Real Estate Securities - Trading Securities by Collateral Type (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Real estate securities	$ 170,619	$ 125,667
Unpaid principal balance	235,306	245,855
Principal balance of securities acquired (1)	50,180	79,921
Principal balance of securities sold (1)	55,561	744,914
Net market valuation gains (losses) recorded	23,583	(230,731)
Securities bought and sold during the same quarter	5,000	11,000
Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	21,787	28,464
Unpaid principal balance	0	0
Mezzanine
Investment Holdings [Line Items]
Real estate securities	0	3,649
Unpaid principal balance	0	3,577
Subordinate
Investment Holdings [Line Items]
Real estate securities	148,832	93,554
Unpaid principal balance	235,306	242,278
Interest-only securities \| Senior IO Securities
Investment Holdings [Line Items]
Real estate securities	21,787	28,464
Interest-only securities \| Senior IO Securities \| Sequoia
Investment Holdings [Line Items]
Real estate securities	15,000	13,000
Sequoia securities \| Mezzanine
Investment Holdings [Line Items]
Real estate securities	0	3,649
RPL securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	65,140	47,448
Multifamily securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	10,549	5,592
Other third-party residential securities \| Subordinate
Investment Holdings [Line Items]
Real estate securities	$ 73,143	$ 40,514

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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For investments which are quantified by principal amount, the principle balance held at close of period.

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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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The cash inflow associated with the sale of securities classified as trading securities and held for investment purposes. Excludes proceeds from 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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