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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

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