Loans and Leases - Age Analysis of Past Due Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 3,405	$ 4,896
60-89 Days Past Due	3,196	2,205
90 Days or more Past Due	11,043	18,164
Total Past Due	17,644	25,265
Current	1,608,981	1,516,219
Total Loans and Leases Held for Investment	1,626,625	1,541,484
Recorded Investment 90 Days or more Past Due and Accruing Interest	451	413
Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	145	386
60-89 Days Past Due	747	922
90 Days or more Past Due	2,567	2,904
Total Past Due	3,459	4,212
Current	454,368	418,604
Total Loans and Leases Held for Investment	457,827	422,816
Recorded Investment 90 Days or more Past Due and Accruing Interest	0	12
Real Estate-Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	361	148
60-89 Days Past Due	913	262
90 Days or more Past Due	1,163	4,932
Total Past Due	2,437	5,342
Current	626,041	595,011
Total Loans and Leases Held for Investment	628,478	600,353
Recorded Investment 90 Days or more Past Due and Accruing Interest	0	0
Real Estate-Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	0	0
60-89 Days Past Due	405	0
90 Days or more Past Due	5,525	8,742
Total Past Due	5,930	8,742
Current	73,957	81,751
Total Loans and Leases Held for Investment	79,887	90,493
Recorded Investment 90 Days or more Past Due and Accruing Interest	0	0
Real Estate-Residential Secured for Business Purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	167	87
60-89 Days Past Due	56	276
90 Days or more Past Due	713	161
Total Past Due	936	524
Current	35,996	36,795
Total Loans and Leases Held for Investment	36,932	37,319
Recorded Investment 90 Days or more Past Due and Accruing Interest	0	0
Real Estate-Residential Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	409	1,370
60-89 Days Past Due	604	0
90 Days or more Past Due	60	617
Total Past Due	1,073	1,987
Current	165,777	147,177
Total Loans and Leases Held for Investment	166,850	149,164
Recorded Investment 90 Days or more Past Due and Accruing Interest	0	0
Real Estate-Home Equity Secured for Personal Purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	348	278
60-89 Days Past Due	0	97
90 Days or more Past Due	215	100
Total Past Due	563	475
Current	107,687	94,870
Total Loans and Leases Held for Investment	108,250	95,345
Recorded Investment 90 Days or more Past Due and Accruing Interest	31	23
Loans to Individuals [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	365	445
60-89 Days Past Due	65	193
90 Days or more Past Due	365	319
Total Past Due	795	957
Current	29,146	39,043
Total Loans and Leases Held for Investment	29,941	40,000
Recorded Investment 90 Days or more Past Due and Accruing Interest	365	319
Lease Financings [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,610	2,182
60-89 Days Past Due	406	455
90 Days or more Past Due	435	389
Total Past Due	2,451	3,026
Current	116,009	102,968
Total Loans and Leases Held for Investment	118,460	105,994
Recorded Investment 90 Days or more Past Due and Accruing Interest	$ 55	$ 59