| **Loans and Allowance - Composition of Impaired Loans by Loan Class (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended |        |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|--------|
||
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | $ 176,090      |   | $ 189,779 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 9,153          |   | 6,121 |
| Unpaid Principal Balance                                                                                                        | 185,243        |   | 195,900 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 111,706        |   | 114,253 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 6,126          |   | 5,502 |
| Recorded Investment                                                                                                             | 117,832        |   | 119,755 |
| Impaired loans with related allowance - Related Allowance                                                                       | 1,794          |   | 1,583 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 112,759        | 56,963 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 6,150          | 13,857 |   |
| Average Recorded Investment                                                                                                     | 118,909        | 70,820 |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 300            | 470    |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 4              | 3      |   |
| Interest Income Recognized                                                                                                      | 304            | 473    |   |
| Commercial and industrial loans                                                                                                 |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 35,562         |   | 35,066 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 1,789          |   | 1,390 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 16,302         |   | 16,371 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 1,741          |   | 1,216 |
| Impaired loans with related allowance - Related Allowance                                                                       | 902            |   | 683 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 16,377         | 8,043  |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 1,752          | 5,124  |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 21             | 44     |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 3              | 3      |   |
| Agricultural production financing and other loans to farmers                                                                    |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 31             |   | 32 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 28             |   | 30 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 29             | 86     |   |
| Real estate loans - Construction                                                                                                |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 15,184         |   | 16,109 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                |      |   |   |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 10,327         |   | 10,625 |
| Impaired loans with related allowance - Recorded Investment                                                                     |      |   |   |
| Impaired loans with related allowance - Related Allowance                                                                       |      |   |   |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 10,440         | 3,936  |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             |           | 915    |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 28             | 19     |   |
| Real estate loans - Commercial and farm land                                                                                    |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 115,745        |   | 128,073 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                | 7,364          |   | 4,657 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 80,957         |   | 83,033 |
| Impaired loans with related allowance - Recorded Investment                                                                     | 4,385          |   | 4,215 |
| Impaired loans with related allowance - Related Allowance                                                                       | 892            |   | 894 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 81,617         | 39,228 |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             | 4,398          | 5,428  |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 243            | 382    |   |
| Impaired loans with related allowance - Interest Income Recognized                                                              | 1              |   |   |
| Real estate loans - Residential                                                                                                 |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 6,196          |   | 6,746 |
| Impaired loans with related allowance - Unpaid Principal Balance                                                                |      |   | 74 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 3,948          |   | 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                                                          | 4,146          | 4,737  |   |
| Impaired loans with related allowance - Average Recorded Investment                                                             |           | 2,390  |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           | 8              | 22     |   |
| Real estate loans - Home equity                                                                                                 |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 3,332          |   | 3,299 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 142            |   | 112 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | 144            | 923    |   |
| Impaired loans with no related allowance - Interest Income Recognized                                                           |           | 3      |   |
| Other loans                                                                                                                     |           |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                 |           |   |   |
| Impaired loans with no related allowance - Unpaid Principal Balance                                                             | 40             |   | 454 |
| Impaired loans with no related allowance - Recorded Investment                                                                  | 2              |   | 172 |
| Impaired loans with no related allowance - Average Recorded Investment                                                          | $ 6            | $ 10   |   |

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