Mortgage Loans - Additional Information (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Schedule Of Available For Sale Securities [Line Items]
Fair value	$ 152,197,000	$ 116,857,000
Past due on mortgage loan	0	0
Nonaccrual status on mortgage loan	0	0
Mortgage loans held for investment	1,034,000	261,000
Unpaid principal	25,676,000	16,629,000
Mortgage loans held for sale	25,919,000	17,542,000
Mortgage Loans Held for Investment in Securitization Trusts, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	204,766,000	223,205,000
Fair value	209,418,000	226,908,000
Past due on mortgage loan	0	0
Nonaccrual status on mortgage loan	0	0
Mortgage loans held for investment	1,238,000	0
Mortgage Held for Investment, at Fair Value
Schedule Of Available For Sale Securities [Line Items]
Unpaid principal balance	$ 148,691,000	$ 114,997,000