Loans and Allowance for Credit Losses - Allowance for Credit Losses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	$ 67,187	$ 61,234	$ 71,229
Charge-offs	(35,178)	(16,969)	(68,293)
Recoveries	2,989	2,378	2,482
Provision for credit losses	19,227	20,544	55,816
Ending Balance	54,225	67,187	61,234
Ending balance: individually evaluated for impaired	8,824	17,778	13,236
Ending balance: collectively evaluated for impaired	45,401	49,409	47,998
Ending balance	4,283,833	4,204,704	4,043,643
Ending balance: individually evaluated for impaired	52,595	100,187	94,744
Ending balance: collectively evaluated for impaired	4,231,238	4,104,517	3,948,899
Commercial, financial, agricultural and other [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	19,852	18,200	21,700
Charge-offs	(18,399)	(5,207)	(7,114)
Recoveries	455	443	473
Provision for credit losses	20,755	6,416	3,141
Ending Balance	22,663	19,852	18,200
Ending balance: individually evaluated for impaired	7,364	10,331	9,069
Ending balance: collectively evaluated for impaired	15,299	9,521	9,131
Ending balance	1,021,056	1,019,822	996,739
Ending balance: individually evaluated for impaired	27,251	33,443	37,639
Ending balance: collectively evaluated for impaired	993,805	986,379	959,100
Real estate construction [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	8,928	6,756	18,002
Charge-offs	(773)	(3,601)	(28,886)
Recoveries	501	582	955
Provision for credit losses	(2,056)	5,191	16,685
Ending Balance	6,600	8,928	6,756
Ending balance: individually evaluated for impaired	94	300	2,960
Ending balance: collectively evaluated for impaired	6,506	8,628	3,796
Ending balance	93,289	87,438	76,564
Ending balance: individually evaluated for impaired	3,844	11,177	14,667
Ending balance: collectively evaluated for impaired	89,445	76,261	61,897
Residential real estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	5,908	8,237	5,454
Charge-offs	(1,814)	(3,828)	(4,107)
Recoveries	1,264	422	132
Provision for credit losses	2,369	1,077	6,758
Ending Balance	7,727	5,908	8,237
Ending balance: individually evaluated for impaired	1,282	780	93
Ending balance: collectively evaluated for impaired	6,445	5,128	8,144
Ending balance	1,262,718	1,241,565	1,137,059
Ending balance: individually evaluated for impaired	9,349	6,444	2,606
Ending balance: collectively evaluated for impaired	1,253,369	1,235,121	1,134,453
Commercial real estate [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	22,441	18,961	16,913
Charge-offs	(10,513)	(851)	(24,861)
Recoveries	136	410	349
Provision for credit losses	(286)	3,921	26,560
Ending Balance	11,778	22,441	18,961
Ending balance: individually evaluated for impaired	84	6,367	1,114
Ending balance: collectively evaluated for impaired	11,694	16,074	17,847
Ending balance	1,296,472	1,273,661	1,267,432
Ending balance: individually evaluated for impaired	12,151	49,123	39,832
Ending balance: collectively evaluated for impaired	1,284,321	1,224,538	1,227,600
Loans to individuals [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	4,132	4,244	4,215
Charge-offs	(3,679)	(3,482)	(3,325)
Recoveries	633	521	573
Provision for credit losses	4,371	2,849	2,781
Ending Balance	5,457	4,132	4,244
Ending balance: individually evaluated for impaired	0	0	0
Ending balance: collectively evaluated for impaired	5,457	4,132	4,244
Ending balance	610,298	582,218	565,849
Ending balance: individually evaluated for impaired	0	0	0
Ending balance: collectively evaluated for impaired	610,298	582,218	565,849
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Beginning Balance	5,926	4,836	4,945
Charge-offs	0	0	0
Recoveries	0	0	0
Provision for credit losses	(5,926)	1,090	(109)
Ending Balance	0	5,926	4,836
Ending balance: individually evaluated for impaired	0	0	0
Ending balance: collectively evaluated for impaired	$ 0	$ 5,926	$ 4,836