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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Schedule of Investments [Line Items] |  |  |
Cash equivalents fair value | $ 462,624 | $ 543,765 |
Net unrealized holding gain (loss) | 1,551 | (465) |
Net unrealized holding gains (losses), income tax expense (benefit) | 464 | (140) |
Equity securities, gross realized gains | 1,100 | 297 |
Equity securities, gross realized losses | 250 | 48 |
Investment funds sponsored by LSV | 98,433 | 67,413 |
Securities owned | 34,064 | 33,486 |
Available for sale debt securities |  |  |
Schedule of Investments [Line Items] |  |  |
Available-for-sale securities, gross realized losses | 902 | 493 |
Available-for-sale securities, gross realized gains | 0 | 0 |
Investment funds sponsored by LSV |  |  |
Schedule of Investments [Line Items] |  |  |
Investment funds sponsored by LSV | 6,166 | 5,988 |
Gains (losses) from the change in fair value of the funds | $ 178 | $ 1,101 | $ (1,147)

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- Definition Amount, after tax, of accumulated unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e681-108580 + Details
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