Loans - Summary of Impaired Financial Receivables (Analysis of Covered Impaired Loans) (Detail) (Covered Loans [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 296,665	$ 278,333	$ 335,784
Recorded Investment With No Allowance	120,107	188,441	134,906
Recorded Investment With Allowance
Total impaired loans	120,107	188,441	134,906
Related Allowance
Average Recorded Investment	127,507	184,162	163,825
Commercial, financial & agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	24,301	24,085	27,060
Recorded Investment With No Allowance	8,754	14,260	10,802
Recorded Investment With Allowance
Total impaired loans	8,754	14,260	10,802
Related Allowance
Average Recorded Investment	9,778	13,144	12,506
Real estate - construction & development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	78,421	59,102	85,279
Recorded Investment With No Allowance	23,978	37,831	23,236
Recorded Investment With Allowance
Total impaired loans	23,978	37,831	23,236
Related Allowance
Average Recorded Investment	23,607	36,097	29,970
Real estate - commercial & farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	139,197	128,389	159,493
Recorded Investment With No Allowance	55,822	90,847	64,231
Recorded Investment With Allowance
Total impaired loans	55,822	90,847	64,231
Related Allowance
Average Recorded Investment	60,026	87,793	78,790
Real estate - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	54,422	65,971	63,559
Recorded Investment With No Allowance	31,310	44,866	36,335
Recorded Investment With Allowance
Total impaired loans	31,310	44,866	36,335
Related Allowance
Average Recorded Investment	33,823	46,573	42,061
Consumer installment loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	324	786	393
Recorded Investment With No Allowance	243	637	302
Recorded Investment With Allowance
Total impaired loans	243	637	302
Related Allowance
Average Recorded Investment	$ 273	$ 555	$ 498