Short-Term Debt - Collateral for Short-Term Debt Facilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Short-term Debt [Line Items]
Total collateral for financing	$ 2,034,873	$ 649,106
Facilities
Short-term Debt [Line Items]
Total real estate securities owned	107,830	114,553
Other assets	1,709	315
Total collateral for financing	1,842,618	398,252
Servicer advance financing
Short-term Debt [Line Items]
Total collateral for financing	192,255	250,854
Cash	12,975	9,978
Restricted cash	19,872	23,220
Servicer advances	159,408	217,656
Held-for-sale residential loans \| Facilities
Short-term Debt [Line Items]
Market value of loans pledged as collateral under short-term borrowing agreements	1,478,424	156,355
Business purpose loans \| Facilities
Short-term Debt [Line Items]
Market value of loans pledged as collateral under short-term borrowing agreements	254,655	127,029
On balance sheet \| Facilities
Short-term Debt [Line Items]
Available-for-sale securities pledged as collateral	14,367	23,193
Sequoia \| Sequoia securities \| Short Term Borrowing Agreement \| Facilities
Short-term Debt [Line Items]
Trading securities pledged as collateral	62,075	63,105
Freddie Mac K-Series \| Sequoia securities \| Short Term Borrowing Agreement \| Facilities
Short-term Debt [Line Items]
Trading securities pledged as collateral	$ 31,388	$ 28,255

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Restricted Cash Collateral For Borrowed Securities

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Servicer Advances Collateral

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- Definition

Short-term Debt Pledged as Collateral

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Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

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Amount of restricted 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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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in net income (trading).

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Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

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The sum of the fair values, as of the date of each statement of financial position presented, of securities that are restricted as collateral for the payment of related debt obligations, primarily secured borrowings and repurchase agreements, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

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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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