Residential Loans - Characteristics of Residential Loans Held-for-Sale (Details) - Residential Loans $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021 USD ($) loan	Dec. 31, 2020 USD ($) loan
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans \| loan	1,115	198
Unpaid principal balance	$ 990,841	$ 172,748
Fair value of loans	996,512	176,641
Market value of loans pledged as collateral under short-term borrowing agreements	$ 926,076	$ 156,355
Number of loans in foreclosure \| loan	0	0
Financing Receivables, Equal to Greater than 90 Days Past Due
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Number of loans with 90+ day delinquencies \| loan	1	1
Unpaid principal balance of loans with 90+ day delinquencies	$ 1,882	$ 1,882
Fair value of loans with 90+ day delinquencies	$ 1,223	$ 1,223

Financing Receivable, Number Of Loans In Foreclosure

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Financing Receivable, Number Of Loans Past Due

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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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Number of mortgage loans within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Footnote 3
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This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

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Amount of financing receivable past due.

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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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Amount, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement.

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This is the sum of principal amount outstanding for both securitized and unsecuritized loans of all types.

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