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Securities, at Fair Value (Impact of AFS Securities on AOCI) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
AOCI from AFS Securities: |  |  |  |
Unrealized gain on AFS securities at beginning of period | $ 66,163 | $ 52,889 | $ 79,607 | $ 392,722
Unrealized (loss)/gain on AFS securities, net | (8,029) | 15,082 | (21,473) | 408,585
Reclassification adjustment for MBS sales included in net income | 0 | (60) | 0 | (389,127)
Reclassification adjustment for impairment included in net income | 0 | 0 | 0 | (344,269)
Change in AOCI from AFS securities | (8,029) | 15,022 | (21,473) | (324,811)
Balance at end of period | 58,134 | 67,911 | 58,134 | 67,911
Agency MBS |  |  |  |
AOCI from AFS Securities: |  |  |  |
Unrealized (loss)/gain on AFS securities, net | $ (8,029) | $ 15,082 | $ (21,473) | $ 408,585

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