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)

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

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- Definition

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
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- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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The fair value as of the balance sheet date of firm holdings in debt obligations issued by the US government including short-term Treasury bills, medium-term Treasury notes, and long-term Treasury bonds, as well as debt issued by agencies. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

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Amount of debt and equity financial instruments classified as other and noncurrent.

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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.

+ References

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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