Variable Interest Entities - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
		Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Variable Interest Entity [Line Items]
Gain on sales of residential mortgage loans held-for-investment		$ 716	$ 378	$ 749
Asset-backed securities issued by securitization trusts	[1]		658,513		$ 728,683
Variable Interest Entities Primary Beneficiary
Variable Interest Entity [Line Items]
Asset-backed securities issued by securitization trusts			$ 658,500		$ 728,700

[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.