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Financial Instruments (Schedule Of Trading Securities Sold, Not Yet Purchased) (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
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Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | $ 81,220 | $ 91,887
U.S. government agency MBS and CMOs [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | 17 |
U.S. Treasury securities [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | 42,015 | 62,798
Corporate bonds and redeemable preferred stock [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | 34,462 | 28,445
Municipal bonds [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | 20 | 37
Derivatives [Member] |  |
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items] |  |
Trading securities sold, not yet purchased | $ 4,706 | $ 607

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- Definition Fair value of obligations incurred from short sales. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 35 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35711043&loc=d3e42429-110968 + Details
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- Definition 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. + References No definition available. + Details
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