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Investment Securities - Narrative (Details) - security | Mar. 31, 2019 | Dec. 31, 2018
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Investments, Debt and Equity Securities [Abstract] |  |
Number of investment securities in unrealized loss position | 175 | 229
Number of investment securities in unrealized loss position longer than 12 months | 154 |
Number of investment securities in unrealized loss position less than 12 months | 21 |

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