Securitized Debt - Maturities (Detail) - Variable Interest Entities, Primary Beneficiary, Aggregated Disclosure - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Securitized debt
Debt Instrument [Line Items]
Within One Year	$ 1,582,646	$ 1,608,381
One to Three Years	2,563,699	2,587,635
Three to Five Years	1,791,756	1,949,060
Greater Than Five Years	2,129,460	2,237,259
Total	8,067,561	8,382,335
Securitized Loans | Non-Agency RMBS
Debt Instrument [Line Items]
Within One Year	18,826	23,602
One to Three Years	18,332	30,803
Three to Five Years	4,453	8,047
Greater Than Five Years	665	3,605
Total	$ 42,276	$ 66,057