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Securities - Unrealized Gains (Losses) of Debt Securities (Details) - USD ($) $ in Thousands | Sep. 30, 2018 | Jan. 01, 2018 | Dec. 31, 2017
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Investments, Debt and Equity Securities [Abstract] |  |  |  |
Total unrealized gains/(losses) on debt securities available-for-sale, Gross Unrealized Gains | $ 1,960 |  | $ 5,645 | [1]
Total unrealized gains/(losses) on debt securities available-for-sale, Gross Unrealized Losses | (15,573) |  | (3,967) | [1]
Total unrealized gains/(losses) on debt securities available-for-sale, Net Unrealized (Losses)/Gains | (13,613) |  | 1,678 | [1]
Income tax (expense) benefit, Gross Unrealized Gains | (416) |  | (1,982) |
Income tax (expense) benefit, Gross Unrealized Losses | 3,307 |  | 1,393 |
Income tax (expense) benefit, Net Unrealized (Losses)/Gains | 2,891 |  | (589) |
Net Unrealized (Losses)/Gains, Net of Tax Included in Accumulated Other Comprehensive Loss, Gross Unrealized Gains | 1,544 |  | 3,663 |
Net Unrealized (Losses)/Gains, Net of Tax Included in Accumulated Other Comprehensive Loss, Gross Unrealized Losses | (12,266) |  | (2,574) |
Net Unrealized (Losses)/Gains, Net of Tax Included in Accumulated Other Comprehensive Loss, Net Unrealized (Losses)/Gains | $ (10,722) |  | 1,089 |
Retained Earnings | ASU No. 2016-01 |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Reclassification of net unrealized gains on equity securities (from) AOCI to Retained Earnings |  | $ 900 | 862 | [2]
AOCI | ASU No. 2016-01 |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |
Reclassification of net unrealized gains on equity securities (from) AOCI to Retained Earnings |  | $ (900) | $ (862) | [2]
[1] | Gross unrealized gains and losses of $862 at December 31, 2017 have been restated to reflect the reclassifications from OCI to retained earnings due to the adoption of ASU No. 2016-01
[2] | Reclassification due to the adoption of ASU No. 2016-01.

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