Loans - Schedule of Allowances for Loan Losses By Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 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	2,603	12,600	28,451
Loans charged off	(3,036)	(19,337)	(41,163)
Recoveries of loans previously charged off	222	270	1,149
Ending balance	23,382	28,689	23,593
Period-end amount allocated to: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	4,409	8,360	4,554
Loans collectively evaluated for impairment	18,973	20,329	19,039
Ending balance	23,382	28,689	23,593
Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	45,229	65,286	45,320
Collectively evaluated for impairment	1,447,524	1,258,558	1,405,315
Ending balance	1,492,753	1,323,844	1,450,635
Commercial, financial & 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	254	(693)	815
Loans charged off	(410)	(155)	(1,451)
Recoveries of loans previously charged off	84	48	157
Ending balance	2,367	2,118	2,439
Commercial, financial & agricultural [Member] | Period-end amount allocated to: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	675	827	659
Loans collectively evaluated for impairment	1,692	1,291	1,780
Ending balance	2,367	2,118	2,439
Commercial, financial & agricultural [Member] | Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,334	3,220	3,351
Collectively evaluated for impairment	177,554	146,100	170,866
Ending balance	180,888	149,320	174,217
Real estate - construction & 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	1,467	1,967	5,245
Loans charged off	(655)	(3,930)	(9,380)
Recoveries of loans previously charged off	2	17	40
Ending balance	6,157	7,492	5,343
Real estate - construction & development [Member] | Period-end amount allocated to: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	641	1,450	611
Loans collectively evaluated for impairment	5,516	6,042	4,732
Ending balance	6,157	7,492	5,343
Real estate - construction & development [Member] | Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	8,281	8,980	7,617
Collectively evaluated for impairment	121,880	113,351	106,582
Ending balance	130,161	122,331	114,199
Real estate - commercial & 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	696	8,585	15,000
Loans charged off	(1,025)	(12,964)	(20,551)
Recoveries of loans previously charged off	3	16	482
Ending balance	8,831	9,863	9,157
Real estate - commercial & farmland [Member] | Period-end amount allocated to: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans individually evaluated for impairment	1,890	3,421	2,228
Loans collectively evaluated for impairment	6,941	6,442	6,929
Ending balance	8,831	9,863	9,157
Real estate - commercial & farmland [Member] | Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	19,545	35,971	21,332
Collectively evaluated for impairment	746,682	622,083	710,990
Ending balance	766,227	658,054	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	339	2,002	6,267
Loans charged off	(779)	(2,123)	(8,722)
Recoveries of loans previously charged off	85	141	225
Ending balance	5,543	8,148	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	1,203	2,659	1,056
Loans collectively evaluated for impairment	4,340	5,489	4,842
Ending balance	5,543	8,148	5,898
Real estate - residential [Member] | Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	14,069	17,098	13,020
Collectively evaluated for impairment	341,647	310,955	333,460
Ending balance	355,716	328,053	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	(153)	739	1,124
Loans charged off	(167)	(165)	(1,059)
Recoveries of loans previously charged off	48	48	245
Ending balance	484	1,068	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	484	1,065	756
Ending balance	484	1,068	756
Consumer Installment and Other [Member] | Loans: [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment		17
Collectively evaluated for impairment	59,761	66,069	83,417
Ending balance	$ 59,761	$ 66,086	$ 83,417