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Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Investment Holdings [Line Items] |  |
Trading securities | $ 1,108,243 | $ 968,844
Senior IO Securities |  |
Investment Holdings [Line Items] |  |
Trading securities | 163,022 | 69,974
Subordinate Securities | Mezzanine |  |
Investment Holdings [Line Items] |  |
Trading securities | 602,235 | 563,475
Subordinate Securities | Subordinate |  |
Investment Holdings [Line Items] |  |
Trading securities | $ 342,986 | $ 335,395

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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