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Mortgage-Backed Securities - Investment Type (Details) - USD ($) $ in Thousands | Sep. 30, 2024 | Dec. 31, 2023
--- | --- | ---
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | $ 7,355,891 | $ 6,143,945
Amortized Cost |  | 7,468,566 | 6,283,185
Non-Agency other, Amortized Cost |  | 1,036,447 | 1,131,769
Fair Value |  | 7,327,643 | 6,038,948
Gross Unrealized Gain |  | 1,913 | 1,324
Gross Unrealized Loss |  | (137,802) | (159,826)
Fair Value |  | 900,558 | 973,267
Amortized Cost |  | 6,432,119 | 5,151,416
Gross Unrealized Gain |  | 98,269 | 48,461
Gross Unrealized Loss |  | (103,303) | (134,196)
Fair Value |  | 6,427,085 | 5,065,681
Residential Mortgage Backed Securities [Member] | Agency MBS |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 7,254,934 | 6,022,502
Amortized Cost |  | 7,239,866 | 5,993,922
Non-Agency other, Amortized Cost |  | 844,694 | 898,420
Fair Value |  | 7,105,090 | 5,763,532
Gross Unrealized Gain |  | 0 | 0
Gross Unrealized Loss |  | (131,398) | (148,606)
Fair Value |  | 713,296 | 749,814
Amortized Cost |  | 6,395,172 | 5,095,502
Gross Unrealized Gain |  | 98,267 | 48,459
Gross Unrealized Loss |  | (101,645) | (130,243)
Fair Value |  | 6,391,794 | 5,013,718
Commercial Mortgage Backed Securities [Member] | Agency MBS |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 100,957 | 121,293
Amortized Cost |  | 101,169 | 121,799
Non-Agency other, Amortized Cost |  | 101,169 | 106,527
Fair Value |  | 98,026 | 115,595
Gross Unrealized Gain |  | 8 | 28
Gross Unrealized Loss |  | (3,151) | (5,159)
Fair Value |  | 98,026 | 101,396
Amortized Cost |  |  | 15,272
Gross Unrealized Gain |  |  | 0
Gross Unrealized Loss |  |  | (1,073)
Fair Value |  |  | 14,199
Interest-Only-Strip [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Amortized Cost | [1] | 127,531 | 167,314
Non-Agency other, Amortized Cost |  | 90,584 | 126,672
Fair Value | [1] | 124,527 | 159,718
Gross Unrealized Gain |  | 1,905 | 1,296
Gross Unrealized Loss |  | (3,253) | (6,014)
Fair Value |  | 89,236 | 121,954
Amortized Cost |  | 36,947 | 40,642
Gross Unrealized Gain |  | 2 | 2
Gross Unrealized Loss |  | (1,658) | (2,880)
Fair Value |  | 35,291 | 37,764
Interest-Only-Strip, Agency CMBS [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 6,802,508 | 7,723,379
Interest-Only-Strip, Non-Agency CMBS [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 2,784,032 | 3,860,007
Non-Agency MBS |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 0 | 150
Non-Agency other, Amortized Cost |  | 0 | 150
Gross Unrealized Gain |  |  | 0
Gross Unrealized Loss |  |  | (47)
Fair Value |  | $ 0 | $ 103
[1] | (1) The notional balance for Agency CMBS IO and non-Agency CMBS IO was $6,802,508 and $2,784,032, respectively, as of September 30, 2024, and $7,723,379 and $3,860,007, respectively, as of December 31, 2023.

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