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FAIR VALUE MEASUREMENTS - SECURITY TYPE (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Included in cash and cash equivalents: |  |
Amortized Cost |  | $ 10,661
Estimated Fair Value |  | 10,661
Restricted cash: |  |
Amortized Cost | $ 363 | 270
Estimated Fair Value | 363 |
Marketable securities: |  |
Amortized Cost | 228,265 | 145,200
Gross Unrealized Gains | 183 | 157
Gross Unrealized Losses | (13) | (25)
Estimated Fair Value | 228,435 | 145,332
Money market funds |  |
Included in cash and cash equivalents: |  |
Amortized Cost | 41,608 | 6,671
Estimated Fair Value | 41,608 | 6,671
Restricted cash: |  |
Amortized Cost | 92 |
Estimated Fair Value | 92 |
Commercial paper |  |
Included in cash and cash equivalents: |  |
Amortized Cost |  | 3,990
Estimated Fair Value |  | 3,990
Certificate of deposit |  |
Restricted cash: |  |
Amortized Cost | 271 | 270
Estimated Fair Value | 271 | 270
U.S. Treasury securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 5,635 |
Gross Unrealized Gains | 1 |
Estimated Fair Value | 5,636 |
Government-sponsored enterprise securities (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 3,000 | 6,506
Gross Unrealized Gains |  | 6
Estimated Fair Value | 3,000 | 6,512
Commercial paper (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 88,047 | 40,110
Gross Unrealized Gains | 49 | 33
Gross Unrealized Losses | (2) | (3)
Estimated Fair Value | 88,094 | 40,140
Corporate notes (due in less than one year) |  |
Marketable securities: |  |
Amortized Cost | 91,471 | 78,926
Gross Unrealized Gains | 107 | 116
Gross Unrealized Losses | (5) | (13)
Estimated Fair Value | 91,573 | 79,029
Corporate notes (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 29,112 | 12,659
Gross Unrealized Gains | 25 | 1
Gross Unrealized Losses | (5) | (9)
Estimated Fair Value | 29,132 | 12,651
Government-sponsored enterprise securities (due in one to two years) |  |
Marketable securities: |  |
Amortized Cost | 11,000 | 6,999
Gross Unrealized Gains | 1 | 1
Gross Unrealized Losses | (1) |
Estimated Fair Value | $ 11,000 | $ 7,000

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