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Derivative Financial Instruments (Balance Sheet Information) (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Derivatives, Fair Value [Line Items] |  |
Derivative fair value | $ 574 | $ 234
Investments-trading [Member] | TBAs and Other Forward Agency MBS[Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative fair value | 5,277 | 1,063
Investments-trading [Member] | Other Extended Settlement Trades [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative fair value |  | 55
Other Investment At Fair Value [Member] | Foreign currency forward contracts [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative fair value | 3 | (26)
Trading securities sold, not yet purchased [Member] | TBAs and Other Forward Agency MBS[Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative fair value | $ (4,706) | (607)
Trading securities sold, not yet purchased [Member] | Other Extended Settlement Trades [Member] |  |
Derivatives, Fair Value [Line Items] |  |
Derivative fair value |  | $ (251)

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- Definition Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 + Details
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