Loans - Summary of Impaired Financial Receivables (Analysis of Covered Impaired Loans) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	$ 2,836,072	$ 2,457,444	$ 2,006,916	$ 2,836,072	$ 2,457,444	$ 2,006,916
Commercial, Financial and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	334,783	244,373	244,991	334,783	244,373	244,991
Real Estate - Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	154,315	146,371	132,277	154,315	146,371	132,277
Real Estate - Commercial and Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	882,160	808,323	799,149	882,160	808,323	799,149
Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	436,515	366,882	355,920	436,515	366,882	355,920
Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	71,713	106,690	115,633	71,713	106,690	115,633
Recorded Investment With No Allowance	62,040	91,395	96,095	62,040	91,395	96,095
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	62,040	91,395	96,095	62,040	91,395	96,095
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	64,641	93,745	103,872	75,808	110,830	115,689
Covered Loans [Member] | Commercial, Financial and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	11,356	9,680	10,645	11,356	9,680	10,645
Recorded Investment With No Allowance	8,467	7,270	7,884	8,467	7,270	7,884
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	8,467	7,270	7,884	8,467	7,270	7,884
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	10,367	7,577	8,327	9,511	8,696	9,052
Covered Loans [Member] | Real Estate - Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	13,268	20,915	25,401	13,268	20,915	25,401
Recorded Investment With No Allowance	11,920	18,037	20,890	11,920	18,037	20,890
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	11,920	18,037	20,890	11,920	18,037	20,890
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	11,484	19,464	21,860	14,760	21,794	22,734
Covered Loans [Member] | Real Estate - Commercial and Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	26,624	46,612	51,105	26,624	46,612	51,105
Recorded Investment With No Allowance	23,118	40,749	43,279	23,118	40,749	43,279
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	23,118	40,749	43,279	23,118	40,749	43,279
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	23,562	42,014	48,558	29,904	51,584	54,292
Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	20,331	29,089	28,078	20,331	29,089	28,078
Recorded Investment With No Allowance	18,430	24,998	23,692	18,430	24,998	23,692
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	18,430	24,998	23,692	18,430	24,998	23,692
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	19,112	24,345	24,810	21,456	28,452	29,316
Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	134	394	404	134	394	404
Recorded Investment With No Allowance	105	341	350	105	341	350
Recorded Investment With Allowance	0	0	0	0	0	0
Total Recorded Investment	105	341	350	105	341	350
Related Allowance	0	0	0	0	0	0
Average Recorded Investment	$ 116	$ 346	$ 318	$ 177	$ 304	$ 295