Loans - Analysis of Information Pertaining to Impaired Loans, Excluding Purchased Non-Covered and Covered 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, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 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	$ 2,006,916	$ 2,457,444
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	244,991	244,373
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	132,277	146,371
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	799,149	808,323
Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	436,515	366,882	355,920	436,515	355,920	366,882
Excluding Purchased Non-Covered and Covered Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	51,081	61,024	65,594	51,081	65,594	61,024
Recorded Investment With No Allowance	13,165	0	0	13,165	0	0
Recorded Investment With Allowance	26,906	46,417	48,744	26,906	48,744	46,417
Total impaired loans	40,071	46,417	48,744	40,071	48,744	46,417
Related Allowance	4,237	3,871	5,180	4,237	5,180	3,871
Average Recorded Investment	39,760	47,580	49,285	42,878	53,047	51,721
Excluding Purchased Non-Covered and Covered Loans [Member] | Commercial, Financial and Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	4,445	6,240	7,401	4,445	7,401	6,240
Recorded Investment With No Allowance	8	0	0	8	0	0
Recorded Investment With Allowance	2,943	4,618	4,719	2,943	4,719	4,618
Total impaired loans	2,951	4,618	4,719	2,951	4,719	4,618
Related Allowance	631	435	820	631	820	435
Average Recorded Investment	2,402	4,669	5,052	3,285	4,900	4,844
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Construction and Development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	8,824	11,363	14,299	8,824	14,299	11,363
Recorded Investment With No Allowance	211	0	0	211	0	0
Recorded Investment With Allowance	4,743	5,867	6,155	4,743	6,155	5,867
Total impaired loans	4,954	5,867	6,155	4,954	6,155	5,867
Related Allowance	612	512	821	612	821	512
Average Recorded Investment	5,243	6,011	6,775	5,596	8,960	8,341
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Commercial and Farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	18,955	18,456	18,628	18,955	18,628	18,456
Recorded Investment With No Allowance	7,311	0	0	7,311	0	0
Recorded Investment With Allowance	8,753	15,479	16,241	8,753	16,241	15,479
Total impaired loans	16,064	15,479	16,241	16,064	16,241	15,479
Related Allowance	1,698	1,443	1,999	1,698	1,999	1,443
Average Recorded Investment	16,242	15,860	16,366	16,312	18,079	17,559
Excluding Purchased Non-Covered and Covered Loans [Member] | Real Estate - Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	18,251	24,342	24,701	18,251	24,701	24,342
Recorded Investment With No Allowance	5,635	0	0	5,635	0	0
Recorded Investment With Allowance	9,946	19,970	21,174	9,946	21,174	19,970
Total impaired loans	15,581	19,970	21,174	15,581	21,174	19,970
Related Allowance	1,286	1,472	1,530	1,286	1,530	1,472
Average Recorded Investment	15,356	20,571	20,533	17,169	20,427	20,335
Excluding Purchased Non-Covered and Covered Loans [Member] | Consumer Installment Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid Contractual Principal Balance	606	623	565	606	565	623
Recorded Investment With No Allowance	0	0	0	0	0	0
Recorded Investment With Allowance	521	483	455	521	455	483
Total impaired loans	521	483	455	521	455	483
Related Allowance	10	9	10	10	10	9
Average Recorded Investment	$ 517	$ 469	$ 559	$ 516	$ 681	$ 642