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Securities (Details Textual) - USD ($) $ in Thousands | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Gain on sale of investments | $ 0 | $ (2) |  |
Gross unrealized losses | 17,855 |  | $ 9,535 |
Cumulative OTTI charges | 7,132 | $ 7,132 | 7,132 | $ 13,974
Amortized Cost | 812,002 |  | 811,369 |
Securities available-for-sale | $ 805,558 |  | $ 814,931 |
Minimum [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Basis point spread on variable rate | 1.60% |  |  |
Minimum [Member] | Standard Poors [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Credit Quality Indicator Pricing | 73.69 |  |  |
Minimum [Member] | Moody Investor Service [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Credit Quality Indicator Pricing | 20.96 |  |  |
Maximum [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Basis point spread on variable rate | 1.80% |  |  |
Maximum [Member] | Standard Poors [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Credit Quality Indicator Pricing | 83.88 |  |  |
Maximum [Member] | Moody Investor Service [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Credit Quality Indicator Pricing | 49.56 |  |  |

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
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