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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Included in cash and cash equivalents: |  |
Amortized Cost | $ 20,624 | $ 10,661
Gross Unrealized Gains | 4 |
Estimated Fair Value | 20,628 | 10,661
Restricted cash: |  |
Amortized Cost | 363 | 270
Estimated Fair Value | 363 |
Marketable securities: |  |
Amortized Cost | 241,919 | 145,200
Gross Unrealized Gains | 258 | 157
Gross Unrealized Losses | (73) | (25)
Estimated Fair Value | 242,104 | 145,332
Money market funds |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 12,629 | 6,671
Estimated Fair Value | 12,629 | 6,671
Restricted cash: |  |
Amortized Cost | 92 |
Estimated Fair Value | 92 |
Commercial paper |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 7,995 | 3,990
Gross Unrealized Gains | 4 |
Estimated Fair Value | 7,999 | 3,990
Certificate of deposit |  |
Restricted cash: |  |
Amortized Cost | 271 | 270
Estimated Fair Value | 271 | 270
Government-sponsored enterprise securities (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 3,002 | 6,506
Gross Unrealized Gains | 7 | 6
Estimated Fair Value | 3,009 | 6,512
Government-sponsored enterprise securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 6,501 | 6,999
Gross Unrealized Gains |  | 1
Gross Unrealized Losses | (1) |
Estimated Fair Value | 6,500 | 7,000
Commercial paper (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 97,225 | 40,110
Gross Unrealized Gains | 49 | 33
Gross Unrealized Losses | (31) | (3)
Estimated Fair Value | 97,243 | 40,140
Corporate notes (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 95,449 | 78,926
Gross Unrealized Gains | 198 | 116
Gross Unrealized Losses | (18) | (13)
Estimated Fair Value | 95,629 | 79,029
Corporate notes (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 39,742 | 12,659
Gross Unrealized Gains | 4 | 1
Gross Unrealized Losses | (23) | (9)
Estimated Fair Value | $ 39,723 | $ 12,651

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