Securitized Loans Held for Investment - Collateral Characteristics (Detail) (Residential Mortgage [Member], USD $)	Sep. 30, 2012 Point Loan		Dec. 31, 2011 Loan Point
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Number of loans	1,384		392
Weighted average maturity	28 years 2 months 12 days		25 years 9 months 18 days
Weighted average loan to value	71.70%	[1]	75.50%	[1]
Weighted average FICO	767	[2]	752	[2]
Weighted average loan balance	$ 820,100		$ 684,000
Weighted average percentage owner occupied	94.00%		91.10%
Weighted average percentage single family residence	65.90%		58.10%
California [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration	39.60%		36.00%
New York [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration	7.70%
Washington [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration	6.60%
Virginia [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration	4.70%
Maryland [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration	4.20%
Florida [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration			6.10%
Arizona [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration			5.80%
New Jersey [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration			5.40%
Illinois [Member]
Securitized Loans Held For Investment By Consolidated Variable Interest Entities [Line Items]
Weighted average geographic concentration			5.30%

[1] Value represents appraised value of the collateral at the time of loan origination.

[2] FICO as determined at the time of loan origination.