Loans and Leases - Reserve for Loan and Lease Losses and Recorded Investment in Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 3,096				$ 690
Ending balance: collectively evaluated for impairment	21,739				26,406
Total ending balance	24,835	24,718	24,746	[1]	27,096	30,502	29,870
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	66,804				40,754
Ending balance: collectively evaluated for impairment	1,459,437				1,428,757
Total ending balance	1,526,241		1,481,862	[1]	1,469,511
Commercial, financial and agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	2,210				428
Ending balance: collectively evaluated for impairment	8,306				10,827
Total ending balance	10,516	11,395	11,594		11,255	12,021	11,262
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	14,029				4,232
Ending balance: collectively evaluated for impairment	416,789				471,893
Total ending balance	430,818		468,421		476,125
Real Estate-Commercial and Construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	111				262
Ending balance: collectively evaluated for impairment	8,309				9,977
Total ending balance	8,420	8,662	7,507		10,239	12,316	13,317
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	50,242				35,976
Ending balance: collectively evaluated for impairment	630,635				575,012
Total ending balance	680,877				610,988
Real estate-residential secured for business purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	775
Ending balance: collectively evaluated for impairment	456				684
Total ending balance	1,231	586	639		684	834	823
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	1,776				175
Ending balance: collectively evaluated for impairment	33,897				32,645
Total ending balance	35,673		35,179		32,820
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	1,202				946
Total ending balance	1,202	1,084	980		946	884	735
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	720				323
Ending balance: collectively evaluated for impairment	233,181				230,067
Total ending balance	233,901				230,390
Loans to individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	706				606
Total ending balance	706	693	679		606	719	730
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	37				48
Ending balance: collectively evaluated for impairment	42,174				42,578
Total ending balance	42,211		43,780		42,626
Lease financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	1,268				1,184
Total ending balance	1,268	1,212	1,326		1,184	1,161	1,344
Loans and leases held for investment:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	102,761				76,562
Total ending balance	102,761		83,857		76,562
Unallocated [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment
Ending balance: collectively evaluated for impairment	1,492				2,182
Total ending balance	$ 1,492	$ 1,086	$ 2,021		$ 2,182	$ 2,567	$ 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.