Residential Loans at Amortized Cost, Net - Schedule of Residential Loans at Amortized Cost, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance (1)	$ 701,944	$ 580,086
Unamortized discounts and other cost basis adjustments, net	(31,568)	(34,223)
Allowance for loan losses	(5,167)	(4,457)	$ (10,033)	$ (14,320)
Residential loans at amortized cost, net	665,209	541,406
Unencumbered Mortgage Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans at amortized cost, net	202,300	40,800
Residential Loans At Amortized Cost Net [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued Interest Receivable	$ 4,500	$ 4,600