Consolidated Securitization Vehicles and Other Variable Interest Entities - Effect on Consolidated Results (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Variable Interest Entity [Line Items]
Interest income, Assets of consolidated VIEs	$ 160,885	$ 146,900	$ 292,865	$ 297,518
Interest expense, Non-recourse liabilities of VIEs	58,772	50,426	98,022	97,179
Net interest income	137,869	149,760	276,085	332,449
Total other-than-temporary impairment losses		(2,208)		(3,260)
Portion of loss recognized in other comprehensive income		(24,893)		(31,656)
Net other-than-temporary credit impairment losses		(27,101)	(31,633)	(34,916)
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total other-than-temporary impairment losses	(612)	(1,040)	(845)	(1,437)
Portion of loss recognized in other comprehensive income	(19,462)	(20,491)	(27,326)	(27,379)
Net other-than-temporary credit impairment losses	(20,074)	(21,531)	(28,171)	(28,816)
Variable Interest Entity, Primary Beneficiary | Non-Agency Residential Mortgage-Backed Securities and Securitized Loans [Member]
Variable Interest Entity [Line Items]
Interest income, Assets of consolidated VIEs	160,885	146,900	292,865	297,518
Interest expense, Non-recourse liabilities of VIEs	58,772	50,426	98,022	97,179
Net interest income	$ 102,113	$ 96,474	$ 194,843	$ 200,339