| **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                                                             | $ 164,599      |           | $ 164,599 |   | $ 189,779 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 11,848         |           | 11,848    |   | 6,121 |
| Unpaid Principal Balance                                                                                                        | 176,447        |           | 176,447   |   | 195,900 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 103,561        |           | 103,561   |   | 114,253 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 8,650          |           | 8,650     |   | 5,502 |
| Recorded Investment                                                                                                             | 112,211        |           | 112,211   |   | 119,755 |
| Impaired loans with related allowance - Related Allowance                                                                       | 1,708          |           | 1,708     |   | 1,583 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 104,349        | 48,213         | 106,011   | 49,082 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 8,712          | 15,885         | 8,794     | 16,456 |   |
| Average Recorded Investment                                                                                                     | 113,061        | 64,098         | 114,805   | 65,538 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 1,199          | 454            | 2,425     | 904 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 15             | 3              | 30        | 5 |   |
| Interest Income Recognized                                                                                                      | 1,214          | 457            | 2,455     | 909 |   |
| Commercial and industrial loans                                                                                                 |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 29,755         |           | 29,755    |   | 35,066 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 5,107          |           | 5,107     |   | 1,390 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 11,978         |           | 11,978    |   | 16,371 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 3,573          |           | 3,573     |   | 1,216 |
| Impaired loans with related allowance - Related Allowance                                                                       | 942            |           | 942       |   | 683 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 12,060         | 5,864          | 12,872    | 6,138 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 3,575          | 5,669          | 3,590     | 6,138 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 84             | 35             | 185       | 69 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 10             | 3              | 20        | 5 |   |
| Agricultural production financing and other loans to farmers                                                                    |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 29             |           | 29        |   | 32 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 26             |           | 26        |   | 30 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 27             | 33             | 28        | 33 |   |
| Real estate loans - Construction                                                                                                |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 15,119         |           | 15,119    |   | 16,109 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 10,235         |           | 10,235    |   | 10,625 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 10,331         | 3,060          | 10,412    | 3,070 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             |           | 599            |      | 599 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 114            | 19             | 227       | 38 |   |
| Real estate loans - Commercial and farm land                                                                                    |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 109,955        |           | 109,955   |   | 128,073 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 6,741          |           | 6,741     |   | 4,657 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 77,211         |           | 77,211    |   | 83,033 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 5,077          |           | 5,077     |   | 4,215 |
| Impaired loans with related allowance - Related Allowance                                                                       | 766            |           | 766       |   | 894 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 77,716         | 32,932         | 78,288    | 33,192 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 5,137          | 9,227          | 5,204     | 9,323 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 970            | 382            | 1,956     | 760 |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 5              |           | 10        |   |   |
| Real estate loans - Residential                                                                                                 |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 6,317          |           | 6,317     |   | 6,746 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                |           |           |      |   | 74 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 3,915          |           | 3,915     |   | 3,910 |
| Impaired loans with related allowance - Recorded Investment                                                                     |           |           |      |   | 71 |
| Impaired loans with related allowance - Related Allowance                                                                       |           |           |      |   | 6 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 4,017          | 6,067          | 4,212     | 6,372 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             |           | 238            |      | 240 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 31             | 18             | 57        | 37 |   |
| Real estate loans - Home equity                                                                                                 |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 3,389          |           | 3,389     |   | 3,299 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 196            |           | 196       |   | 112 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 198            | 226            | 199       | 245 |   |
| Other loans                                                                                                                     |           |           |      |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |           |      |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 35             |           | 35        |   | 454 |
| Impaired loans with no related allowance - Recorded Investment                                                                  |           |           |      |   | 172 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          |           | 31             |      | 32 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             |           | $ 152          |      | $ 156 |   |

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