Geographic Distribution of Mortgage Loans Held for Investment (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
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	54.00%	82.00%
Texas
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	9.00%	3.00%
Illinois
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	6.00%	2.00%
Washington
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	5.00%	2.00%
All Other
Schedule Of Available For Sale Securities [Line Items]
Mortgage loans held	26.00%	11.00%