Real Estate Securities - Trading Securities by Collateral Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Investment Holdings [Line Items]
Trading securities	$ 404,011	$ 111,606
Senior Securities
Investment Holdings [Line Items]
Trading securities	254,351	101,753
Senior Securities | Prime
Investment Holdings [Line Items]
Trading securities	248,570	93,802
Senior Securities | Non-prime
Investment Holdings [Line Items]
Trading securities	5,781	7,951
Subordinate Securities | Prime
Investment Holdings [Line Items]
Trading securities	149,660	9,853
Subordinate Securities | Real Estate Securities, Prime Mezzanine [Member]
Investment Holdings [Line Items]
Trading securities	136,140	0
Subordinate Securities | Real Estate Securities, Prime Subordinate [Member]
Investment Holdings [Line Items]
Trading securities	$ 13,520	$ 9,853