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Mortgage-Backed Securities - Investment Type (Details) - USD ($) $ in Thousands | Mar. 31, 2023 | Dec. 31, 2022
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Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | $ 3,376,974 | $ 3,236,285
Amortized Cost |  | 3,634,434 | 3,522,256
Fair Value |  | 3,296,784 | 3,112,705
Amortized cost |  | 1,247,920 | 1,288,269
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 660 | 507
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (167,213) | (181,853)
Debt Securities, Available-for-sale |  | 1,081,367 | 1,106,923
Debt Securities, Trading, Amortized Cost |  | 2,386,513 | 2,233,987
Gross unrealized gain, investment, fair value option |  | 6,070 | 0
Gross unrealized loss, investment, fair value option |  | (177,166) | (228,205)
Debt Securities, Trading |  | 2,215,417 | 2,005,782
Residential Mortgage Backed Securities [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 3,251,563 | 3,104,498
Amortized Cost |  | 3,287,869 | 3,150,873
Fair Value |  | 2,966,891 | 2,762,878
Amortized cost |  | 960,952 | 977,624
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 | 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (153,711) | (164,949)
Debt Securities, Available-for-sale |  | 807,241 | 812,675
Debt Securities, Trading, Amortized Cost |  | 2,326,917 | 2,173,249
Gross unrealized gain, investment, fair value option |  | 6,070 | 0
Gross unrealized loss, investment, fair value option |  | (173,337) | (223,046)
Debt Securities, Trading |  | 2,159,650 | 1,950,203
Commercial Mortgage Backed Securities [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 125,220 | 131,578
Amortized Cost |  | 125,833 | 132,333
Fair Value |  | 119,474 | 124,690
Amortized cost |  | 110,539 | 117,031
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 | 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (5,428) | (6,474)
Debt Securities, Available-for-sale |  | 105,111 | 110,557
Debt Securities, Trading, Amortized Cost |  | 15,294 | 15,302
Gross unrealized gain, investment, fair value option |  | 0 | 0
Gross unrealized loss, investment, fair value option |  | (931) | (1,169)
Debt Securities, Trading |  | 14,363 | 14,133
Interest-Only-Strip [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Amortized Cost | [1] | 220,541 | 238,841
Fair Value | [1] | 210,283 | 224,985
Amortized cost |  | 176,238 | 193,405
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 660 | 507
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (8,019) | (10,373)
Debt Securities, Available-for-sale |  | 168,879 | 183,539
Debt Securities, Trading, Amortized Cost |  | 44,302 | 45,436
Gross unrealized gain, investment, fair value option |  | 0 | 0
Gross unrealized loss, investment, fair value option |  | (2,898) | (3,990)
Debt Securities, Trading |  | 41,404 | 41,446
Interest-Only-Strip, Agency CMBS [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Notional balance |  | 9,017,704 | 9,711,981
Interest-Only-Strip, Non-Agency CMBS [Member] |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Notional balance |  | 5,019,210 | 6,280,761
Non-Agency MBS |  |  |
Debt Securities, Trading and Available-for-sale [Abstract] |  |  |
Par Value |  | 191 | 209
Fair Value |  | 136 | 152
Amortized cost |  | 191 | 209
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax |  | 0 | 0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax |  | (55) | (57)
Debt Securities, Available-for-sale |  | $ 136 | $ 152
[1] | (1) The notional balance for Agency CMBS IO and non-Agency CMBS IO was $9,017,704 and $5,019,210, respectively, as of March 31, 2023, and $9,711,981 and $6,280,761, respectively, as of December 31, 2022.

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