| **Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended | 6 Months Ended |              |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|--------------|
||
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | $ 78,810       |           | $ 78,810     |   | $ 109,594 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 19,189         |           | 19,189       |   | 12,918 |
| Unpaid Principal Balance                                                                                                        | 97,999         |           | 97,999       |   | 122,512 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 47,524         |           | 47,524       |   | 67,333 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 15,465         |           | 15,465       |   | 11,846 |
| Recorded Investment                                                                                                             | 62,989         |           | 62,989       |   | 79,179 |
| Impaired loans with related allowance - Related Allowance                                                                       | 4,548          |           | 4,548        |   | 4,243 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 48,213         | 67,077         | 49,082       | 70,429 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 15,885         | 18,423         | 16,456       | 18,570 |   |
| Average Recorded Investment                                                                                                     | 64,098         | 85,500         | 65,538       | 88,999 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 454            | 388            | 904          | 700 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 3              | 75             | 5            | 148 |   |
| Interest Income Recognized                                                                                                      | 457            | 463            | 909          | 848 |   |
| Commercial and industrial loans                                                                                                 |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 17,836         |           | 17,836       |   | 28,532 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 7,193          |           | 7,193        |   | 4,415 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 5,556          |           | 5,556        |   | 11,730 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 5,306          |           | 5,306        |   | 4,155 |
| Impaired loans with related allowance - Related Allowance                                                                       | 1,476          |           | 1,476        |   | 1,628 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 5,864          | 11,411         | 6,138        | 12,418 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 5,669          | 6,111          | 6,138        | 6,136 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 35             | 39             | 69           | 64 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 3              | 11             | 5            | 21 |   |
| Agriculture production financing and other loans to farmers                                                                     |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 34             |           | 34           |   |   |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 33             |           | 33           |   |   |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 33             |           | 33           |   |   |
| Real estate loans - Construction                                                                                                |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 4,540          |           | 4,540        |   | 9,787 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 961            |           | 961          |   | 1,202 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 3,053          |           | 3,053        |   | 5,164 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 599            |           | 599          |   | 1,058 |
| Impaired loans with related allowance - Related Allowance                                                                       | 74             |           | 74           |   | 105 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 3,060          | 8,040          | 3,070        | 8,581 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 599            | 1,931          | 599          | 1,936 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 19             | 16             | 38           | 29 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              |           |      |         |    |   |
| Real estate loans - Commercial and farm land                                                                                    |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 44,620         |           | 44,620       |   | 58,173 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 10,249         |           | 10,249       |   | 5,579 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 32,658         |           | 32,658       |   | 43,204 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 9,177          |           | 9,177        |   | 5,182 |
| Impaired loans with related allowance - Related Allowance                                                                       | 2,823          |           | 2,823        |   | 2,460 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 32,932         | 41,084         | 33,192       | 42,615 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 9,227          | 8,369          | 9,323        | 8,505 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 382            | 315            | 760          | 575 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              |      | 45             |    | 89 |   |
| Real estate loans - Residential                                                                                                 |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 8,228          |           | 8,228        |   | 8,820 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 465            |           | 465          |   | 1,722 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 5,968          |           | 5,968        |   | 6,215 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 235            |           | 235          |   | 1,451 |
| Impaired loans with related allowance - Related Allowance                                                                       | 29             |           | 29           |   | 50 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 6,067          | 5,815          | 6,372        | 6,072 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 238            | 2,012          | 240          | 1,993 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 18             | 15             | 37           | 26 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              |      | 19             |    | 38 |   |
| Real estate loans - Home equity                                                                                                 |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 3,412          |           | 3,412        |   | 4,199 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 226            |           | 226          |   | 1,006 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 226            | 570            | 245          | 585 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           |      | 3              |    | 6 |   |
| Individuals' loans for household and other personal expenditures                                                                |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Average Recorded Investment                                                          |           | 139            |         | 139 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           |           |      |         |    |   |
| Other Loans                                                                                                                     |           |           |         |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |         |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 140            |           | 140          |   | 83 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 321            |           | 321          |   |   |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 30             |           | 30           |   | 14 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 148            |           | 148          |   |   |
| Impaired loans with related allowance - Related Allowance                                                                       | 146            |           | 146          |   |   |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 31             | 18             | 32           | 19 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 152            |           | 156          |   |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           |           |      |         |    |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              |      |           |    |   |   |

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