Geographic Distribution of Mortgage Loans Held for Investment (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	100.00%	100.00%
Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	100.00%	100.00%
California
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	66.00%	68.00%
California | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	49.00%	49.00%
Washington
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	7.00%	6.00%
Washington | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	5.00%	5.00%
Texas
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	5.00%	5.00%
Texas | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	11.00%	10.00%
Illinois
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	3.00%	3.00%
Illinois | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	7.00%	6.00%
All Other
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	19.00%	18.00%
All Other | Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	28.00%	30.00%