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Residential Mortgage Securities and MSR-Related Assets (Impact of AFS Securities on AOCI) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
AOCI from AFS Securities: |  |  |  |
Unrealized gain on AFS securities at beginning of period | $ 52,889 | $ 439,898 | $ 392,722 | $ 417,167
Unrealized (loss)/gain on AFS securities, net | 15,082 | 5,483 | 408,585 | 50,085
Reclassification adjustment for MBS sales included in net income | (60) | (14,499) | (389,127) | (36,370)
Reclassification adjustment for impairment included in net income | 0 | 0 | (344,269) | 0
Change in AOCI from AFS securities | 15,022 | (9,016) | (324,811) | 13,715
Balance at end of period | 67,911 | 430,882 | 67,911 | 430,882
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] |  |  |  |
AOCI from AFS Securities: |  |  |  |
Unrealized (loss)/gain on AFS securities, net | 0 | 603 | (161) | 22,483
Non-Agency MBS |  |  |  |
AOCI from AFS Securities: |  |  |  |
Unrealized (loss)/gain on AFS securities, net | 5,998 | 2,856 | 360,315 | 22,211
MSR-related assets |  |  |  |
AOCI from AFS Securities: |  |  |  |
Unrealized (loss)/gain on AFS securities, net | $ 9,084 | $ 2,024 | $ 48,431 | $ 5,391

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