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Marketable Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Net unrealized losses	$ 2,016		$ 779
Unrealized losses during the period, income tax benefit	642		233
Fair value of investment funds sponsored by LSV	5,534		6,034
Securities owned	21,600		21,526
Investment Funds Sponsored by LSV [Member]
Schedule of Investments [Line Items]
Fair value of investment funds sponsored by LSV	5,534		$ 6,034
Gains (losses) from investment funds sponsored by LSV	$ (500)	$ 298

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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.

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