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Marketable Securities (Narrative) (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019
Schedule of Investments [Line Items] |  |  |  |  |
Cash and cash equivalents at fair value | $ 412,663,000 |  | $ 412,663,000 |  | $ 543,765,000
Unrealized gain (loss) on investments |  |  | 0 | $ 0 |
Net unrealized gains (losses) of available-for-sale debt securities | 1,622,000 |  | 1,622,000 |  | 465,000
Unrealized gains (losses) during the period, income tax expense (benefit) | 484,000 |  | 484,000 |  | 140,000
Available-for-sale securities, gross realized gains |  |  | 0 | 0 |
Mutual funds and equities, gross realized gains |  |  | 254,000 |  |
Mutual funds and equities, gross realized loss |  |  | 250,000 |  |
Other long-term investments | 33,117,000 |  | 33,117,000 |  | 67,413,000
Securities owned | 35,820,000 |  | 35,820,000 |  | 33,486,000
Net gains or losses related to the securities | 0 | $ 0 | 0 | 0 |
Available-for-sale debt securities |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Available-for-sale securities, gross realized losses |  |  | 582,000 | 347,000 |
Investment Funds Sponsored by LSV |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Unrealized gain (loss) on investments | 458,000 | $ 99,000 | (781,000) | $ 646,000 |
Other long-term investments | $ 5,207,000 |  | $ 5,207,000 |  | $ 5,988,000

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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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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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