Consolidated Securitization Vehicles and Other Variable Interest Entities - Effect on Consolidated Results (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Variable Interest Entity [Line Items]
Net interest income	$ 158,183	$ 147,439
Provision for credit losses	(6,314)	0
Net other-than-temporary credit impairment losses		(4,853)
Servicing fees	9,989	8,963
Variable Interest Entities, Primary Beneficiary
Variable Interest Entity [Line Items]
Provision for credit losses	(141)	0
Net other-than-temporary credit impairment losses	0	(4,255)
Servicing fees	8,238	8,739
Variable Interest Entities, Primary Beneficiary | Non Agency Residential Mortgage Backed Securities And Securitized Loans
Variable Interest Entity [Line Items]
Interest income, Assets of consolidated VIEs	174,681	207,112
Interest expense, Non-recourse liabilities of VIEs	64,629	91,027
Net interest income	$ 110,052	$ 116,085