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FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - Recurring basis - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value on a Recurring Basis |  |
Total | $ 156,382 | $ 178,884
Money market funds |  |
Fair Value on a Recurring Basis |  |
Total | 6,671 | 7,003
Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Total | 13,512 |
Commercial paper |  |
Fair Value on a Recurring Basis |  |
Total | 44,130 | 57,587
Corporate notes |  |
Fair Value on a Recurring Basis |  |
Total | 91,680 | 113,709
Equity Investment |  |
Fair Value on a Recurring Basis |  |
Total | 389 | 585
Level 1 |  |
Fair Value on a Recurring Basis |  |
Total | 6,671 | 7,003
Level 1 | Money market funds |  |
Fair Value on a Recurring Basis |  |
Total | 6,671 | 7,003
Level 2 |  |
Fair Value on a Recurring Basis |  |
Total | 149,711 | 171,881
Level 2 | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Total | 13,512 |
Level 2 | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Total | 44,130 | 57,587
Level 2 | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Total | 91,680 | 113,709
Level 2 | Equity Investment |  |
Fair Value on a Recurring Basis |  |
Total | $ 389 | $ 585

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- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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