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Cash Equivalents and Marketable Securities | 9 Months Ended
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Sep. 30, 2021
Cash Equivalents And Marketable Securities [Abstract] |
Cash Equivalents and Marketable Securities | 4. Cash Equivalents and Marketable Securities We invest in certain U.S. government money market funds classified as cash equivalents. The marketable securities consist of high investment grade fixed income securities that are primarily invested in commercial paper, corporate bonds, and U.S. government securities. Cash equivalents and marketable securities classified as available-for-sale consisted of the following:
|  | September 30, 2021 |
|  | Amortized Cost Basis |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Estimated Fair Value |
|  | (in thousands) |
Cash equivalents: |  |  |  |  |  |  |  |  |  |  |  |
Money market funds |  | $ | 69,644 |  |  | $ | — |  |  | $ | — |  |  | $ | 69,644 |
Short-term marketable securities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. treasury notes |  |  | 60,526 |  |  |  | 29 |  |  |  | — |  |  |  | 60,555 |
Commercial paper |  |  | 184,273 |  |  |  | 7 |  |  |  | (3 | ) |  |  | 184,277 |
Corporate debt securities |  |  | 134,365 |  |  |  | 10 |  |  |  | (24 | ) |  |  | 134,351 |
Supranational debt securities |  |  | 40,081 |  |  |  | 1 |  |  |  | (1 | ) |  |  | 40,081 |
Total short-term marketable securities |  |  | 419,245 |  |  |  | 47 |  |  |  | (28 | ) |  |  | 419,264 |
Total cash equivalents and marketable securities |  | $ | 488,889 |  |  | $ | 47 |  |  | $ | (28 | ) |  | $ | 488,908 |
|  | December 31, 2020 |
|  | Amortized Cost Basis |  |  | Unrealized Gains |  |  | Unrealized Losses |  |  | Estimated Fair Value |
|  | (in thousands) |
Cash equivalents: |  |  |  |  |  |  |  |  |  |  |  |
Money market funds |  | $ | 266,437 |  |  | $ | — |  |  | $ | — |  |  | $ | 266,437 |
Short-term marketable securities: |  |  |  |  |  |  |  |  |  |  |  |
U.S. treasury bills |  |  | 14,996 |  |  |  | 3 |  |  |  | — |  |  |  | 14,999 |
U.S. treasury notes |  |  | 45,292 |  |  |  | 100 |  |  |  | (1 | ) |  |  | 45,391 |
Commercial paper |  |  | 144,851 |  |  |  | — |  |  |  | — |  |  |  | 144,851 |
Corporate debt securities |  |  | 45,680 |  |  |  | 93 |  |  |  | (3 | ) |  |  | 45,770 |
Total short-term marketable securities |  |  | 250,819 |  |  |  | 196 |  |  |  | (4 | ) |  |  | 251,011 |
Total cash equivalents and marketable securities |  | $ | 517,256 |  |  | $ | 196 |  |  | $ | (4 | ) |  | $ | 517,448 |
There have been no significant realized gains or losses on available-for-sale securities for the periods presented. There were no available-for-sale securities that have been in a continuous unrealized loss position for more than 12 months. As of September 30, 2021, our short-term marketable securities have average contractual maturities of approximately seven months. We believe that we have the ability to realize the full value of all of these investments upon their respective maturities.

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- Definition Cash equivalents and marketable securities. + References No definition available. + Details
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- Definition The entire disclosure of cash, cash equivalents, and debt and equity securities, including any unrealized or realized gain (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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