Real Estate Securities - Available for Sale Securities by Collateral Type (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Debt securities, available for sale	$ 218,458	$ 239,334
AFS securities acquired	57,652	26,538
AFS securities sold	55,192	110,070
Gross realized gains	4,635	17,582
Senior IO Securities
Investment Holdings [Line Items]
Debt securities, available for sale	0	25,792
Mezzanine
Investment Holdings [Line Items]
Debt securities, available for sale	2,014	13,687
Subordinate
Investment Holdings [Line Items]
Debt securities, available for sale	216,444	199,855
Other third-party residential securities \| Senior IO Securities
Investment Holdings [Line Items]
Debt securities, available for sale	0	25,792
Other third-party residential securities \| Mezzanine
Investment Holdings [Line Items]
Debt securities, available for sale	2,014	4,244
Other third-party residential securities \| Subordinate
Investment Holdings [Line Items]
Debt securities, available for sale	36,306	59,776
Sequoia securities \| Mezzanine
Investment Holdings [Line Items]
Debt securities, available for sale	0	4,320
Sequoia securities \| Subordinate
Investment Holdings [Line Items]
Debt securities, available for sale	136,475	136,330
Multifamily securities \| Mezzanine
Investment Holdings [Line Items]
Debt securities, available for sale	0	5,123
Multifamily securities \| Subordinate
Investment Holdings [Line Items]
Debt securities, available for sale	$ 43,663	$ 3,749

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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