Components for Mortgage Loan Held for Investment Portfolio (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) Point	Dec. 31, 2014 USD ($) Point
Schedule Of Available For Sale Securities [Line Items]
Maturity	2045-10
Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 223,205,000
Minimum
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 116,000	$ 447,000
Interest rate	2.63%	2.75%
Maturity	2044-11	2044-06
FICO score at loan origination | Point	701	705
Loan-to-value ratio at loan origination	20.00%	28.00%
Minimum | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 291,000
Interest rate	2.50%
Maturity	2044-06
FICO score at loan origination | Point	700
Loan-to-value ratio at loan origination	24.00%
Maximum
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 1,987,000	$ 1,332,000
Interest rate	4.00%	3.75%
Maturity	2046-02	2044-12
FICO score at loan origination | Point	811	813
Loan-to-value ratio at loan origination	80.00%	80.00%
Maximum | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 1,933,000
Interest rate	4.13%
Maturity	2045-11
FICO score at loan origination | Point	815
Loan-to-value ratio at loan origination	80.00%
Weighted Average
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 804,000	$ 790,000
Interest rate	3.48%	3.43%
Maturity	2045-10	2044-09
FICO score at loan origination | Point	763	762
Loan-to-value ratio at loan origination	71.00%	65.00%
Weighted Average | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 742,000
Interest rate	3.38%
Maturity	2045-03
FICO score at loan origination | Point	769
Loan-to-value ratio at loan origination	69.00%