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Mortgage-Backed Securities Narrative (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
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Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Catch-up Premium Amortization Adjustment | $ (0.4) | $ (0.7) | $ (0.1) | $ 1.6

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- Definition For securities whose cash flows vary depending on prepayments, an effective yield retroactive to the time of purchase is periodically recomputed based on actual prepayments and changes in projected prepayment activity, and a catch-up adjustment, or "Catch-up Premium Amortization Adjustment," is made to amortization to reflect the cumulative impact of the change in effective yield. + References No definition available. + Details
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- References No definition available. + Details
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