Variable Interest Entities - Summary of Reconciliation of Carrying Value of Residential Mortgage Loans (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018
Variable Interest Entity [Line Items]
Balance at beginning of period	[1]	$ 549,016
Deductions during period:
Balance at end of period	[1]	458,348		$ 549,016
Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Balance at beginning of period		11,660
Loan acquisitions		168,850		11,660
Deductions during period:
Collections of principal		(30,992)
Balance at end of period		152,922		11,660
Variable Interest Entities Primary Beneficiary | Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Balance at beginning of period		549,016	[1]	639,351
Deductions during period:
Collections of principal		(89,113)		(88,338)
Principal paydowns and other deductions		(1,566)		(2,014)
Charge offs, net		11		17
Balance at end of period	[1]	$ 458,348		$ 549,016

[1] The consolidated balance sheets include assets of consolidated variable interest entities, or 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 December 31, 2019 and December 31, 2018, total assets of the consolidated VIEs were $460 million and $551 million (including accrued interest receivable of $1.5 million and $1.8 million), respectively (which is recorded above in the line item “Interest and dividends receivable”), and total liabilities were $450 million and $541 million (including accrued interest payable of $1.4 million and $1.7 million), respectively (which is recorded above in the line item “Accrued interest payable”). Please refer to Note 5, “Variable Interest Entities,” for further discussion.