Loans and Leases - Credit quality indicators (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012		Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	$ 1,499,993	$ 1,481,862	[1]	$ 1,465,449
Commercial, financial and agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	439,907	468,421		497,955
Commercial, financial and agricultural [Member] | Grade:1. Cash secured/2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	851	2,263
Commercial, financial and agricultural [Member] | Grade:3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	6,106	5,227
Commercial, financial and agricultural [Member] | Grade:4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	38,401	40,747
Commercial, financial and agricultural [Member] | Grade:5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	243,168	260,042
Commercial, financial and agricultural [Member] | Grade:6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	105,622	106,436
Commercial, financial and agricultural [Member] | Grade:7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	23,053	31,825
Commercial, financial and agricultural [Member] | Grade:8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	22,706	21,881
Commercial, financial and agricultural [Member] | Grade:9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Commercial, financial and agricultural [Member] | Grade:10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	580,400	530,122
Real estate-commercial real estate [Member] | Grade:1. Cash secured/2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-commercial real estate [Member] | Grade:3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	9,502	9,591
Real estate-commercial real estate [Member] | Grade:4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	21,123	25,837
Real estate-commercial real estate [Member] | Grade:5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	353,806	321,194
Real estate-commercial real estate [Member] | Grade:6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	140,034	110,476
Real estate-commercial real estate [Member] | Grade:7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	13,415	16,187
Real estate-commercial real estate [Member] | Grade:8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	42,520	45,844
Real estate-commercial real estate [Member] | Grade:9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment		993
Real estate-commercial real estate [Member] | Grade:10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	84,027	91,250
Real estate-construction [Member] | Grade:1. Cash secured/2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-construction [Member] | Grade:3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	6,241	3,907
Real estate-construction [Member] | Grade:4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	1,701	1,783
Real estate-construction [Member] | Grade:5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	31,900	26,331
Real estate-construction [Member] | Grade:6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	27,942	42,190
Real estate-construction [Member] | Grade:7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment		548
Real estate-construction [Member] | Grade:8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	16,243	16,491
Real estate-construction [Member] | Grade:9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-construction [Member] | Grade:10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-residential secured for business purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	32,329	35,179		32,097
Real estate-residential secured for business purpose [Member] | Grade:1. Cash secured/2. Fully secured [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-residential secured for business purpose [Member] | Grade:3. Strong [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-residential secured for business purpose [Member] | Grade:4. Satisfactory [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	113	335
Real estate-residential secured for business purpose [Member] | Grade:5. Acceptable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	23,593	22,764
Real estate-residential secured for business purpose [Member] | Grade:6. Pre-watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	4,412	8,458
Real estate-residential secured for business purpose [Member] | Grade:7. Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	1,902	288
Real estate-residential secured for business purpose [Member] | Grade:8. Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	2,309	3,334
Real estate-residential secured for business purpose [Member] | Grade:9. Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-residential secured for business purpose [Member] | Grade:10. Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment
Real estate-residential secured for personal purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	144,002	146,526
Real estate-residential secured for personal purpose [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	143,051	145,722
Real estate-residential secured for personal purpose [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	951	804
Real estate-home equity secured for personal purpose [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	84,109	82,727
Real estate-home equity secured for personal purpose [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	84,035	82,673
Real estate-home equity secured for personal purpose [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	74	54
Loans to individuals [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	43,598	43,780		44,037
Loans to individuals [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	43,370	43,395
Loans to individuals [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	228	385
Lease financings [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	91,621	83,857		75,255
Lease financings [Member] | Performing Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	91,236	83,412
Lease financings [Member] | Nonperforming Financing Receivable [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans and leases held for investment	$ 385	$ 445

[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.