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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Investments [Line Items] |  |  |
Net unrealized holding losses | $ 1,413 | $ 779 |
Net unrealized holding losses, income tax benefit | 422 | 233 |
Gross realized gains from available-for-sale securities | 1,065 | 529 | $ 284
Gross realized losses from available-for-sale securities | 1,686 | 888 | 869
Investment funds sponsored by LSV | 4,887 | 6,034 |
Securities owned | 30,892 | 21,526 |
Investment funds sponsored by LSV |  |  |
Schedule of Investments [Line Items] |  |  |
Investment funds sponsored by LSV | 4,887 | 6,034 |
Change in fair value of investment funds sponsored by LSV | $ (1,147) | $ 1,176 | $ 819

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