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Residential Whole Loans (Narrative) (Details) - USD ($) | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2020 | Dec. 31, 2019
Receivables [Abstract] |  |  |  |  |
Total residential whole loans | $ 5,600,000,000 |  |  | $ 5,600,000,000 | $ 7,400,000,000
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Loss on sale of financing receivable | (800,000) |  |  |  |
Valuation allowance adjustment |  | $ 70,181,000 | $ (70,181,000) |  |
Interest income |  |  |  | 0 |
Unpaid principal balance of loans | 24,100,000 |  |  | 24,100,000 |
Non-QM Loans |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Financing receivable, sale |  |  |  | 1,800,000,000 |
Loss on sale of financing receivable |  |  |  | 273,000,000.0 |
Valuation allowance adjustment |  | 70,181,000 | (70,181,000) |  |
Purchased Performing Loans |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Financing receivable, nonaccrual | 345,600,000 |  |  | 345,600,000 | $ 99,900,000
Purchased Credit Deteriorated Loans |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Valuation allowance adjustment |  | $ 0 | $ 0 |  |
Financing receivable, nonaccrual | 148,700,000 |  |  | 148,700,000 |
Without Associated Credit Losses |  |  |  |  |
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |  |  |
Financing receivable, nonaccrual | $ 134,800,000 |  |  | $ 134,800,000 |

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