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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule of Investments [Line Items] |  |  |
Net unrealized holding losses | $ 386 | $ 836 |
Income tax benefit from unrealized holding losses during the period | 201 | 299 |
Gross realized gains from available-for-sale securities | 529 | 284 | $ 489
Gross realized losses from available-for-sale securities | 888 | 869 | 729
Investment funds sponsored by LSV | 6,034 | 4,858 |
Securities owned | 21,526 | 21,339 |
Investment funds sponsored by LSV [Member] |  |  |
Schedule of Investments [Line Items] |  |  |
Investment funds sponsored by LSV | 6,034 | 4,858 |
Change in fair value of investment funds sponsored by LSV | $ 1,176 | $ 819 | $ (389)

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