Consolidated Securitization Vehicles and Other Variable Interest Entities - Effect on Consolidated Results (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Variable Interest Entity [Line Items]
Net interest income	$ 156,042	$ 143,966	$ 432,126	$ 476,415
Total other-than-temporary impairment losses	(993)	(3,129)	(8,555)	(6,389)
Portion of loss recognized in other comprehensive income	(10,581)	(14,703)	(34,652)	(46,359)
Net other-than-temporary credit impairment losses	(11,574)	(17,832)	(43,207)	(52,748)
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Total other-than-temporary impairment losses	(21)	(301)	(866)	(1,738)
Portion of loss recognized in other comprehensive income	(4,599)	(15,838)	(31,925)	(43,217)
Net other-than-temporary credit impairment losses	(4,620)	(16,139)	(32,791)	(44,955)
Variable Interest Entity, Primary Beneficiary | Non Agency Residential Mortgage Backed Securities And Securitized Loans
Variable Interest Entity [Line Items]
Interest income, Assets of consolidated VIEs	195,488	142,053	488,353	439,571
Interest expense, Non-recourse liabilities of VIEs	70,715	50,837	168,738	148,017
Net interest income	$ 124,773	$ 91,216	$ 319,615	$ 291,554