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Securities - Fair Values and Amortized Costs Securities (Details) - USD ($) $ in Thousands | 9 Months Ended |
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | $ 690,834 |  |  |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 1,960 |  | $ 5,645 | [1]
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (15,573) |  | (3,967) | [1]
Debt Securities, Available-for-Sale, Fair Value |  | 677,221 |  | 693,147 |
Equity Securities, Fair Value |  | 5,314 |  | 5,144 |
Total Securities, Amortized Cost |  |  |  | 695,284 |
Total Securities, Gross Unrealized Gains |  |  |  | 6,975 |
Total Securities, Gross Unrealized Losses |  |  |  | (3,968) |
Total Securities, Fair Value |  | 682,535 |  | 698,291 |
U.S. Treasury securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 9,956 |  | 19,943 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 0 |  | 0 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (400) |  | (154) |
Debt Securities, Available-for-Sale, Fair Value |  | 9,556 |  | 19,789 |
Obligations of U.S. government corporations and agencies |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 139,272 |  | 162,045 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 0 |  | 341 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (2,288) |  | (193) |
Debt Securities, Available-for-Sale, Fair Value |  | 136,984 |  | 162,193 |
Collateralized mortgage obligations of U.S. government corporations and agencies |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 141,283 |  | 109,916 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 0 |  | 93 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (3,623) |  | (1,321) |
Debt Securities, Available-for-Sale, Fair Value |  | 137,660 |  | 108,688 |
Residential mortgage-backed securities of U.S. government corporations and agencies |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 26,837 |  | 32,388 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 219 |  | 679 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (606) |  | (213) |
Debt Securities, Available-for-Sale, Fair Value |  | 26,450 |  | 32,854 |
Commercial mortgage-backed securities of U.S. government corporations and agencies |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 253,090 |  | 244,018 | [2]
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 0 |  | 247 | [2]
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (8,494) |  | (2,044) | [2]
Debt Securities, Available-for-Sale, Fair Value |  | 244,596 |  | 242,221 | [2]
Securities purchased pending settlement |  |  |  | 5,900 |
Obligations of states and political subdivisions |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 120,396 |  | 123,159 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 1,741 |  | 4,285 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (162) |  | (42) |
Debt Securities, Available-for-Sale, Fair Value |  | 121,975 |  | 127,402 |
Total Debt Securities Available-for-Sale |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Debt Securities, Available-for-Sale, Amortized Cost |  | 690,834 |  | 691,469 |
Debt Securities, Available-for-Sale, Gross Unrealized Gains |  | 1,960 |  | 5,645 |
Debt Securities, Available-for-Sale, Gross Unrealized Losses |  | (15,573) |  | (3,967) |
Debt Securities, Available-for-Sale, Fair Value |  | 677,221 |  | 693,147 |
Marketable equity securities |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |
Equity Securities, FV-NI, Cost | [3] | 0 |  | 3,815 |
Equity Securities, FV-NI, Unrealized Gain | [3] | 0 | $ 1,330 |  |
Equity Securities, FV-NI, Unrealized Loss | [3] | 0 | $ (1) |  |
Equity Securities, Fair Value | [3] | $ 0 |  | $ 5,144 |
[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] | Includes a $5.9 million security purchase that was pending settlement as of December 31, 2017.
[3] | ASU No. 2016-01 was adopted January 1, 2018, resulting in separate classification of our marketable equity securities previously included in available-for-sale securities.

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