Loans and Leases - Reserve for loan and lease losses and recorded investment in loans and leases (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 230				$ 432
Ending balance: collectively evaluated for impairment	24,488				30,070
Total ending balance	24,718	25,222	24,746	[1]	30,502	30,597	29,870
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	38,554				43,730
Ending balance: collectively evaluated for impairment	1,461,439				1,421,719
Total ending balance	1,499,993		1,481,862	[1]	1,465,449
Commercial, financial and agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	230				432
Ending balance: collectively evaluated for impairment	11,165				11,589
Total ending balance	11,395	11,883	11,594		12,021	11,701	11,262
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	3,146				5,647
Ending balance: collectively evaluated for impairment	436,761				492,308
Total ending balance	439,907		468,421		497,955
Real estate-commercial and construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	8,662				12,316
Total ending balance	8,662	8,032	7,507		12,316	13,352	13,317
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	34,471				37,545
Ending balance: collectively evaluated for impairment	629,956				559,647
Total ending balance	664,427				597,192
Real estate-residential secured for business purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	586				834
Total ending balance	586	570	639		834	948	823
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	169				177
Ending balance: collectively evaluated for impairment	32,160				31,920
Total ending balance	32,329		35,179		32,097
Real estate-residential and home equity secured for personal purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	1,084				884
Total ending balance	1,084	792	980		884	732	735
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	730				312
Ending balance: collectively evaluated for impairment	227,381				218,601
Total ending balance	228,111				218,913
Loans to individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	693				719
Total ending balance	693	628	679		719	704	730
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	38				49
Ending balance: collectively evaluated for impairment	43,560				43,988
Total ending balance	43,598		43,780		44,037
Lease financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	1,212				1,161
Total ending balance	1,212	1,358	1,326		1,161	1,160	1,344
Loans and leases held for investment:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	91,621				75,255
Total ending balance	91,621		83,857		75,255
Unallocated [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	1,086				2,567
Total ending balance	$ 1,086	$ 1,959	$ 2,021		$ 2,567	$ 2,000	$ 1,659

[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.