| **Loans and Allowance for Credit Losses - Allowance for Credit Losses (Detail) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended |
|----------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | $ 67,187        | $ 61,234 | $ 71,229 |
| Charge-offs                                                                                                                      | (35,178)        | (16,969) | (68,293) |
| Recoveries                                                                                                                       | 2,989           | 2,378 | 2,482 |
| Provision for credit losses                                                                                                      | 19,227          | 20,544 | 55,816 |
| Ending Balance                                                                                                                   | 54,225          | 67,187 | 61,234 |
| Ending balance: individually evaluated for impaired                                                                              | 8,824           | 17,778 | 13,236 |
| Ending balance: collectively evaluated for impaired                                                                              | 45,401          | 49,409 | 47,998 |
| Ending balance                                                                                                                   | 4,283,833       | 4,204,704 | 4,043,643 |
| Ending balance: individually evaluated for impaired                                                                              | 52,595          | 100,187 | 94,744 |
| Ending balance: collectively evaluated for impaired                                                                              | 4,231,238       | 4,104,517 | 3,948,899 |
| Commercial, financial, agricultural and other [Member]                                                                           |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 19,852          | 18,200 | 21,700 |
| Charge-offs                                                                                                                      | (18,399)        | (5,207) | (7,114) |
| Recoveries                                                                                                                       | 455             | 443 | 473 |
| Provision for credit losses                                                                                                      | 20,755          | 6,416 | 3,141 |
| Ending Balance                                                                                                                   | 22,663          | 19,852 | 18,200 |
| Ending balance: individually evaluated for impaired                                                                              | 7,364           | 10,331 | 9,069 |
| Ending balance: collectively evaluated for impaired                                                                              | 15,299          | 9,521 | 9,131 |
| Ending balance                                                                                                                   | 1,021,056       | 1,019,822 | 996,739 |
| Ending balance: individually evaluated for impaired                                                                              | 27,251          | 33,443 | 37,639 |
| Ending balance: collectively evaluated for impaired                                                                              | 993,805         | 986,379 | 959,100 |
| Real estate construction [Member]                                                                                                |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 8,928           | 6,756 | 18,002 |
| Charge-offs                                                                                                                      | (773)           | (3,601) | (28,886) |
| Recoveries                                                                                                                       | 501             | 582 | 955 |
| Provision for credit losses                                                                                                      | (2,056)         | 5,191 | 16,685 |
| Ending Balance                                                                                                                   | 6,600           | 8,928 | 6,756 |
| Ending balance: individually evaluated for impaired                                                                              | 94              | 300 | 2,960 |
| Ending balance: collectively evaluated for impaired                                                                              | 6,506           | 8,628 | 3,796 |
| Ending balance                                                                                                                   | 93,289          | 87,438 | 76,564 |
| Ending balance: individually evaluated for impaired                                                                              | 3,844           | 11,177 | 14,667 |
| Ending balance: collectively evaluated for impaired                                                                              | 89,445          | 76,261 | 61,897 |
| Residential real estate [Member]                                                                                                 |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 5,908           | 8,237 | 5,454 |
| Charge-offs                                                                                                                      | (1,814)         | (3,828) | (4,107) |
| Recoveries                                                                                                                       | 1,264           | 422 | 132 |
| Provision for credit losses                                                                                                      | 2,369           | 1,077 | 6,758 |
| Ending Balance                                                                                                                   | 7,727           | 5,908 | 8,237 |
| Ending balance: individually evaluated for impaired                                                                              | 1,282           | 780 | 93 |
| Ending balance: collectively evaluated for impaired                                                                              | 6,445           | 5,128 | 8,144 |
| Ending balance                                                                                                                   | 1,262,718       | 1,241,565 | 1,137,059 |
| Ending balance: individually evaluated for impaired                                                                              | 9,349           | 6,444 | 2,606 |
| Ending balance: collectively evaluated for impaired                                                                              | 1,253,369       | 1,235,121 | 1,134,453 |
| Commercial real estate [Member]                                                                                                  |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 22,441          | 18,961 | 16,913 |
| Charge-offs                                                                                                                      | (10,513)        | (851) | (24,861) |
| Recoveries                                                                                                                       | 136             | 410 | 349 |
| Provision for credit losses                                                                                                      | (286)           | 3,921 | 26,560 |
| Ending Balance                                                                                                                   | 11,778          | 22,441 | 18,961 |
| Ending balance: individually evaluated for impaired                                                                              | 84              | 6,367 | 1,114 |
| Ending balance: collectively evaluated for impaired                                                                              | 11,694          | 16,074 | 17,847 |
| Ending balance                                                                                                                   | 1,296,472       | 1,273,661 | 1,267,432 |
| Ending balance: individually evaluated for impaired                                                                              | 12,151          | 49,123 | 39,832 |
| Ending balance: collectively evaluated for impaired                                                                              | 1,284,321       | 1,224,538 | 1,227,600 |
| Loans to individuals [Member]                                                                                                    |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 4,132           | 4,244 | 4,215 |
| Charge-offs                                                                                                                      | (3,679)         | (3,482) | (3,325) |
| Recoveries                                                                                                                       | 633             | 521 | 573 |
| Provision for credit losses                                                                                                      | 4,371           | 2,849 | 2,781 |
| Ending Balance                                                                                                                   | 5,457           | 4,132 | 4,244 |
| Ending balance: individually evaluated for impaired                                                                              | 0               | 0 | 0 |
| Ending balance: collectively evaluated for impaired                                                                              | 5,457           | 4,132 | 4,244 |
| Ending balance                                                                                                                   | 610,298         | 582,218 | 565,849 |
| Ending balance: individually evaluated for impaired                                                                              | 0               | 0 | 0 |
| Ending balance: collectively evaluated for impaired                                                                              | 610,298         | 582,218 | 565,849 |
| Unallocated [Member]                                                                                                             |            |   |   |
| **Financing Receivable, Allowance for Credit Losses [Roll Forward]**                                                             |            |   |   |
| Beginning Balance                                                                                                                | 5,926           | 4,836 | 4,945 |
| Charge-offs                                                                                                                      | 0               | 0 | 0 |
| Recoveries                                                                                                                       | 0               | 0 | 0 |
| Provision for credit losses                                                                                                      | (5,926)         | 1,090 | (109) |
| Ending Balance                                                                                                                   | 0               | 5,926 | 4,836 |
| Ending balance: individually evaluated for impaired                                                                              | 0               | 0 | 0 |
| Ending balance: collectively evaluated for impaired                                                                              | $ 0             | $ 5,926 | $ 4,836 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A valuation allowance for financing receivables that are expected to be uncollectible.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of recovery of financing receivables doubtful of collection that were previously charged off.
+ References
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| X                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of direct write-downs of financing receivables charged against the allowance.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were collectively evaluated for impairment.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables that were individually evaluated for impairment.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before allowance and after 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.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5074-111524Reference 2: 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=6375948&loc=d3e4428-111522Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Statement of Position (SOP) -Number 01-6 -Paragraph 13 -Subparagraph e -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher OTS -Name Federal Regulation (FR) -Number Title 12 -Section 563c.102 -Paragraph 8 -Subparagraph e -Chapter V -Subsection I -LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy.  It will be removed from future versions of this taxonomy.Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-DEP -Paragraph 116 -IssueDate 2006-05-01 -Chapter 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Provision charged for the period based on estimated losses to be realized from loan and lease transactions.
+ References
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