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Fair Value of Financial Instruments (Fair Value Methodology) (Details) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2021 USD ($) | Sep. 30, 2020 USD ($) | Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Residential whole loans, at fair value | $ 1,207,731 |  | $ 1,216,637
Purchases excluded from level 2 fair value | 112,500 |  | 265
Discounted cash flow |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Residential whole loans, at fair value | 798,185 |  | 789,576
Liquidation model |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Residential whole loans, at fair value | 409,546 |  | 427,061
Simple average amount | $ 403 |  | $ 380
Residential whole loans, at fair value | Level 3 | Liquidation model | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value Inputs, Annual Change in Home Prices | 4.20% |  | 0.00%
Liquidation timeline (in years) | 8 months 12 days |  | 9 months 18 days
Fair Value Inputs, Value of Underlying Property | $ 5 |  | $ 12
Residential whole loans, at fair value | Level 3 | Liquidation model | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value Inputs, Annual Change in Home Prices | 10.40% |  | 6.50%
Liquidation timeline (in years) | 4 years 9 months 18 days |  | 4 years 9 months 18 days
Fair Value Inputs, Value of Underlying Property | $ 3,704 |  | $ 4,500
Discount rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.033 |  | 0.033
Discount rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.080 |  | 0.080
Discount rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.038 |  | 0.039
Discount rate | Residential whole loans, at fair value | Level 3 | Liquidation model | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.067 |  | 0.067
Discount rate | Residential whole loans, at fair value | Level 3 | Liquidation model | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.500 |  | 0.500
Discount rate | Residential whole loans, at fair value | Level 3 | Liquidation model | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.081 |  | 0.081
Prepayment rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.007 |  | 0.000
Prepayment rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.089 |  | 0.099
Prepayment rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.042 |  | 0.048
Prepayment rate | Residential whole loans, at fair value | Level 3 | Liquidation model | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value Inputs, Annual Change in Home Prices | 6.20% | 3.60% |
Default rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.000 |  | 0.000
Default rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.179 |  | 0.189
Default rate | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.034 |  | 0.038
Default rate | Residential whole loans, at fair value | Level 3 | Liquidation model | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Liquidation timeline (in years) | 1 year 9 months 18 days | 1 year 9 months 18 days |
Loss severity | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Minimum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.000 |  | 0.000
Loss severity | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Maximum |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 1.000 |  | 1.000
Loss severity | Residential whole loans, at fair value | Level 3 | Discounted cash flow | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Measurement input | 0.121 |  | 0.127
Loss severity | Residential whole loans, at fair value | Level 3 | Liquidation model | Weighted Average |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair Value Inputs, Value of Underlying Property | $ 744 | $ 729 |

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