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Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Schedule of Investments [Line Items]
Net unrealized gains	$ 1,879		$ 1,386
Unrealized gains during the period, income tax expense	700		430
Available-for-sale securities, gross realized gains	119	439
Available-for-sale securities, gross realized losses	49	99
Trading securities	4,914		4,849
Securities owned	21,153		21,133
Trading Securities [Member]
Schedule of Investments [Line Items]
Trading securities	$ 4,914		$ 4,849

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

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

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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.

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