Loans and Leases - Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	$ 51,846	$ 52,598
Impaired loans with an allowance recorded, Recorded Investment	7,233	5,735
Impaired loans with no related allowance, Unpaid Principal Balance	54,684	62,486
Impaired loans with an allowance recorded, Unpaid Principal Balance	7,233	5,798
Total impaired loans, Recorded Investment	59,079	58,333
Total impaired loans, Unpaid Principal Balance	61,917	68,284
Total impaired loans, Related Allowance	1,142	2,963
Commercial, Financial and Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	14,777	10,890
Impaired loans with an allowance recorded, Recorded Investment	3,437	3,215
Impaired loans with no related allowance, Unpaid Principal Balance	15,213	11,749
Impaired loans with an allowance recorded, Unpaid Principal Balance	3,437	3,272
Total impaired loans, Recorded Investment	18,214	14,105
Total impaired loans, Unpaid Principal Balance	18,650	15,021
Total impaired loans, Related Allowance	685	2,398
Real Estate-Commercial [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	27,430	28,883
Impaired loans with an allowance recorded, Recorded Investment	2,246	0
Impaired loans with no related allowance, Unpaid Principal Balance	28,545	35,700
Impaired loans with an allowance recorded, Unpaid Principal Balance	2,246	0
Total impaired loans, Recorded Investment	29,676	28,883
Total impaired loans, Unpaid Principal Balance	30,791	35,700
Total impaired loans, Related Allowance	27	0
Real Estate-Construction [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	7,665	12,357
Impaired loans with no related allowance, Unpaid Principal Balance	8,902	14,540
Total impaired loans, Recorded Investment	7,665	12,357
Total impaired loans, Unpaid Principal Balance	8,902	14,540
Total impaired loans, Related Allowance	0	0
Real Estate-Residential Secured for Business Purpose [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	1,371	224
Impaired loans with an allowance recorded, Recorded Investment	1,550	1,550
Impaired loans with no related allowance, Unpaid Principal Balance	1,400	235
Impaired loans with an allowance recorded, Unpaid Principal Balance	1,550	1,550
Total impaired loans, Recorded Investment	2,921	1,774
Total impaired loans, Unpaid Principal Balance	2,950	1,785
Total impaired loans, Related Allowance	430	501
Real Estate-Residential Secured for Personal Purpose [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	526	131
Impaired loans with an allowance recorded, Recorded Investment	0	970
Impaired loans with no related allowance, Unpaid Principal Balance	547	131
Impaired loans with an allowance recorded, Unpaid Principal Balance	0	976
Total impaired loans, Recorded Investment	526	1,101
Total impaired loans, Unpaid Principal Balance	547	1,107
Total impaired loans, Related Allowance	0	64
Real Estate-Home Equity Secured for Personal Purpose [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	77	77
Impaired loans with no related allowance, Unpaid Principal Balance	77	77
Total impaired loans, Recorded Investment	77	77
Total impaired loans, Unpaid Principal Balance	77	77
Total impaired loans, Related Allowance	0	0
Loans to Individuals [Member]
Financing Receivable, Impaired [Line Items]
Impaired loans with no related allowance, Recorded Investment	0	36
Impaired loans with no related allowance, Unpaid Principal Balance	0	54
Total impaired loans, Recorded Investment	0	36
Total impaired loans, Unpaid Principal Balance	0	54
Total impaired loans, Related Allowance	$ 0	$ 0