| **Loans and Allowance for Credit Losses - Credit Risk Profile by Creditworthiness (Detail) (USD $)In Thousands, unless otherwise specified** | Jun. 30, 2014 | Dec. 31, 2013 |
|----------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | $ 4,334,214   | $ 4,283,833   |
| Pass [Member]                                                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 4,176,844     | 4,121,472     |
| OAEM [Member]                                                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 87,204        | 79,124        |
| Substandard [Member]                                                                                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 65,888        | 83,237        |
| Doubtful [Member]                                                                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 4,278         | 0             |
| Total Non-Pass [Member]                                                                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 157,370       | 162,361       |
| Commercial, financial, agricultural and other [Member]                                                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 1,062,001     | 1,021,056     |
| Commercial, financial, agricultural and other [Member] | Pass [Member]                                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 976,591       | 943,107       |
| Commercial, financial, agricultural and other [Member] | OAEM [Member]                                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 46,934        | 35,429        |
| Commercial, financial, agricultural and other [Member] | Substandard [Member]                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 34,198        | 42,520        |
| Commercial, financial, agricultural and other [Member] | Doubtful [Member]                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 4,278         | 0             |
| Commercial, financial, agricultural and other [Member] | Total Non-Pass [Member]                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 85,410        | 77,949        |
| Real estate construction [Member]                                                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 100,709       | 93,289        |
| Real estate construction [Member] | Pass [Member]                                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 91,732        | 79,679        |
| Real estate construction [Member] | OAEM [Member]                                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 8,310         | 9,710         |
| Real estate construction [Member] | Substandard [Member]                                                                                     |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 667           | 3,900         |
| Real estate construction [Member] | Doubtful [Member]                                                                                        |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 0             | 0             |
| Real estate construction [Member] | Total Non-Pass [Member]                                                                                  |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 8,977         | 13,610        |
| Residential real estate [Member]                                                                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 1,238,791     | 1,262,718     |
| Residential real estate [Member] | Pass [Member]                                                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 1,225,291     | 1,245,422     |
| Residential real estate [Member] | OAEM [Member]                                                                                             |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 3,160         | 5,161         |
| Residential real estate [Member] | Substandard [Member]                                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 10,340        | 12,135        |
| Residential real estate [Member] | Doubtful [Member]                                                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 0             | 0             |
| Residential real estate [Member] | Total Non-Pass [Member]                                                                                   |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 13,500        | 17,296        |
| Commercial Real Estate [Member]                                                                                                              |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 1,306,752     | 1,296,472     |
| Commercial Real Estate [Member] | Pass [Member]                                                                                              |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 1,257,512     | 1,243,170     |
| Commercial Real Estate [Member] | OAEM [Member]                                                                                              |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 28,800        | 28,823        |
| Commercial Real Estate [Member] | Substandard [Member]                                                                                       |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 20,440        | 24,479        |
| Commercial Real Estate [Member] | Doubtful [Member]                                                                                          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 0             | 0             |
| Commercial Real Estate [Member] | Total Non-Pass [Member]                                                                                    |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 49,240        | 53,302        |
| Loans to individuals [Member]                                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 625,961       | 610,298       |
| Loans to individuals [Member] | Pass [Member]                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 625,718       | 610,094       |
| Loans to individuals [Member] | OAEM [Member]                                                                                                |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 0             | 1             |
| Loans to individuals [Member] | Substandard [Member]                                                                                         |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 243           | 203           |
| Loans to individuals [Member] | Doubtful [Member]                                                                                            |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | 0             | 0             |
| Loans to individuals [Member] | Total Non-Pass [Member]                                                                                      |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                                                             |          |          |
| Loans and Leases Receivable, Gross                                                                                                           | $ 243         | $ 204         |

| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**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 |