ | 205,090 |
Government sponsored enterprise securities |  |  | 10,004 |  |  |  | — |  |  |  | (5 | ) |  |  | 9,999 |
Corporate debt securities |  |  | 52,341 |  |  |  | 47 |  |  |  | — |  | * |  | 52,388 |
Commercial paper |  |  | 38,443 |  |  |  | 21 |  |  |  | (11 | ) |  |  | 38,453 |
|  | $ | 305,899 |  |  | $ | 74 |  |  | $ | (43 | ) |  | $ | 305,930 |
* | Unrealized loss was less than $500.
Summary of Gross Unrealized Losses and Fair Value of Available-For-Sale Investment Securities in Unrealized Loss Position | The following table presents gross unrealized losses and fair value for those available-for-sale investment securities that were in an unrealized loss position as of September 30, 2021 and December 31, 2020, aggregated by investment category and length of time that the individual securities have been in a continuous loss position (in thousands):
|  | Less Than 12 Months |  |  | 12 Months or Greater |  |  | Total |  |
|  | Estimated Fair Value |  |  | Unrealized Losses |  |  | Estimated Fair Value |  |  | Unrealized Losses |  |  | Estimated Fair Value |  |  | Unrealized Losses |  |
September 30, 2021 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury notes |  | $ | 105,515 |  |  | $ | (11 | ) |  | $ | — |  |  | $ | — |  |  | $ | 105,515 |  |  | $ | (11 | ) |
Government sponsored enterprise securities |  |  | 56,012 |  |  |  | (6 | ) |  |  | — |  |  |  | — |  |  |  | 56,012 |  |  |  | (6 | ) |
Municipal bonds |  |  | 19,122 |  |  |  | (7 | ) |  |  | — |  |  |  | — |  |  |  | 19,122 |  |  |  | (7 | ) |
Commercial paper |  |  | 76,688 |  |  |  | (16 | ) |  |  | — |  |  |  | — |  |  |  | 76,688 |  |  |  | (16 | ) |
Total |  | $ | 257,337 |  |  | $ | (40 | ) |  | $ | — |  |  | $ | — |  |  | $ | 257,337 |  |  | $ | (40 | ) |
|  | Less Than 12 Months |  |  | 12 Months or Greater |  |  | Total |  |
|  | Estimated Fair Value |  |  | Unrealized Losses |  |  | Estimated Fair Value |  |  | Unrealized Losses |  |  | Estimated Fair Value |  |  | Unrealized Losses |  |
December 31, 2020: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury notes |  | $ | 129,631 |  |  | $ | (27 | ) |  | $ | — |  |  | $ | — |  |  | $ | 129,631 |  |  | $ | (27 | ) |
Government sponsored enterprise securities |  |  | 10,004 |  |  |  | (5 | ) |  |  | — |  |  |  | — |  |  |  | 10,004 |  |  |  | (5 | ) |
Corporate debt securities |  |  | 6,252 |  |  |  | — |  | * |  | — |  |  |  | — |  |  |  | 6,252 |  |  |  | — |  | *
Commercial paper |  |  | 23,466 |  |  |  | (11 | ) |  |  | — |  |  |  | — |  |  |  | 23,466 |  |  |  | (11 | ) |
Total |  | $ | 169,353 |  |  | $ | (43 | ) |  | $ | — |  |  | $ | — |  |  | $ | 169,353 |  |  | $ | (43 | ) |
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* | Unrealized loss was less than $500.

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