Loans and Leases - Summary of Major Loan and Lease Categories (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	$ 3,081,287	$ 2,390,832
Total Loans and Leases Held for Investment, Acquired	538,780	895,054
Total Loans and Leases Held for Investment	3,620,067	3,285,886
Unearned Lease Income, Originated	(14,243)	(15,970)
Unearned Lease Income, Acquired	0	0
Unearned lease income, included in the above table	(14,243)	(15,970)
Net deferred costs, Originated	4,669	4,503
Net deferred costs, Acquired	0	0
Net deferred costs, included in the above table	4,669	4,503
Overdraft Deposits, Originated	222	84
Overdraft Deposits, Acquired	0	0
Overdraft Deposits	222	84
Commercial, Financial and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	833,100	663,221
Total Loans and Leases Held for Investment, Acquired	63,111	160,045
Total Loans and Leases Held for Investment	896,211	823,266
Real Estate-Commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	1,235,681	909,581
Total Loans and Leases Held for Investment, Acquired	306,460	465,368
Total Loans and Leases Held for Investment	1,542,141	1,374,949
Real Estate-Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	171,244	142,891
Total Loans and Leases Held for Investment, Acquired	4,592	31,953
Total Loans and Leases Held for Investment	175,836	174,844
Real Estate-Residential Secured for Business Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	250,800	151,931
Total Loans and Leases Held for Investment, Acquired	91,167	142,137
Total Loans and Leases Held for Investment	341,967	294,068
Real Estate-Residential Secured for Personal Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	260,654	210,377
Total Loans and Leases Held for Investment, Acquired	60,920	80,431
Total Loans and Leases Held for Investment	321,574	290,808
Real Estate-Home Equity Secured for Personal Purpose [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	171,884	147,982
Total Loans and Leases Held for Investment, Acquired	12,386	14,857
Total Loans and Leases Held for Investment	184,270	162,839
Loans to Individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	28,156	30,110
Total Loans and Leases Held for Investment, Acquired	144	263
Total Loans and Leases Held for Investment	28,300	30,373
Lease Financings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment, Originated	129,768	134,739
Total Loans and Leases Held for Investment, Acquired	0	0
Total Loans and Leases Held for Investment	129,768	134,739
Real Estate-Commercial and Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases Held for Investment	$ 1,717,977	$ 1,549,793