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Real Estate Securities - Available for Sale Securities by Collateral Type (Detail) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | ---
Investment Holdings [Line Items] |  |
Available-for-sale securities | $ 829,245 | $ 1,267,624
Senior Securities |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 279,251 | 487,557
Senior Securities | Prime |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 210,993 | 307,813
Senior Securities | Non-prime |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 68,258 | 179,744
Re-REMIC |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 165,064 | 168,347
Subordinate Securities |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 384,930 | 611,720
Subordinate Securities | Prime |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 220,141 | 448,838
Subordinate Securities | Non-prime |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | 1,000 | 1,000
Subordinate Securities | Subordinate |  |
Investment Holdings [Line Items] |  |
Available-for-sale securities | $ 164,789 | $ 162,882

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