Age Analysis of Past Due Loans (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	$ 26,306	$ 13,968
90 days or more past due	143,889	96,840
Total past due	170,195	110,808
Current	1,013,947	1,166,282
Ending balance	1,184,142	1,277,090	1,307,586
Loans 90 days or more past due and accruing	12	248
Commercial construction, land and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	228,220	250,859
Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	391,197	424,690
Residential Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	13,624	13,509
Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	228,588	245,180
Commercial, financial and agricultural
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	3,543	2,288
90 days or more past due	7,644	2,372
Total past due	11,187	4,660
Current	265,592	287,214
Ending balance	276,779	291,874	292,381
Loans 90 days or more past due and accruing	0	0
Commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	619,417	675,549	695,800
Commercial real estate | Commercial construction, land and land development
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	5,787	1,493
90 days or more past due	102,176	59,382
Total past due	107,963	60,875
Current	120,257	189,984
Ending balance	228,220	250,859
Loans 90 days or more past due and accruing	0	0
Commercial real estate | Other commercial real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	6,010	3,687
90 days or more past due	17,230	15,275
Total past due	23,240	18,962
Current	367,957	405,728
Ending balance	391,197	424,690
Loans 90 days or more past due and accruing	0	0
Consumer Portfolio Segment
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	618	546
90 days or more past due	659	651
Total past due	1,277	1,197
Current	44,457	49,781
Ending balance	45,734	50,978	53,600
Loans 90 days or more past due and accruing	0	0
Residential real estate
Financing Receivable, Recorded Investment, Past Due [Line Items]
Ending balance	242,212	258,689	265,805
Residential real estate | Residential Construction
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	337	0
90 days or more past due	484	497
Total past due	821	497
Current	12,803	13,012
Ending balance	13,624	13,509
Loans 90 days or more past due and accruing	0	0
Residential real estate | Residential Mortgage
Financing Receivable, Recorded Investment, Past Due [Line Items]
30-89 days past due	10,011	5,954
90 days or more past due	15,696	18,663
Total past due	25,707	24,617
Current	202,881	220,563
Ending balance	228,588	245,180
Loans 90 days or more past due and accruing	$ 12	$ 248