| **Loans and Allowance for Credit Losses - Recorded Investment and Unpaid Principal Balance for Impaired Loans with Associated Allowance (Detail) (USD $)In Thousands, unless otherwise specified** | 12 Months Ended |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | $ 59,383        | $ 107,555 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 66,307          | 139,687 |   |
| Related Allowance                                                                                                                                                                                  | 8,824           | 17,778 |   |
| Average Recorded Investment                                                                                                                                                                        | 78,175          | 87,979 | 139,922 |
| Interest Income Recognized                                                                                                                                                                         | 679             | 369 | 1,393 |
| Commercial, financial, agricultural and other with no related allowance recorded [Member]                                                                                                          |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 6,752           | 8,080 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 7,649           | 8,983 |   |
| Average Recorded Investment                                                                                                                                                                        | 14,454          | 9,217 | 3,887 |
| Interest Income Recognized                                                                                                                                                                         | 73              | 173 | 20 |
| Real estate construction with no related allowance recorded [Member]                                                                                                                               |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 3,486           | 8,491 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 6,664           | 35,555 |   |
| Average Recorded Investment                                                                                                                                                                        | 5,923           | 11,912 | 23,254 |
| Interest Income Recognized                                                                                                                                                                         | 47              | 0 | 10 |
| Residential real estate with no related allowance recorded [Member]                                                                                                                                |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 9,333           | 7,928 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 9,952           | 8,401 |   |
| Average Recorded Investment                                                                                                                                                                        | 9,280           | 8,114 | 2,702 |
| Interest Income Recognized                                                                                                                                                                         | 211             | 72 | 9 |
| Commercial real estate with no related allowance recorded [Member]                                                                                                                                 |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 13,606          | 33,259 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 14,719          | 35,401 |   |
| Average Recorded Investment                                                                                                                                                                        | 27,881          | 28,574 | 35,817 |
| Interest Income Recognized                                                                                                                                                                         | 250             | 66 | 799 |
| Loans to individuals with no related allowance recorded [Member]                                                                                                                                   |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 289             | 256 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 307             | 256 |   |
| Average Recorded Investment                                                                                                                                                                        | 255             | 103 | 10 |
| Interest Income Recognized                                                                                                                                                                         | 3               | 2 | 0 |
| Subtotal with no related allowance recorded [Member]                                                                                                                                               |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 33,466          | 58,014 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 39,291          | 88,596 |   |
| Average Recorded Investment                                                                                                                                                                        | 57,793          | 57,920 | 65,670 |
| Interest Income Recognized                                                                                                                                                                         | 584             | 313 | 838 |
| Commercial, financial, agricultural and other With an allowance recorded [Member]                                                                                                                  |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 21,482          | 26,532 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 22,082          | 27,412 |   |
| Related Allowance                                                                                                                                                                                  | 7,364           | 10,331 |   |
| Average Recorded Investment                                                                                                                                                                        | 16,479          | 21,979 | 30,456 |
| Interest Income Recognized                                                                                                                                                                         | 64              | 9 | 152 |
| Real estate construction with an allowance recorded [Member]                                                                                                                                       |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 414             | 2,756 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 737             | 3,087 |   |
| Related Allowance                                                                                                                                                                                  | 94              | 300 |   |
| Average Recorded Investment                                                                                                                                                                        | 515             | 1,457 | 14,465 |
| Interest Income Recognized                                                                                                                                                                         | 0               | 0 | 0 |
| Residential real estate With an allowance recorded [Member]                                                                                                                                        |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 3,533           | 2,695 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 3,585           | 2,696 |   |
| Related Allowance                                                                                                                                                                                  | 1,282           | 780 |   |
| Average Recorded Investment                                                                                                                                                                        | 3,200           | 1,599 | 615 |
| Interest Income Recognized                                                                                                                                                                         | 31              | 15 | 7 |
| Commercial real estate With an allowance recorded [Member]                                                                                                                                         |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 488             | 17,558 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 612             | 17,896 |   |
| Related Allowance                                                                                                                                                                                  | 84              | 6,367 |   |
| Average Recorded Investment                                                                                                                                                                        | 188             | 5,024 | 28,716 |
| Interest Income Recognized                                                                                                                                                                         | 0               | 32 | 396 |
| Loans to individuals With an allowance recorded [Member]                                                                                                                                           |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 0               | 0 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 0               | 0 |   |
| Related Allowance                                                                                                                                                                                  | 0               | 0 |   |
| Average Recorded Investment                                                                                                                                                                        | 0               | 0 | 0 |
| Interest Income Recognized                                                                                                                                                                         | 0               | 0 | 0 |
| Subtotal With an allowance recorded [Member]                                                                                                                                                       |            |   |   |
| **Financing Receivable, Impaired [Line Items]**                                                                                                                                                    |            |   |   |
| Recorded Investment                                                                                                                                                                                | 25,917          | 49,541 |   |
| Unpaid Principal Balance                                                                                                                                                                           | 27,016          | 51,091 |   |
| Related Allowance                                                                                                                                                                                  | 8,824           | 17,778 |   |
| Average Recorded Investment                                                                                                                                                                        | 20,382          | 30,059 | 74,252 |
| Interest Income Recognized                                                                                                                                                                         | $ 95            | $ 56 | $ 555 |

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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.
+ References
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| - Definition
Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
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| - Definition
Amount of allowance for credit losses related to recorded investment.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.
+ References
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