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, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 1,142			$ 3,096
Ending balance: collectively evaluated for impairment	20,620			21,739
Total ending balance	21,762	24,094	24,494	24,835	24,718	24,746
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	59,079			66,804
Ending balance: collectively evaluated for impairment	1,538,657			1,459,437
Total Loans and Leases Held for Investment	1,597,736		1,541,484	1,526,241
Commercial, Financial and Agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	685			2,210
Ending balance: collectively evaluated for impairment	6,930			8,306
Total ending balance	7,615	9,714	9,789	10,516	11,395	11,594
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	18,214			14,029
Ending balance: collectively evaluated for impairment	420,342			416,789
Total Loans and Leases Held for Investment	438,556		422,816	430,818
Real Estate-Commercial and Construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	27			111
Ending balance: collectively evaluated for impairment	9,061			8,309
Total ending balance	9,088	9,263	8,780	8,420	8,662	7,507
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	37,341			50,242
Ending balance: collectively evaluated for impairment	675,817			630,635
Total Loans and Leases Held for Investment	713,158			680,877
Real Estate-Residential Secured for Business Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	430			775
Ending balance: collectively evaluated for impairment	530			456
Total ending balance	960	1,025	1,062	1,231	586	639
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	2,921			1,776
Ending balance: collectively evaluated for impairment	32,446			33,897
Total Loans and Leases Held for Investment	35,367		37,319	35,673
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	1,178			1,202
Total ending balance	1,178	1,248	1,284	1,202	1,084	980
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	603			720
Ending balance: collectively evaluated for impairment	267,956			233,181
Total Loans and Leases Held for Investment	268,559			233,901
Loans to Individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	332			706
Total ending balance	332	405	694	706	693	679
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0			37
Ending balance: collectively evaluated for impairment	30,144			42,174
Total Loans and Leases Held for Investment	30,144		40,000	42,211
Lease Financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	1,115			1,268
Total ending balance	1,115	1,101	1,285	1,268	1,212	1,326
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	111,952			102,761
Total Loans and Leases Held for Investment	111,952		105,994	102,761
Unallocated [Member]
Reserve for loan and lease losses:
Ending balance: collectively evaluated for impairment	1,474			1,492
Total ending balance	$ 1,474	$ 1,338	$ 1,600	$ 1,492	$ 1,086	$ 2,021