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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands | Mar. 31, 2021 | Dec. 31, 2020
--- | --- | ---
Included in cash and cash equivalents: |  |
Amortized Cost | $ 22,999 |
Gross Unrealized Gains | 1 |
Gross Unrealized Losses | (1) |
Estimated Fair Value | 22,999 |
Restricted cash: |  |
Amortized Cost | 363 | $ 363
Estimated Fair Value | 363 | 363
Marketable securities: |  |
Amortized Cost | 212,744 | 249,659
Gross Unrealized Gains | 68 | 111
Gross Unrealized Losses | (33) | (33)
Estimated Fair Value | 212,779 | 249,737
Money market funds |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 18,000 | 4,356
Estimated Fair Value | 18,000 | 4,356
Restricted cash: |  |
Amortized Cost | 92 | 92
Estimated Fair Value | 92 | 92
Commercial paper |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 3,499 |
Gross Unrealized Losses | (1) |
Estimated Fair Value | 3,498 |
Corporate notes |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 1,500 |
Gross Unrealized Gains | 1 |
Estimated Fair Value | 1,501 |
Certificate of deposit |  |
Restricted cash: |  |
Amortized Cost | 271 | 271
Estimated Fair Value | 271 | 271
U.S. Treasury securities (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 10,653 | 5,608
Gross Unrealized Gains | 7 | 2
Estimated Fair Value | 10,660 | 5,610
U.S. Treasury securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 5,072 | 5,093
Gross Unrealized Gains | 1 | 2
Estimated Fair Value | 5,073 | 5,095
Government-sponsored enterprise securities (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 22,248 | 5,249
Gross Unrealized Gains | 8 | 3
Estimated Fair Value | 22,256 | 5,252
Government-sponsored enterprise securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 6,500 | 23,499
Gross Unrealized Gains |  | 7
Gross Unrealized Losses | (1) | (1)
Estimated Fair Value | 6,499 | 23,505
Commercial paper (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 76,944 | 112,388
Gross Unrealized Gains | 18 | 29
Gross Unrealized Losses | (1) | (8)
Estimated Fair Value | 76,961 | 112,409
Corporate notes (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 69,596 | 63,051
Gross Unrealized Gains | 28 | 35
Gross Unrealized Losses | (11) | (7)
Estimated Fair Value | 69,613 | 63,079
Corporate notes (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 21,731 | 34,771
Gross Unrealized Gains | 6 | 33
Gross Unrealized Losses | (20) | (17)
Estimated Fair Value | $ 21,717 | $ 34,787

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