Securitized Debt - Maturities of Long-Term Debt (Details) - Variable Interest Entities, Primary Beneficiary - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Securitized debt
Debt Instrument [Line Items]
Within One Year	$ 2,060,769	$ 1,837,055
One to Three Years	2,934,030	2,819,646
Three to Five Years	1,711,625	1,774,273
Greater Than Five Years	1,187,388	2,170,253
Total	7,893,812	8,601,227
Securitized Loans | Non-Agency RMBS
Debt Instrument [Line Items]
Within One Year	7,192	13,552
One to Three Years	2,780	11,229
Three to Five Years	1,080	1,589
Greater Than Five Years	123	305
Total	$ 11,175	$ 26,675