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Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	$ 48,041		$ 48,041		$ 108,329
Unpaid principal balance	19,354		19,354		215,592
Fair value of securities acquired	0	$ 0	7,883	$ 5,006
Fair value of securities sold	27,183	4,142	82,270	27,471
Net market valuation gains (losses) recorded	5,967	$ (12,521)	14,423	$ (30,019)
Senior
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	41,169		41,169		28,867
Unpaid principal balance	0		0		0
Subordinate
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	6,872		6,872		79,462
Unpaid principal balance	19,354		19,354		215,592
Interest-only securities \| Senior
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	41,169		41,169		28,867
Interest-only securities \| Senior \| Sequoia
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	29,000		29,000		26,000
RPL securities \| Subordinate
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	0		0		29,002
Consolidated Agency multifamily loans, at fair value \| Subordinate
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	5,239		5,239		5,027
Other third-party residential securities \| Subordinate
Debt and Equity Securities, FV-NI [Line Items]
Real estate securities, at fair value	$ 1,633		$ 1,633		$ 45,433