Loans - Analysis of Information Pertaining to Purchased Non-Covered Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 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	$ 2,836,072	$ 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	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	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	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	436,515	366,882	355,920
Purchased Non-Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	26,380	10,996	26,380	10,996
Recorded Investment With No Allowance	17,590	6,659	17,590	6,659
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	17,590	6,659	17,590	6,659
Related Allowance	0	0	0	0
Average Recorded Investment	16,680	507	13,834	128
Purchased Non-Covered Loans [Member] | Commercial, Financial and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	438	19	438	19
Recorded Investment With No Allowance	54	11	54	11
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	54	11	54	11
Related Allowance	0	0	0	0
Average Recorded Investment	98	1	81	0
Purchased Non-Covered Loans [Member] | Real Estate - Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	3,794	542	3,794	542
Recorded Investment With No Allowance	2,274	325	2,274	325
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	2,274	325	2,274	325
Related Allowance	0	0	0	0
Average Recorded Investment	2,273	25	1,501	6
Purchased Non-Covered Loans [Member] | Real Estate - Commercial and Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	12,354	2,673	12,354	2,673
Recorded Investment With No Allowance	8,776	1,653	8,776	1,653
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	8,776	1,653	8,776	1,653
Related Allowance	0	0	0	0
Average Recorded Investment	7,712	126	5,976	32
Purchased Non-Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	9,610	7,712	9,610	7,712
Recorded Investment With No Allowance	6,407	4,658	6,407	4,658
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	6,407	4,658	6,407	4,658
Related Allowance	0	0	0	0
Average Recorded Investment	6,533	354	6,233	90
Purchased Non-Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	184	20	184	20
Recorded Investment With No Allowance	79	12	79	12
Recorded Investment With Allowance	0	0	0	0
Total Recorded Investment	79	12	79	12
Related Allowance	0	0	0	0
Average Recorded Investment	$ 64	$ 1	$ 43