| **Loans and Allowance - Credit Quality of Loan Portfolio by Loan Class (Detail) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2013 | Dec. 31, 2012 |
|-----------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | $ 3,632,409   | $ 2,902,209   |
| Commercial and industrial loans                                                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 761,705       | 622,579       |
| Agricultural production financing and other loans to farmers                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 114,348       | 112,527       |
| Construction                                                                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 177,082       | 98,639        |
| Commercial and farmland                                                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,611,809     | 1,266,682     |
| Residential                                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 616,385       | 473,537       |
| Home Equity                                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 255,223       | 203,406       |
| Consumer                                                                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 69,783        | 75,748        |
| Finance Leases                                                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,545         | 2,590         |
| Other loans                                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 24,529        | 46,501        |
| Commercial Pass                                                                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 2,635,448     | 2,107,317     |
| Commercial Pass | Commercial and industrial loans                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 708,835       | 559,852       |
| Commercial Pass | Agricultural production financing and other loans to farmers                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 114,318       | 112,209       |
| Commercial Pass | Construction                                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 162,976       | 85,728        |
| Commercial Pass | Commercial and farmland                                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,473,714     | 1,148,561     |
| Commercial Pass | Residential                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 143,657       | 145,402       |
| Commercial Pass | Home Equity                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 6,194         | 9,092         |
| Commercial Pass | Finance Leases                                                                                                  |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,420         |          |
| Commercial Pass | Other loans                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 24,334        | 46,473        |
| Commercial Special Mention                                                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 72,407        | 69,815        |
| Commercial Special Mention | Commercial and industrial loans                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 11,332        | 23,678        |
| Commercial Special Mention | Agricultural production financing and other loans to farmers                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             |          | 224           |
| Commercial Special Mention | Construction                                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,132         | 1,384         |
| Commercial Special Mention | Commercial and farmland                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 57,676        | 38,199        |
| Commercial Special Mention | Residential                                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 2,232         | 5,437         |
| Commercial Special Mention | Home Equity                                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 35            | 893           |
| Commercial Substandard                                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 146,254       | 140,553       |
| Commercial Substandard | Commercial and industrial loans                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 41,013        | 34,460        |
| Commercial Substandard | Agricultural production financing and other loans to farmers                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 30            | 94            |
| Commercial Substandard | Construction                                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 12,029        | 11,356        |
| Commercial Substandard | Commercial and farmland                                                                                  |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 80,184        | 79,078        |
| Commercial Substandard | Residential                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 11,494        | 13,880        |
| Commercial Substandard | Home Equity                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,184         | 1,657         |
| Commercial Substandard | Finance Leases                                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 125           |          |
| Commercial Substandard | Other loans                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 195           | 28            |
| Commercial Doubtful                                                                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 661           | 6,064         |
| Commercial Doubtful | Commercial and industrial loans                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 525           | 4,589         |
| Commercial Doubtful | Commercial and farmland                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             |          | 553           |
| Commercial Doubtful | Residential                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 136           | 922           |
| Consumer Performing                                                                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 764,261       | 569,372       |
| Consumer Performing | Residential                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 448,494       | 301,614       |
| Consumer Performing | Home Equity                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 246,101       | 189,721       |
| Consumer Performing | Consumer                                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 69,666        | 75,748        |
| Consumer Performing | Finance Leases                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             |          | 2,289         |
| Consumer Non Performing                                                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 13,378        | 9,088         |
| Consumer Non Performing | Construction                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 945           | 171           |
| Consumer Non Performing | Commercial and farmland                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 235           | 291           |
| Consumer Non Performing | Residential                                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 10,372        | 6,282         |
| Consumer Non Performing | Home Equity                                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 1,709         | 2,043         |
| Consumer Non Performing | Consumer                                                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             | 117           |          |
| Consumer Non Performing | Finance Leases                                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                        |          |          |
| Loans                                                                                                                             |          | $ 301         |

| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| 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
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522
+ Details**Name:**us-gaap_LoansAndLeasesReceivableGrossCarryingAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |