Loans - Summary of Impaired Financial Receivables (Analysis of Non-Covered Impaired Loans) (Detail) (Non-Covered Loan [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	$ 77,144	$ 99,526	$ 78,758
Recorded Investment With No Allowance
Recorded Investment With Allowance	55,989	79,106	57,629
Total Recorded Investment	55,989	79,106	57,629
Related Allowance	4,839	9,500	5,115
Average Recorded Investment	56,808	83,940	70,209
Commercial, financial & agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	7,818	7,599	8,024
Recorded Investment With No Allowance
Recorded Investment With Allowance	4,555	4,732	4,940
Total Recorded Investment	4,555	4,732	4,940
Related Allowance	740	932	743
Average Recorded Investment	4,747	4,921	4,968
Real estate - construction & development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	20,633	20,593	20,316
Recorded Investment With No Allowance
Recorded Investment With Allowance	11,273	11,952	11,016
Total Recorded Investment	11,273	11,952	11,016
Related Allowance	922	1,993	910
Average Recorded Investment	11,144	13,812	11,706
Real estate - commercial & farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	22,996	45,098	25,076
Recorded Investment With No Allowance
Recorded Investment With Allowance	18,676	39,304	20,910
Total Recorded Investment	18,676	39,304	20,910
Related Allowance	1,816	3,615	2,191
Average Recorded Investment	19,793	42,155	30,638
Real estate - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	24,777	24,845	24,155
Recorded Investment With No Allowance
Recorded Investment With Allowance	20,792	21,843	19,848
Total Recorded Investment	20,792	21,843	19,848
Related Allowance	1,344	2,928	1,246
Average Recorded Investment	20,320	21,948	21,813
Consumer installment loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	920	1,391	1,187
Recorded Investment With No Allowance
Recorded Investment With Allowance	693	1,275	915
Total Recorded Investment	693	1,275	915
Related Allowance	17	32	25
Average Recorded Investment	$ 804	$ 1,104	$ 1,084