Variable Interest Entities - Summary of Assets and Liabilities of Variable Interest Entities (Detail) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Residential mortgage loans held-for-investment	[1]	$ 667,880	$ 744,462
Accrued interest receivable		18,007	16,203
Accrued interest payable		12,690	11,850
Asset-backed securities issued by securitization trusts	[1]	658,513	728,683
Variable Interest Entities Primary Beneficiary
Variable Interest Entity [Line Items]
Accrued interest receivable		2,200	2,500
Accrued interest payable		2,200	2,400
Asset-backed securities issued by securitization trusts		658,500	728,700
Variable Interest Entities Primary Beneficiary | Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Residential mortgage loans held-for-investment		667,880	744,462
Accrued interest receivable		2,195	2,468
Total assets		670,075	746,930
Accrued interest payable		2,186	2,399
Asset-backed securities issued by securitization trusts		658,513	728,683
Total liabilities		$ 660,699	$ 731,082

[1] The consolidated balance sheets include assets of consolidated variable interest entities (“VIEs”) that can only be used to settle obligations and liabilities of the VIEs for which creditors do not have recourse to the Company. At September 30, 2017 and December 31, 2016, total assets of the consolidated VIEs were $670 million and $747 million (including accrued interest receivable of $2.2 million and $2.5 million), respectively, and total liabilities were $661 million and $731 million (including accrued interest payable of $2.2 million and $2.4 million), respectively. Please refer to Note 4, “Variable Interest Entities,” for further discussion.