| **Loans and Allowance - Composition of Loan Portfolio by Loan Class (Details) (USD $)In Thousands, unless otherwise specified** | Sep. 30, 2013 | Jun. 30, 2013 | Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Dec. 31, 2011 |
|---------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|---------------|---------------|
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | $ 2,925,457   |          | $ 2,902,209   |          |          |          |
| Allowance for loan losses                                                                                                       | (66,224)      | (68,202)      | (69,366)      | (69,493)      | (70,143)      | (70,898)      |
| Total Loans                                                                                                                     | 2,859,233     |          | 2,832,843     |          |          |          |
| Commercial and industrial loans                                                                                                 |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 652,356       |          | 622,579       |          |          |          |
| Agriculture production financing and other loans to farmers                                                                     |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 98,489        |          | 112,527       |          |          |          |
| Real estate loans - Construction                                                                                                |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 149,875       |          | 98,639        |          |          |          |
| Real estate loans - Commercial and farm land                                                                                    |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 1,264,180     |          | 1,266,682     |          |          |          |
| Real estate loans - Residential                                                                                                 |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 452,277       |          | 473,537       |          |          |          |
| Allowance for loan losses                                                                                                       | (14,706)      | (15,113)      | (14,157)      | (13,127)      | (14,788)      | (12,343)      |
| Real estate loans - Home equity                                                                                                 |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 206,816       |          | 203,406       |          |          |          |
| Individuals' loans for household and other personal expenditures                                                                |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 70,380        |          | 75,748        |          |          |          |
| Allowance for loan losses                                                                                                       | (2,803)       | (2,885)       | (2,593)       | (2,629)       | (2,431)       | (2,902)       |
| Lease financing receivables, net of unearned income                                                                             |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | 1,815         |          | 2,590         |          |          |          |
| Allowance for loan losses                                                                                                       | (56)          | (36)          |     |     |     | (3)           |
| Other Loans                                                                                                                     |          |          |          |          |          |          |
| **Loans:**                                                                                                                      |          |          |          |          |          |          |
| Loans                                                                                                                           | $ 29,269      |          | $ 46,501      |          |          |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.
+ References
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