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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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Accumulated Other Comprehensive Income (Loss), Debt Securities, Available For Sale Securities Adjustment Tax

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