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Securities (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Gain on sale of investments | $ (2) | $ (15) | $ (2) | $ (17) |  |
Gross unrealized losses | 19,768 |  | 19,768 |  | $ 9,535 |
Cumulative OTTI charges | 2,974 | $ 7,132 | 2,974 | $ 7,132 | 7,132 | $ 7,132
Amortized Cost | 795,380 |  | 795,380 |  | 811,369 |
Securities available-for-sale | $ 782,609 |  | $ 782,609 |  | $ 814,931 |
Minimum [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Basis point spread on variable rate | 1.60% |  | 1.60% |  |  |
Minimum [Member] | Standard Poors [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Credit Quality Indicator Pricing | 86.26 |  | 86.26 |  |  |
Minimum [Member] | Moody Investor Service [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Credit Quality Indicator Pricing | 21.40 |  | 21.40 |  |  |
Maximum [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Basis point spread on variable rate | 1.80% |  | 1.80% |  |  |
Maximum [Member] | Standard Poors [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Credit Quality Indicator Pricing | 83.88 |  | 83.88 |  |  |
Maximum [Member] | Moody Investor Service [Member] |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |
Credit Quality Indicator Pricing | 49.56 |  | 49.56 |  |  |

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