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FAIR VALUE MEASUREMENTS - RECURRING BASIS (Details) - Recurring basis - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Fair Value on a Recurring Basis |  |
Total | $ 156,552 | $ 178,884
Money market funds |  |
Fair Value on a Recurring Basis |  |
Total | 17,915 | 7,003
Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Total | 9,995 |
Commercial paper |  |
Fair Value on a Recurring Basis |  |
Total | 35,753 | 57,587
Corporate notes |  |
Fair Value on a Recurring Basis |  |
Total | 92,516 | 113,709
Equity Investment |  |
Fair Value on a Recurring Basis |  |
Total | 373 | 585
Level 1 |  |
Fair Value on a Recurring Basis |  |
Total | 17,915 | 7,003
Level 1 | Money market funds |  |
Fair Value on a Recurring Basis |  |
Total | 17,915 | 7,003
Level 2 |  |
Fair Value on a Recurring Basis |  |
Total | 138,637 | 171,881
Level 2 | Government-sponsored enterprise securities |  |
Fair Value on a Recurring Basis |  |
Total | 9,995 |
Level 2 | Commercial paper |  |
Fair Value on a Recurring Basis |  |
Total | 35,753 | 57,587
Level 2 | Corporate notes |  |
Fair Value on a Recurring Basis |  |
Total | 92,516 | 113,709
Level 2 | Equity Investment |  |
Fair Value on a Recurring Basis |  |
Total | $ 373 | $ 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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