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Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Assets: |  |
Total | $ 253,985 | $ 131,664
Level 1 |  |
Assets: |  |
Total | 63,229 | 3,151
Level 2 |  |
Assets: |  |
Total | 190,756 | 128,513
Money Market Funds |  |
Assets: |  |
Total | 63,229 | 3,151
Money Market Funds | Level 1 |  |
Assets: |  |
Total | 63,229 | 3,151
Commercial Paper |  |
Assets: |  |
Total | 34,901 | 4,952
Commercial Paper | Level 2 |  |
Assets: |  |
Total | 34,901 | 4,952
Corporate Debt Securities |  |
Assets: |  |
Total | 61,284 | 69,499
Corporate Debt Securities | Level 2 |  |
Assets: |  |
Total | 61,284 | 69,499
Equity Securities |  |
Assets: |  |
Total | 49,094 |
Equity Securities | Level 2 |  |
Assets: |  |
Total | 49,094 |
Asset-backed Securities |  |
Assets: |  |
Total | 16,217 | 27,055
Asset-backed Securities | Level 2 |  |
Assets: |  |
Total | 16,217 | 27,055
U.S. Government Agency Securities |  |
Assets: |  |
Total | 29,260 | 27,007
U.S. Government Agency Securities | Level 2 |  |
Assets: |  |
Total | $ 29,260 | $ 27,007

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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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