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Securities (Details Textual) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017 | Jun. 30, 2018 | Dec. 31, 2017 | Jun. 30, 2017 | Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |
Gain on sale of investments | $ (3) | $ (27) | $ (5) | $ (44) |  |  |  |
Gross unrealized losses | 23,412 |  | 23,412 |  |  | $ 9,535 |  |
Cumulative OTTI charges | 2,974 | $ 7,132 | 2,974 | $ 7,132 | $ 2,974 | 7,132 | $ 7,132 | $ 13,974
Amortized Cost | 803,271 |  | 803,271 |  |  | 811,369 |  |
Securities available-for-sale | $ 785,693 |  | $ 785,693 |  |  | $ 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 | 85.57 |  | 85.57 |  |  |  |  |
Minimum [Member] | Moody Investor Service [Member] |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |
Credit Quality Indicator Pricing | 21.23 |  | 21.23 |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |
Basis point spread on variable rate | 1.80% |  | 1.80% |  |  |  |  |

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