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Residential Mortgage Securities and MSR Related Assets (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items] |  |  |
Minimum term of fixed rate mortgages underlying MBS | 15 years |  |
Maximum term of fixed rate mortgages underlying MBS | 30 years |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | $ 18,818 |  |
Reclassification adjustment for OTTI included in net income | (180) | $ (1,259) | $ (1,032)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 417,089 | 484,591 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 18,818 | 63,783 |
Investment Owned, Balance, Principal Amount | 4,044,818 | 6,646,178 |
Agency MBS |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 18,709 |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 15,326 | 13,061 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 18,709 | 49,498 |
Investment Owned, Balance, Principal Amount | 1,604,583 | 2,630,630 |
RPL/NPL MBS |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Investment Owned, Balance, Principal Amount | 632,300 | 1,400,000 |
Non-Agency MBS |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss | 18 |  |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax | 395,459 | 458,985 |
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax | 18 | 8,389 |
Investment Owned, Balance, Principal Amount | $ 2,195,303 | $ 3,538,804 |
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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