Loans and Leases - Age Analysis of Past Due Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012		Sep. 30, 2012
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	$ 8,782	$ 14,266
60-89 Days Past Due	4,416	1,024
Greater Than 90 Days Past Due	17,660	20,728
Total Past Due	30,858	36,018
Current	1,495,383	1,445,844
Total ending balance	1,526,241	1,481,862	[1]	1,469,511
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	1,954	441
Commercial, financial and agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	4,169	586
60-89 Days Past Due	972	313
Greater Than 90 Days Past Due	1,047	754
Total Past Due	6,188	1,653
Current	424,630	466,768
Total ending balance	430,818	468,421		476,125
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	300
Real estate-commercial real estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	651	8,266
60-89 Days Past Due	1,364
Greater Than 90 Days Past Due	6,405	5,894
Total Past Due	8,420	14,160
Current	597,610	515,962
Total ending balance	606,030	530,122
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	641
Real estate-construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due		306
60-89 Days Past Due
Greater Than 90 Days Past Due	8,742	13,150
Total Past Due	8,742	13,456
Current	66,105	77,794
Total ending balance	74,847	91,250
Recorded Investment Greater than 90 Days Past Due and Accruing Interest
Real estate-residential secured for business purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	411	1,663
60-89 Days Past Due	180	69
Greater Than 90 Days Past Due	226	103
Total Past Due	817	1,835
Current	34,856	33,344
Total ending balance	35,673	35,179		32,820
Recorded Investment Greater than 90 Days Past Due and Accruing Interest
Real estate-residential secured for personal purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,122	1,617
60-89 Days Past Due	197	152
Greater Than 90 Days Past Due	619
Total Past Due	1,938	1,769
Current	141,436	144,757
Total ending balance	143,374	146,526
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	619
Real estate-home equity secured for personal purpose [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	341	276
60-89 Days Past Due	76	64
Greater Than 90 Days Past Due	51	54
Total Past Due	468	394
Current	90,059	82,333
Total ending balance	90,527	82,727
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	51	54
Loans to individuals [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	496	551
60-89 Days Past Due	255	153
Greater Than 90 Days Past Due	299	347
Total Past Due	1,050	1,051
Current	41,161	42,729
Total ending balance	42,211	43,780		42,626
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	299	347
Lease financings [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-59 Days Past Due	1,592	1,001
60-89 Days Past Due	1,372	273
Greater Than 90 Days Past Due	271	426
Total Past Due	3,235	1,700
Current	99,526	82,157
Total ending balance	102,761	83,857		76,562
Recorded Investment Greater than 90 Days Past Due and Accruing Interest	$ 44	$ 40

[1] Note: The consolidated balance sheet at December 31, 2012 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U. S. generally accepted accounting principles for complete financial statements. See accompanying notes to the unaudited consolidated financial statements.