| **Loans and Allowance - Composition of Loan Portfolio by Loan Class (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 |
|--------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|---------------|
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | $ 3,632,409   | $ 2,902,209   |          |          |
| Allowance for loan losses                                                                                                      | (67,870)      | (69,366)      | (70,898)      | (82,977)      |
| Net loans                                                                                                                      | 3,564,539     | 2,832,843     |          |          |
| Commercial and industrial loans                                                                                                |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 761,705       | 622,579       |          |          |
| Agricultural production financing and other loans to farmers                                                                   |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 114,348       | 112,527       |          |          |
| Construction                                                                                                                   |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 177,082       | 98,639        |          |          |
| Commercial and farmland                                                                                                        |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 1,611,809     | 1,266,682     |          |          |
| Residential                                                                                                                    |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 616,385       | 473,537       |          |          |
| Allowance for loan losses                                                                                                      | (15,077)      | (14,157)      | (12,343)      | (10,408)      |
| Home Equity                                                                                                                    |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 255,223       | 203,406       |          |          |
| Individuals' loans for household and other personal expenditures                                                               |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 69,783        | 75,748        |          |          |
| Allowance for loan losses                                                                                                      | (2,515)       | (2,593)       | (2,902)       | (3,622)       |
| Lease financing receivables, net of unearned income                                                                            |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | 1,545         | 2,590         |          |          |
| Allowance for loan losses                                                                                                      |     |     | (3)           | (98)          |
| Other loans                                                                                                                    |          |          |          |          |
| **Loans:**                                                                                                                     |          |          |          |          |
| Loans                                                                                                                          | $ 24,529      | $ 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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| X                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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