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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Net unrealized losses	$ 1,873		$ 1,873		$ 779
Unrealized losses during the period, income tax benefit	559		559		233
Investments in Affiliated Funds, at fair value	5,739		5,739		6,034
Securities owned	28,981		28,981		21,526
Investment Funds Sponsored by LSV
Schedule of Investments [Line Items]
Investments in Affiliated Funds, at fair value	5,739		5,739		$ 6,034
Gains (losses) from investment funds sponsored by LSV	$ 205	$ 194	$ (295)	$ 492

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

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Accumulated unrealized gain (loss), after tax, on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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The net realized gains or losses on investments during the period, not including gains or losses on securities separately or otherwise categorized as trading, available-for-sale, or held-to-maturity.

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