Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investment Holdings [Line Items]
Trading securities	$ 445,687	$ 404,011
Senior Securities
Investment Holdings [Line Items]
Trading securities	37,067	254,351
Senior Securities | Prime
Investment Holdings [Line Items]
Trading securities	32,230	248,570
Senior Securities | Non-prime
Investment Holdings [Line Items]
Trading securities	4,837	5,781
Subordinate Securities
Investment Holdings [Line Items]
Trading securities	408,620	149,660
Subordinate Securities | Prime mezzanine
Investment Holdings [Line Items]
Trading securities	243,451	136,140
Subordinate Securities | Prime subordinate
Investment Holdings [Line Items]
Trading securities	$ 165,169	$ 13,520