| **Loans and Allowance for Credit Losses - Outstanding Balances of Loan (Detail) - USD ($) $ in Thousands** | Jun. 30, 2022 | Dec. 31, 2021 | Jun. 30, 2021 |
|------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | $ (7,119,754) | $ (6,839,230) | $ (6,740,535) |
| Commercial, financial, agricultural and other [Member]                                                     |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,170,583)   | (1,173,452)   | (1,374,177)   |
| Commercial, financial, agricultural and other [Member] | Time and Demand Loans                             |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,031,930)   | (1,159,524)   | (1,360,065)   |
| Commercial, financial, agricultural and other [Member] | Commercial Credit Cards                           |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (16,329)      | (13,928)      | (14,112)      |
| Commercial, financial, agricultural and other [Member] | Equipment Finance                                 |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (21,062)      |          |          |
| Commercial, financial, agricultural and other [Member] | Time and Demand Loans Other                       |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (101,262)     |          |          |
| Real estate construction [Member]                                                                          |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (392,992)     | (494,456)     | (414,816)     |
| Real estate construction [Member] | Construction Other                                                     |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (292,400)     |          |          |
| Real estate construction [Member] | Construction Residential                                               |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (100,592)     |          |          |
| Residential real estate [Member]                                                                           |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (2,100,201)   | (1,920,250)   | (1,828,783)   |
| Residential real estate [Member] | Senior Lien                                                             |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,459,861)   | (1,299,534)   | (1,218,300)   |
| Residential real estate [Member] | Junior Lien                                                             |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (640,340)     | (620,716)     | (610,483)     |
| Commercial Real Estate [Member]                                                                            |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (2,319,094)   | (2,251,097)   | (2,205,758)   |
| Commercial Real Estate [Member] | Multifamily                                                              |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (360,335)     | (385,432)     | (385,905)     |
| Commercial Real Estate [Member] | Nonowner Occupied Commercial Real Estate                                 |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,510,804)   | (1,465,247)   | (1,429,192)   |
| Commercial Real Estate [Member] | Owner Occupied Commercial Real Estate                                    |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (447,955)     | (400,418)     | (390,661)     |
| Loans to individuals [Member]                                                                              |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,136,884)   | (999,975)     | (917,001)     |
| Loans to individuals [Member] | Automobiles                                                                |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (1,047,104)   | (901,280)     | (829,150)     |
| Loans to individuals [Member] | Consumer Credit Cards                                                      |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | (8,717)       | (11,151)      | (10,834)      |
| Loans to individuals [Member] | Other Consumer Loans                                                       |          |          |          |
| **Accounts, Notes, Loans and Financing Receivable [Line Items]**                                           |          |          |          |
| Loans and Leases Receivable, Net of Deferred Income                                                        | $ (81,063)    | $ (87,544)    | $ (77,017)    |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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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
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