Loans - Schedule of Allowances for Loan Losses By Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 23,593	$ 35,156	$ 35,156
Provision for loan losses	8,747	24,360	28,451
Loans charged off	(9,693)	(34,167)	(41,163)
Recoveries of loans previously charged off	1,207	552	1,149
Ending balance	23,854	25,901	23,593
Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	4,849	5,556	4,554
Loans collectively evaluated for impairment	19,005	20,345	19,039
Ending balance	23,854	25,901	23,593
Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	38,705	44,988	45,320
Collectively evaluated for impairment	1,550,562	1,394,874	1,405,315
Ending balance	1,589,267	1,439,862	1,450,635
Commercial, Financial and Agricultural [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	2,439	2,918	2,918
Provision for loan losses	1,011	677	815
Loans charged off	(1,216)	(889)	(1,451)
Recoveries of loans previously charged off	340	101	157
Ending balance	2,574	2,807	2,439
Commercial, Financial and Agricultural [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	741	610	659
Loans collectively evaluated for impairment	1,833	2,197	1,780
Ending balance	2,574	2,807	2,439
Commercial, Financial and Agricultural [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,657	2,748	3,351
Collectively evaluated for impairment	241,334	186,626	170,866
Ending balance	244,991	189,374	174,217
Real Estate - Construction and Development [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,343	9,438	9,438
Provision for loan losses	2,127	4,954	5,245
Loans charged off	(1,598)	(7,819)	(9,380)
Recoveries of loans previously charged off	88	23	40
Ending balance	5,960	6,596	5,343
Real Estate - Construction and Development [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	682	526	611
Loans collectively evaluated for impairment	5,278	6,070	4,732
Ending balance	5,960	6,596	5,343
Real Estate - Construction and Development [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,524	5,510	7,617
Collectively evaluated for impairment	128,753	119,805	106,582
Ending balance	132,277	125,315	114,199
Real Estate - Commercial and Farmland [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	9,157	14,226	14,226
Provision for loan losses	2,632	13,087	15,000
Loans charged off	(2,873)	(18,199)	(20,551)
Recoveries of loans previously charged off	18	32	482
Ending balance	8,934	9,146	9,157
Real Estate - Commercial and Farmland [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,997	2,315	2,228
Loans collectively evaluated for impairment	6,937	6,831	6,929
Ending balance	8,934	9,146	9,157
Real Estate - Commercial and Farmland [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	14,605	21,552	21,332
Collectively evaluated for impairment	784,544	691,688	710,990
Ending balance	799,149	713,240	732,322
Real Estate - Residential [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	5,898	8,128	8,128
Provision for loan losses	2,966	4,936	6,267
Loans charged off	(3,430)	(6,642)	(8,722)
Recoveries of loans previously charged off	520	199	225
Ending balance	5,954	6,621	5,898
Real Estate - Residential [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,429	2,105	1,056
Loans collectively evaluated for impairment	4,525	4,516	4,842
Ending balance	5,954	6,621	5,898
Real Estate - Residential [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	16,919	15,178	13,020
Collectively evaluated for impairment	339,001	328,154	333,460
Ending balance	355,920	343,332	346,480
Consumer Installment Loans and Other [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	756	446	446
Provision for loan losses	11	706	1,124
Loans charged off	(576)	(618)	(1,059)
Recoveries of loans previously charged off	241	197	245
Ending balance	432	731	756
Consumer Installment Loans and Other [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans collectively evaluated for impairment	432	731	756
Ending balance	432	731	756
Consumer Installment Loans and Other [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Collectively evaluated for impairment	56,930	68,601	83,417
Ending balance	$ 56,930	$ 68,601	$ 83,417