| **Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands** | 3 Months Ended | 6 Months Ended |           |
|----------------------------------------------------------------------------------------------------------|----------------|----------------|-----------|
||
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | $ 119,990      |           | $ 119,990 |   | $ 134,581 |
| Impaired loans with related allowance                                                                    | 6,844          |           | 6,844     |   | 7,953 |
| Total Impaired Loans                                                                                     | 126,834        |           | 126,834   |   | 142,534 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 81,449         |           | 81,449    |   | 90,975 |
| Impaired loans with related allowance                                                                    | 6,194          |           | 6,194     |   | 6,552 |
| Total Impaired Loans                                                                                     | 87,643         |           | 87,643    |   | 97,527 |
| Related Allowance                                                                                        | 2,120          |           | 2,120     |   | 1,842 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 82,671         | $ 95,074       | 83,928    | $ 96,498 |   |
| Impaired loans with related allowance                                                                    | 6,267          | 8,426          | 6,402     | 8,544 |   |
| Total Impaired Loans                                                                                     | 88,938         | 103,500        | 90,330    | 105,042 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 1,119          | 1,157          | 2,193     | 2,263 |   |
| Impaired loans with related allowance                                                                    | 9              | 10             | 19        | 19 |   |
| Total Impaired Loans                                                                                     | 1,128          | 1,167          | 2,212     | 2,282 |   |
| Commercial and industrial loans                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 19,322         |           | 19,322    |   | 22,151 |
| Impaired loans with related allowance                                                                    | 2,491          |           | 2,491     |   | 3,043 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 10,183         |           | 10,183    |   | 11,669 |
| Impaired loans with related allowance                                                                    | 2,114          |           | 2,114     |   | 2,690 |
| Related Allowance                                                                                        | 1,007          |           | 1,007     |   | 1,247 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 10,372         | 12,154         | 10,307    | 12,942 |   |
| Impaired loans with related allowance                                                                    | 2,120          | 3,204          | 2,129     | 3,214 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 128            | 111            | 231       | 200 |   |
| Impaired loans with related allowance                                                                    | 9              | 10             | 19        | 19 |   |
| Agricultural production financing and other loans to farmers                                             |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 709            |           | 709       |   | 370 |
| Impaired loans with related allowance                                                                    | 1,331          |           | 1,331     |   | 466 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 701            |           | 701       |   | 361 |
| Impaired loans with related allowance                                                                    | 1,301          |           | 1,301     |   | 466 |
| Related Allowance                                                                                        | 566            |           | 566       |   | 30 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 834            | 1,325          | 882       | 1,343 |   |
| Impaired loans with related allowance                                                                    | 1,321          |           | 1,405     |   |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 2              |                | 2         |   |   |
| Impaired loans with related allowance                                                                    |                |           |      |   |   |
| Real estate loans - Construction                                                                         |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 8,089          |           | 8,089     |   | 4,551 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 4,091          |           | 4,091     |   | 2,336 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 4,085          | 7,648          | 4,074     | 7,898 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 74             | 95             | 147       | 191 |   |
| Real estate loans - Commercial and farmland                                                              |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 83,028         |           | 83,028    |   | 95,930 |
| Impaired loans with related allowance                                                                    | 2,145          |           | 2,145     |   | 2,144 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 61,319         |           | 61,319    |   | 69,024 |
| Impaired loans with related allowance                                                                    | 1,978          |           | 1,978     |   | 1,933 |
| Related Allowance                                                                                        | 456            |           | 456       |   | 392 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 62,173         | 66,625         | 63,136    | 66,957 |   |
| Impaired loans with related allowance                                                                    | 1,986          | 2,622          | 2,008     | 2,727 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 861            | 894            | 1,706     | 1,765 |   |
| Impaired loans with related allowance                                                                    |                |                |           |  |   |
| Real estate loans - Residential                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 8,650          |           | 8,650     |   | 11,262 |
| Impaired loans with related allowance                                                                    | 877            |           | 877       |   | 2,300 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 5,016          |           | 5,016     |   | 7,338 |
| Impaired loans with related allowance                                                                    | 801            |           | 801       |   | 1,463 |
| Related Allowance                                                                                        | 91             |           | 91        |   | 173 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 5,069          | 7,114          | 5,390     | 7,150 |   |
| Impaired loans with related allowance                                                                    | 840            | 2,600          | 860       | 2,603 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 54             | 57             | 107       | 107 |   |
| Impaired loans with related allowance                                                                    |                |                |           |   |   |
| Real estate loans - Home equity                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 176            |           | 176       |   | 297 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 139            |           | 139       |   | 247 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 138            | 208            | 139       | $ 208 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 |                |                |      |   |   |
| Other commercial loans                                                                                   |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 16             |           | 16        |   | 20 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 |                |           |           |   |  |

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