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Securities, at Fair Value - Narrative (Details) - USD ($) |  | 3 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2021 | Jun. 30, 2021 | Mar. 31, 2021 | Sep. 30, 2020 | Jun. 30, 2020
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Securities, at fair value | $ 399,999,000 |  | $ 256,685,000 | $ 399,999,000 |  |  |  |  |  |
Minimum term of fixed rate mortgages underlying MBS |  |  | 15 years |  |  |  |  |  |  |
Maximum term of fixed rate mortgages underlying MBS |  |  | 30 years |  |  |  |  |  |  |
Allowance for credit loss | 86,833,000 | $ 218,011,000 | $ 39,447,000 | 86,833,000 | $ 3,025,000 | $ 44,102,000 | $ 54,261,000 | $ 63,244,000 | $ 106,246,000 | $ 136,589,000
Impairment and other gains and losses on securities available-for-sale and other assets |  |  | (33,956,000) | 425,082,000 | $ 180,000 |  |  |  |  |
Term Notes backed by MSR Related Collateral |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Securities, at fair value | 239,000,000 |  | 153,800,000 | 239,000,000 |  |  |  |  |  |
Amortized costs | 184,900,000 |  | 121,400,000 | 184,900,000 |  |  |  |  |  |
Gross unrealized gains | $ 54,000,000 |  | $ 32,400,000 | 54,000,000 |  |  |  |  |  |
Weighted average yield | 12.30% |  | 10.30% |  |  |  |  |  |  |
Weighted average to maturity | 8 years 8 months 12 days |  | 1 year 8 months 12 days |  |  |  |  |  |  |
Proceeds from Sale of Mortgage Servicing Rights (MSR) |  |  |  | 711,700,000 |  |  |  |  |  |
Gross realized losses |  |  |  | $ 28,700,000 |  |  |  |  |  |
Impairment |  | 280,800,000 |  |  |  |  |  |  |  |
Mortgage-backed Securities, Issued by Private Enterprises |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Securities, at fair value |  |  |  |  |  |  | $ 0 |  |  |
Gross unrealized losses |  |  | $ 0 |  |  |  |  |  |  |
Allowance for credit loss |  |  | $ 0 |  |  |  |  |  |  |
MBS and MSR-Related Assets |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Impairment and other gains and losses on securities available-for-sale and other assets |  | $ 63,500,000 |  |  |  |  |  |  |  |
Minimum | RPL/NPL MBS |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 3.00% |  |  |  |  |  |  |
Debt instrument, coupon step-up period |  |  | 36 months |  |  |  |  |  |  |
Maximum | RPL/NPL MBS |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, basis spread on variable rate |  |  | 4.00% |  |  |  |  |  |  |
Debt instrument, coupon step-up period |  |  | 48 months |  |  |  |  |  |  |

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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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- Definition The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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- Definition The cash inflow from the sale of servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. Rights may be obtained via (1) acquisition or assumption of a servicing obligation that does not relate to financial assets of the servicer or its consolidated affiliates; or (2) by originating mortgage loans and then (a) transferring the loans to a Variable Interest Entity (VIE) in a transaction that meets the necessary transfer and classification requirements, or (b) transferring the loans in a transaction that meets the requirements for sale accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3179-108585 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107207-111719 + Details
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