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Derivative Financial Instruments (Statement Of Operations Information) (Details) - Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Derivative [Line Items] |  |  |  |
Derivative financial instruments, net gain (loss) recognized | $ 1,539 | $ 1,554 | $ 5,043 | $ 5,369
Revenues - principal transactions and other income [Member] | Foreign currency forward contracts [Member] |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative financial instruments, net gain (loss) recognized | 14 | (34) | 65 | (132)
Revenues - net trading [Member] | Other Extended Settlement Trades [Member] |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative financial instruments, net gain (loss) recognized | (10) | 4 | (10) | (15)
Revenues - net trading [Member] | TBAs and Other Forward Agency MBS[Member] |  |  |  |
Derivative [Line Items] |  |  |  |
Derivative financial instruments, net gain (loss) recognized | $ 1,535 | $ 1,584 | $ 4,988 | $ 5,516

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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + 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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