Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Real estate securities	$ 125,667	$ 860,540
Unpaid principal balance	245,855	922,330
Principal balance of securities acquired	79,921	366,848
Principal balance of securities sold	744,914	592,502
Net market valuation gains (losses) recorded	(230,731)	56,046
Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	28,464	150,067
Unpaid principal balance	0	83,591
Mezzanine
Investment Holdings [Line Items]
Real estate securities	3,649	538,489
Unpaid principal balance	3,577	536,831
Subordinate
Investment Holdings [Line Items]
Real estate securities	93,554	171,984
Unpaid principal balance	242,278	301,908
Interest-only securities \| Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	28,464	64,010
Interest-only securities \| Senior IO Securities \| Sequoia Choice
Investment Holdings [Line Items]
Real estate securities	13,000	36,000
RPL securities \| Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	0	39,337
RPL securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	47,448	76,102
Other third-party residential securities \| Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	0	46,720
Other third-party residential securities \| Mezzanine
Investment Holdings [Line Items]
Real estate securities	0	103,573
Other third-party residential securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	40,514	95,882
Sequoia securities \| Mezzanine
Investment Holdings [Line Items]
Real estate securities	3,649	39,660
Multifamily securities \| Mezzanine
Investment Holdings [Line Items]
Real estate securities	0	395,256
Multifamily securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	$ 5,592	$ 0

Amount of increase (decrease) of investment in debt and equity securities, measured at fair value with changes in fair value recognized in net income.

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The cash outflow to acquire securities classified as trading securities and held for investment purposes. Excludes payments for trading securities purchased and held principally for the purpose of selling them in the near term (thus held for only a short period of time).

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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