Loans - Schedule of Allowances for Loan Losses By Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 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	6,298	18,670	28,451
Loans charged off	(6,236)	(28,075)	(41,163)
Recoveries of loans previously charged off	562	447	1,149
Ending balance	24,217	26,198	23,593
Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	4,545	6,632	4,554
Loans collectively evaluated for impairment	19,672	19,566	19,039
Ending balance	24,217	26,198	23,593
Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	38,811	53,891	45,320
Collectively evaluated for impairment	1,517,016	1,311,598	1,405,315
Ending balance	1,555,827	1,365,489	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	1,118	425	815
Loans charged off	(734)	(654)	(1,451)
Recoveries of loans previously charged off	128	78	157
Ending balance	2,951	2,767	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	876	623	659
Loans collectively evaluated for impairment	2,075	2,144	1,780
Ending balance	2,951	2,767	2,439
Commercial, Financial and Agricultural [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,705	2,776	3,351
Collectively evaluated for impairment	204,719	172,127	170,866
Ending balance	208,424	174,903	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	1,526	1,795	5,245
Loans charged off	(1,231)	(5,211)	(9,380)
Recoveries of loans previously charged off	4	19	40
Ending balance	5,642	6,041	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	467	898	611
Loans collectively evaluated for impairment	5,175	5,143	4,732
Ending balance	5,642	6,041	5,343
Real Estate - Construction and Development [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,935	7,173	7,617
Collectively evaluated for impairment	130,672	117,383	106,582
Ending balance	134,607	124,556	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	1,420	11,153	15,000
Loans charged off	(1,793)	(17,484)	(20,551)
Recoveries of loans previously charged off	13	24	482
Ending balance	8,797	7,919	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	1,629	1,999	2,228
Loans collectively evaluated for impairment	7,168	5,920	6,929
Ending balance	8,797	7,919	9,157
Real Estate - Commercial and Farmland [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	15,842	24,838	21,332
Collectively evaluated for impairment	772,812	650,566	710,990
Ending balance	788,654	675,404	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	2,340	3,751	6,267
Loans charged off	(2,107)	(4,374)	(8,722)
Recoveries of loans previously charged off	229	162	225
Ending balance	6,360	7,667	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	1,573	3,109	1,056
Loans collectively evaluated for impairment	4,787	4,558	4,842
Ending balance	6,360	7,667	5,898
Real Estate - Residential [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	15,329	19,088	13,020
Collectively evaluated for impairment	342,356	313,036	333,460
Ending balance	357,685	332,124	346,480
Consumer Installment and Other [Member] | Loans Receivable [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	756	446	446
Provision for loan losses	(106)	1,546	1,124
Loans charged off	(371)	(352)	(1,059)
Recoveries of loans previously charged off	188	164	245
Ending balance	467	1,804	756
Consumer Installment and Other [Member] | Period-End Amount Allocated to [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment		3
Loans collectively evaluated for impairment	467	1,801	756
Ending balance	467	1,804	756
Consumer Installment and Other [Member] | Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment		16
Collectively evaluated for impairment	66,457	58,486	83,417
Ending balance	$ 66,457	$ 58,502	$ 83,417