Real Estate Securities - Trading Securities by Collateral Type (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Trading securities	$ 116,141	$ 111,606
Senior Securities
Investment Holdings [Line Items]
Trading securities	69,132	101,753
Senior Securities | Prime
Investment Holdings [Line Items]
Trading securities	62,427	93,802
Senior Securities | Non-prime
Investment Holdings [Line Items]
Trading securities	6,705	7,951
Subordinate Securities | Prime
Investment Holdings [Line Items]
Trading securities	$ 47,009	$ 9,853