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Short-term Investments | 12 Months Ended
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Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract] |
Short-term Investments | Short-term Investments The Company's investments are classified as available-for-sale. The following table summarizes the amortized cost, gross unrealized gains and losses, and fair value of available-for-sale investments as of December 31, 2020:
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Aggregate Fair Value
United States government debt securities | $ | 48,048 |  |  | $ | 14 |  |  | $ | (1) |  |  | $ | 48,061 |
Certificates of deposit | 264 |  |  | — |  |  | — |  |  | 264 |
Total | $ | 48,312 |  |  | $ | 14 |  |  | $ | (1) |  |  | $ | 48,325 |
The following table summarizes the amortized cost, gross unrealized gains and losses, and fair value of available-for-sale investments as of December 31, 2019:
| Amortized Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Aggregate Fair Value
United States government debt securities | $ | 8,989 |  |  | $ | 7 |  |  | $ | — |  |  | $ | 8,996 |
Certificates of deposit | 264 |  |  | — |  |  | — |  |  | 264 |
Total | $ | 9,253 |  |  | $ | 7 |  |  | $ | — |  |  | $ | 9,260 |
See Notes 2 and 8 for further discussion on the Company's method for determining the fair value of its assets. As of December 31, 2020, all of the available-for-sale investments were due within one year based on their contractual maturities. Changes in market interest rates and bond yields cause certain investments to fall below their cost basis, resulting in unrealized losses on investments. The unrealized losses of the Company's investments were primarily a result of unfavorable changes in interest rates subsequent to the initial purchase of these investments and are not significant as of December 31, 2020.

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