| **Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) - USD ($) $ in Thousands** | 3 Months Ended | 9 Months Ended |           |
|----------------------------------------------------------------------------------------------------------|----------------|----------------|-----------|
||
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | $ 116,135      |           | $ 116,135 |   | $ 134,581 |
| Impaired loans with related allowance                                                                    | 4,100          |           | 4,100     |   | 7,953 |
| Total Impaired Loans                                                                                     | 120,235        |           | 120,235   |   | 142,534 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 80,666         |           | 80,666    |   | 90,975 |
| Impaired loans with related allowance                                                                    | 3,492          |           | 3,492     |   | 6,552 |
| Total Impaired Loans                                                                                     | 84,158         |           | 84,158    |   | 97,527 |
| Related Allowance                                                                                        | 1,336          |           | 1,336     |   | 1,842 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 81,215         | $ 88,801       | 83,884    | $ 91,561 |   |
| Impaired loans with related allowance                                                                    | 3,517          | 6,362          | 3,640     | 6,560 |   |
| Total Impaired Loans                                                                                     | 84,732         | 95,163         | 87,524    | 98,121 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 1,058          | 1,157          | 3,173     | 3,329 |   |
| Impaired loans with related allowance                                                                    | 6              | 10             | 6         | 29 |   |
| Total Impaired Loans                                                                                     | 1,064          | 1,167          | 3,179     | 3,358 |   |
| Commercial and industrial loans                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 18,096         |           | 18,096    |   | 22,151 |
| Impaired loans with related allowance                                                                    | 779            |           | 779       |   | 3,043 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 9,996          |           | 9,996     |   | 11,669 |
| Impaired loans with related allowance                                                                    | 467            |           | 467       |   | 2,690 |
| Related Allowance                                                                                        | 379            |           | 379       |   | 1,247 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 10,025         | 11,863         | 10,436    | 12,676 |   |
| Impaired loans with related allowance                                                                    | 469            | 2,731          | 471       | 2,774 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 89             | 137            | 261       | 368 |   |
| Impaired loans with related allowance                                                                    |                | 10             |           | 29 |   |
| Agricultural production financing and other loans to farmers                                             |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 649            |           | 649       |   | 370 |
| Impaired loans with related allowance                                                                    | 1,186          |           | 1,186     |   | 466 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 611            |           | 611       |   | 361 |
| Impaired loans with related allowance                                                                    | 1,156          |           | 1,156     |   | 466 |
| Related Allowance                                                                                        | 175            |           | 175       |   | 30 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 636            | 675            | 644       | 699 |   |
| Impaired loans with related allowance                                                                    | 1,164          | 547            | 1,236     | 547 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 3              |                | 3         |   |   |
| Impaired loans with related allowance                                                                    | 6              |                | 6         |  |   |
| Real estate loans - Construction                                                                         |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 6,492          |           | 6,492     |   | 4,551 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 3,545          |           | 3,545     |   | 2,336 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 3,526          | 2,855          | 3,572     | 3,407 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 72             | 41             | 215       | 123 |   |
| Real estate loans - Commercial and farmland                                                              |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 82,551         |           | 82,551    |   | 95,930 |
| Impaired loans with related allowance                                                                    | 2,070          |           | 2,070     |   | 2,144 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 61,536         |           | 61,536    |   | 69,024 |
| Impaired loans with related allowance                                                                    | 1,835          |           | 1,835     |   | 1,933 |
| Related Allowance                                                                                        | 760            |           | 760       |   | 392 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 61,903         | 64,186         | 63,722    | 65,310 |   |
| Impaired loans with related allowance                                                                    | 1,850          | 2,459          | 1,894     | 2,613 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 854            | 932            | 2,576     | 2,661 |   |
| Impaired loans with related allowance                                                                    |                |                |           |  |   |
| Real estate loans - Residential                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 8,252          |           | 8,252     |   | 11,262 |
| Impaired loans with related allowance                                                                    | 65             |           | 65        |   | 2,300 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 4,934          |           | 4,934     |   | 7,338 |
| Impaired loans with related allowance                                                                    | 34             |           | 34        |   | 1,463 |
| Related Allowance                                                                                        | 22             |           | 22        |   | 173 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 5,081          | 9,028          | 5,453     | 9,272 |   |
| Impaired loans with related allowance                                                                    | 34             | 625            | 39        | 626 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 40             | 47             | 118       | 177 |   |
| Impaired loans with related allowance                                                                    |                |                |           |   |   |
| Real estate loans - Home equity                                                                          |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 82             |           | 82        |   | 297 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 44             |           | 44        |   | 247 |
| **Average Recorded Investment**                                                                          |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 44             | 194            | 57        | $ 197 |   |
| **Interest Income Recognized**                                                                           |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 |                |                |      |   |   |
| Other commercial loans                                                                                   |           |           |      |   |   |
| **Unpaid Principal Balance**                                                                             |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 | 13             |           | 13        |   | 20 |
| **Recorded Investment**                                                                                  |           |           |      |   |   |
| Impaired loans with no related allowance                                                                 |                |           |           |   |  |

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