Loans and Leases - Reserve for Loan and Lease Losses and Recorded Investment in Loans and Leases (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 998	$ 2,963
Ending balance: collectively evaluated for impairment	19,664	21,531
Total ending balance	20,662	24,494	24,746	29,870
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	56,191	58,333
Ending balance: collectively evaluated for impairment	1,570,434	1,483,151
Total Loans and Leases Held for Investment	1,626,625	1,541,484
Commercial, Financial and Agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	920	2,398
Ending balance: collectively evaluated for impairment	6,000	7,391
Total ending balance	6,920	9,789	11,594	11,262
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	16,561	14,105
Ending balance: collectively evaluated for impairment	441,266	408,711
Total Loans and Leases Held for Investment	457,827	422,816
Real Estate-Commercial and Construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	78	0
Ending balance: collectively evaluated for impairment	8,865	8,780
Total ending balance	8,943	8,780	7,507	13,317
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	35,926	41,240
Ending balance: collectively evaluated for impairment	672,439	649,606
Total Loans and Leases Held for Investment	708,365	690,846
Real Estate-Residential Secured for Business Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0	501
Ending balance: collectively evaluated for impairment	763	561
Total ending balance	763	1,062	639	823
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	3,008	1,774
Ending balance: collectively evaluated for impairment	33,924	35,545
Total Loans and Leases Held for Investment	36,932	37,319
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0	64
Ending balance: collectively evaluated for impairment	1,124	1,220
Total ending balance	1,124	1,284	980	735
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	696	1,178
Ending balance: collectively evaluated for impairment	274,404	243,331
Total Loans and Leases Held for Investment	275,100	244,509
Loans to Individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	360	694
Total ending balance	360	694	679	730
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0	36
Ending balance: collectively evaluated for impairment	29,941	39,964
Total Loans and Leases Held for Investment	29,941	40,000
Lease Financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	985	1,285
Total ending balance	985	1,285	1,326	1,344
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0	0
Ending balance: collectively evaluated for impairment	118,460	105,994
Total Loans and Leases Held for Investment	118,460	105,994
Unallocated [Member]
Reserve for loan and lease losses:
Ending balance: collectively evaluated for impairment	1,567	1,600
Total ending balance	$ 1,567	$ 1,600	$ 2,021	$ 1,659