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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 | Dec. 31, 2018
Schedule of Investments [Line Items] |  |  |  |  |
Net unrealized gains (losses) of available-for-sale debt securities | $ 327 |  | $ 327 |  | $ (1,413)
Unrealized gains (losses) during the period, income tax expense (benefit) | 97 |  | 97 |  | (422)
Available-for-sale securities, gross realized gains |  |  |  | $ 1,004 |
Available-for-sale securities, gross realized losses |  |  |  | 1,310 |
Investments in Affiliated Funds, at fair value | 5,434 |  | 5,434 |  | 4,887
Securities owned | 32,289 |  | 32,289 |  | 30,892
Investment Funds Sponsored by LSV |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Investments in Affiliated Funds, at fair value | 5,434 |  | 5,434 |  | $ 4,887
Gains (losses) from investment funds sponsored by LSV | $ 95 | $ 205 | $ 547 | $ (295) |

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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=118930883&loc=d3e681-108580 + Details
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- Definition Amount of realized gain 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/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563 + Details
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- Definition Amount of realized 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/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27357-111563 + Details
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