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Residential Mortgage Securities and MSR-Related Assets (Impact of AFS Securities on AOCI) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
AOCI from AFS Securities: |  |
Unrealized gain on AFS securities at beginning of period | $ 392,722 | $ 417,167
Unrealized (loss)/gain on AFS securities, net | 124,410 | 22,103
Reclassification adjustment for MBS sales included in net income | (23,953) | (17,009)
Reclassification adjustment for impairment included in net income | (344,269) | 0
Change in AOCI from AFS securities | (243,812) | 5,094
Balance at end of period | 148,910 | 422,261
Agency MBS |  |
AOCI from AFS Securities: |  |
Unrealized (loss)/gain on AFS securities, net | 4,876 | 9,315
Non-Agency MBS |  |
AOCI from AFS Securities: |  |
Unrealized (loss)/gain on AFS securities, net | 124,700 | 12,276
MSR-related assets |  |
AOCI from AFS Securities: |  |
Unrealized (loss)/gain on AFS securities, net | $ (5,166) | $ 512

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