| **Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Details) - USD ($) $ in Thousands** | Jun. 30, 2019 | Dec. 31, 2018 |
|-------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | $ 7,511,370   | $ 7,224,467   |
| Commercial and industrial loans                                                                             |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 1,877,042     | 1,726,664     |
| Agricultural production financing and other loans to farmers                                                |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 83,452        | 92,404        |
| Construction                                                                                                |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 624,548       | 545,729       |
| Commercial and farmland                                                                                     |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 2,821,689     | 2,832,102     |
| Residential                                                                                                 |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 993,802       | 966,421       |
| Home equity                                                                                                 |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 548,006       | 528,157       |
| Individuals' loans for household and other personal expenditures                                            |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 98,384        | 99,788        |
| Public finance and other commercial loans                                                                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 464,447       | 433,202       |
| Commercial Pass                                                                                             |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 5,734,217     | 5,528,751     |
| Commercial Pass | Commercial and industrial loans                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 1,781,040     | 1,660,879     |
| Commercial Pass | Agricultural production financing and other loans to farmers                              |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 67,837        | 78,446        |
| Commercial Pass | Construction                                                                              |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 591,962       | 492,358       |
| Commercial Pass | Commercial and farmland                                                                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 2,645,338     | 2,669,491     |
| Commercial Pass | Residential                                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 156,622       | 170,075       |
| Commercial Pass | Home equity                                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 27,324        | 24,653        |
| Commercial Pass | Individuals' loans for household and other personal expenditures                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Pass | Public finance and other commercial loans                                                 |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 464,094       | 432,849       |
| Commercial Special Mention                                                                                  |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 146,333       | 115,342       |
| Commercial Special Mention | Commercial and industrial loans                                                |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 53,407        | 23,246        |
| Commercial Special Mention | Agricultural production financing and other loans to farmers                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 5,478         | 5,966         |
| Commercial Special Mention | Construction                                                                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 1,444         | 2,185         |
| Commercial Special Mention | Commercial and farmland                                                        |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 79,586        | 76,037        |
| Commercial Special Mention | Residential                                                                    |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 5,833         | 7,373         |
| Commercial Special Mention | Home equity                                                                    |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 585           | 535           |
| Commercial Special Mention | Individuals' loans for household and other personal expenditures               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Special Mention | Public finance and other commercial loans                                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Substandard                                                                                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 158,830       | 161,929       |
| Commercial Substandard | Commercial and industrial loans                                                    |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 42,266        | 42,539        |
| Commercial Substandard | Agricultural production financing and other loans to farmers                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 10,137        | 7,992         |
| Commercial Substandard | Construction                                                                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 7,712         | 24,224        |
| Commercial Substandard | Commercial and farmland                                                            |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 94,179        | 84,288        |
| Commercial Substandard | Residential                                                                        |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 3,425         | 2,076         |
| Commercial Substandard | Home equity                                                                        |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 758           | 457           |
| Commercial Substandard | Individuals' loans for household and other personal expenditures                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Substandard | Public finance and other commercial loans                                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 353           | 353           |
| Commercial Doubtful                                                                                         |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 779           | 0             |
| Commercial Doubtful | Commercial and industrial loans                                                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 329           | 0             |
| Commercial Doubtful | Agricultural production financing and other loans to farmers                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Doubtful | Construction                                                                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Doubtful | Commercial and farmland                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 450           | 0             |
| Commercial Doubtful | Residential                                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Doubtful | Home equity                                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Doubtful | Individuals' loans for household and other personal expenditures                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Doubtful | Public finance and other commercial loans                                             |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss                                                                                             |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Commercial and industrial loans                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Agricultural production financing and other loans to farmers                              |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Construction                                                                              |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Commercial and farmland                                                                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Residential                                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Home equity                                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Individuals' loans for household and other personal expenditures                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Commercial Loss | Public finance and other commercial loans                                                 |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Performing                                                                                         |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 1,464,815     | 1,410,521     |
| Consumer Performing | Commercial and industrial loans                                                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Performing | Agricultural production financing and other loans to farmers                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Performing | Construction                                                                          |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 23,430        | 25,419        |
| Consumer Performing | Commercial and farmland                                                               |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 2,136         | 2,285         |
| Consumer Performing | Residential                                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 823,309       | 782,080       |
| Consumer Performing | Home equity                                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 517,620       | 500,996       |
| Consumer Performing | Individuals' loans for household and other personal expenditures                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 98,320        | 99,741        |
| Consumer Performing | Public finance and other commercial loans                                             |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Non-Performing                                                                                     |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 6,396         | 7,924         |
| Consumer Non-Performing | Commercial and industrial loans                                                   |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Non-Performing | Agricultural production financing and other loans to farmers                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 0             |
| Consumer Non-Performing | Construction                                                                      |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       |               | 1,543         |
| Consumer Non-Performing | Commercial and farmland                                                           |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 0             | 1             |
| Consumer Non-Performing | Residential                                                                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 4,613         | 4,817         |
| Consumer Non-Performing | Home equity                                                                       |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 1,719         | 1,516         |
| Consumer Non-Performing | Individuals' loans for household and other personal expenditures                  |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | 64            | 47            |
| Consumer Non-Performing | Public finance and other commercial loans                                         |          |          |
| **Financing Receivable, Credit Quality Indicator [Line Items]**                                             |          |          |
| Loans                                                                                                       | $ 0           | $ 0           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522
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