Residential Loans at Amortized Cost, Net - Summary of Residential Loans, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans, principal balance	$ 582,032		$ 1,442,838
Unamortized discounts and other cost basis adjustments, net	(35,555)		(118,266)
Allowance for loan losses	(3,585)	$ (10,660)	(10,033)	$ (11,930)	$ (12,084)	$ (14,320)
Residential loans at amortized cost, net	542,892		1,314,539
Unencumbered Forward Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans at amortized cost, net	24,400		21,800
Residential Loans At Amortized Cost Net [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest Receivable	$ 4,900		$ 12,000