Variable Interest Entities - Carrying Value for Residential Mortgage Loans (Detail) - USD ($) $ in Thousands		Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity [Line Items]
Carrying value	[1]	$ 367,539		$ 458,348
Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Principal balance		127,782		148,908
Unamortized premium and costs		3,384		4,014
Allowance for loan losses		(56)	$ (56)
Carrying value		131,110	141,645	152,922			$ 11,660
Variable Interest Entities Primary Beneficiary
Variable Interest Entity [Line Items]
Allowance for loan losses				(175,000)
Variable Interest Entities Primary Beneficiary | Residential Mortgage Backed Securities
Variable Interest Entity [Line Items]
Principal balance		366,584		456,768
Unamortized premium and costs		1,102		1,755
Allowance for loan losses		(147)	(167)	(175)	$ (175)			$ (175)	$ (186)
Carrying value		$ 367,539	$ 416,571	$ 458,348	$ 514,749	$ 535,077	$ 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 June 30, 2020 and December 31, 2019, total assets of the consolidated VIEs were $369 million and $460 million (including accrued interest receivable of $1.3 million and $1.5 million), respectively (which is recorded above in the line item entitled “Interest receivable”), and total liabilities were $360 million and $450 million (including accrued interest payable of $1.2 million and $1.4 million), respectively (which is recorded in the line item above entitled “Accrued interest payable”). Please refer to Note 5, “Variable Interest Entities,” for further discussion.