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Residential Mortgage Securities and MSR-Related Assets (Residential and Mortgage Securities) (Details) - USD ($) | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face | $ 161,878,000 | $ 4,044,818,000
Purchase Premiums | 3,022,000 | 67,108,000
Accretable Purchase Discounts | (8,206,000) | (90,694,000)
Discount Designated as Credit Reserve | (21,437,000) | (436,598,000)
Gross Amortized Cost | 135,257,000 | 3,585,248,000
Gross Unrealized Gains | 26,926,000 | 417,089,000
Gross Unrealized Losses | (1,183,000) | (18,818,000)
Net Unrealized Gain/(Loss) | 25,743,000 | 398,271,000
Fair Value | 161,000,000 | 3,983,519,000
Principal payments receivable |  | 614,000
Non-Agency MBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face | 57,847,000 | 2,195,303,000
Purchase Premiums | 0 | 0
Accretable Purchase Discounts | (8,136,000) | (90,617,000)
Discount Designated as Credit Reserve | (669,000) | (436,598,000)
Gross Amortized Cost | 49,042,000 | 1,668,088,000
Gross Unrealized Gains | 8,585,000 | 395,459,000
Gross Unrealized Losses | (861,000) | (18,000)
Net Unrealized Gain/(Loss) | 7,724,000 | 395,441,000
Fair Value | $ 56,766,000 | 2,063,529,000
Expected to Recover Par |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 722,477,000
Purchase Premiums |  | 0
Accretable Purchase Discounts |  | (16,661,000)
Discount Designated as Credit Reserve |  | 0
Gross Amortized Cost |  | 705,816,000
Gross Unrealized Gains |  | 19,861,000
Gross Unrealized Losses |  | (9,000)
Net Unrealized Gain/(Loss) |  | 19,852,000
Fair Value |  | 725,668,000
Expected to Recover Less Than Par |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 1,472,826,000
Purchase Premiums |  | 0
Accretable Purchase Discounts |  | (73,956,000)
Discount Designated as Credit Reserve |  | (436,598,000)
Gross Amortized Cost |  | 962,272,000
Gross Unrealized Gains |  | 375,598,000
Gross Unrealized Losses |  | (9,000)
Net Unrealized Gain/(Loss) |  | 375,589,000
Fair Value |  | $ 1,337,861,000
Percentage of current face amount of Non-Agency MBS to be recovered | 99.00% | 80.00%
Agency MBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | $ 1,604,583,000
Purchase Premiums |  | 62,790,000
Accretable Purchase Discounts |  | (22,000)
Discount Designated as Credit Reserve |  | 0
Gross Amortized Cost |  | 1,667,965,000
Gross Unrealized Gains |  | 15,326,000
Gross Unrealized Losses |  | (18,709,000)
Net Unrealized Gain/(Loss) |  | (3,383,000)
Fair Value |  | 1,664,582,000
Agency MBS | Fannie Mae |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 1,119,708,000
Purchase Premiums |  | 43,249,000
Accretable Purchase Discounts |  | (22,000)
Discount Designated as Credit Reserve |  | 0
Gross Amortized Cost |  | 1,162,935,000
Gross Unrealized Gains |  | 9,799,000
Gross Unrealized Losses |  | (14,741,000)
Net Unrealized Gain/(Loss) |  | (4,942,000)
Fair Value |  | 1,157,993,000
Agency MBS | Freddie Mac |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 480,879,000
Purchase Premiums |  | 19,468,000
Accretable Purchase Discounts |  | 0
Discount Designated as Credit Reserve |  | 0
Gross Amortized Cost |  | 500,961,000
Gross Unrealized Gains |  | 5,475,000
Gross Unrealized Losses |  | (3,968,000)
Net Unrealized Gain/(Loss) |  | 1,507,000
Fair Value |  | 502,468,000
Agency MBS | Ginnie Mae |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 3,996,000
Purchase Premiums |  | 73,000
Accretable Purchase Discounts |  | 0
Discount Designated as Credit Reserve |  | 0
Gross Amortized Cost |  | 4,069,000
Gross Unrealized Gains |  | 52,000
Gross Unrealized Losses |  | 0
Net Unrealized Gain/(Loss) |  | 52,000
Fair Value |  | 4,121,000
Total MBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face |  | 3,799,886,000
Purchase Premiums |  | 62,790,000
Accretable Purchase Discounts |  | (90,639,000)
Discount Designated as Credit Reserve |  | (436,598,000)
Gross Amortized Cost |  | 3,336,053,000
Gross Unrealized Gains |  | 410,785,000
Gross Unrealized Losses |  | (18,727,000)
Net Unrealized Gain/(Loss) |  | 392,058,000
Fair Value |  | 3,728,111,000
CRT securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face | $ 104,031,000 | 244,932,000
Purchase Premiums | 3,022,000 | 4,318,000
Accretable Purchase Discounts | (70,000) | (55,000)
Discount Designated as Credit Reserve | (20,768,000) | 0
Gross Amortized Cost | 86,215,000 | 249,195,000
Gross Unrealized Gains | 18,341,000 | 6,304,000
Gross Unrealized Losses | (322,000) | (91,000)
Net Unrealized Gain/(Loss) | 18,019,000 | 6,213,000
Fair Value | 104,234,000 | 255,408,000
RPL/NPL MBS |  |
Debt Securities, Available-for-sale [Line Items] |  |
Principal/ Current Face | 55,000,000.0 | 632,300,000
Gross Amortized Cost | 46,900,000 | 631,800,000
Fair Value | 53,900,000 | 635,000,000.0
CRT, Fair Value Option |  |
Debt Securities, Available-for-sale [Line Items] |  |
Gross Unrealized Gains | 551,000 | 6,300,000
Gross Unrealized Losses | (322,000) | (91,000)
Fair Value | $ 66,200,000 | 255,400,000
Agency MBS, Fair Value Option |  |
Debt Securities, Available-for-sale [Line Items] |  |
Gross Unrealized Gains |  | 4,500,000
Gross Unrealized Losses |  | 0
Debt securities, fair value option |  | $ 280,300,000

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