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)