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Fair Value Measurements (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Assets, Fair Value Disclosure | $ 68,264 | $ 90,749
Mutual funds |  |
Assets, Fair Value Disclosure | 33,135 | 25,967
U.S. Treasury notes |  |
Assets, Fair Value Disclosure | 23,309 | 21,094
Money market mutual fund |  |
Assets, Fair Value Disclosure | 11,820 | 43,688
Fair Value, Inputs, Level 1 [Member] |  |
Assets, Fair Value Disclosure | 68,264 | 90,749
Fair Value, Inputs, Level 1 [Member] | Mutual funds |  |
Assets, Fair Value Disclosure | 33,135 | 25,967
Fair Value, Inputs, Level 1 [Member] | U.S. Treasury notes |  |
Assets, Fair Value Disclosure | 23,309 | 21,094
Fair Value, Inputs, Level 1 [Member] | Money market mutual fund |  |
Assets, Fair Value Disclosure | 11,820 | 43,688
Fair Value, Inputs, Level 2 [Member] |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 2 [Member] | Mutual funds |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 2 [Member] | U.S. Treasury notes |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 2 [Member] | Money market mutual fund |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 3 [Member] |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Mutual funds |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 3 [Member] | U.S. Treasury notes |  |
Assets, Fair Value Disclosure | 0 | 0
Fair Value, Inputs, Level 3 [Member] | Money market mutual fund |  |
Assets, Fair Value Disclosure | $ 0 | $ 0

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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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