Allowance for Probable Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Loan portfolio by credit quality indicator
Portfolio, total	$ 5,660,578	$ 5,199,235
Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	5,372,266	4,942,387
Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	9,558	73,077
Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	33,010	35,619
Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	167,777	72,259
Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	77,967	75,893
Commercial Loan [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,259,383	1,042,642
Commercial Loan [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,165,427	955,522
Commercial Loan [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	992	2,270
Commercial Loan [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,759	4,389
Commercial Loan [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	51,010	46,278
Commercial Loan [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	40,195	34,183
Commercial Real Estate Other Construction and Land Development Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,413,912	1,208,508
Commercial Real Estate Other Construction and Land Development Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,347,079	1,167,295
Commercial Real Estate Other Construction and Land Development Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	340	14,247
Commercial Real Estate Other Construction and Land Development Receivable [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	10,561	9,318
Commercial Real Estate Other Construction and Land Development Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	44,397	3,672
Commercial Real Estate Other Construction and Land Development Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	11,535	13,976
Commercial Real Estate Farmland and Commercial Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,745,580	1,750,039
Commercial Real Estate Farmland and Commercial Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,630,133	1,635,179
Commercial Real Estate Farmland and Commercial Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	8,114	56,438
Commercial Real Estate Farmland and Commercial Receivable [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	20,690	21,912
Commercial Real Estate Farmland and Commercial Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	70,872	20,472
Commercial Real Estate Farmland and Commercial Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	15,771	16,038
Commercial Real Estate Multifamily Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	100,719	102,098
Commercial Real Estate Multifamily Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	99,649	100,948
Commercial Real Estate Multifamily Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	819	855
Commercial Real Estate Multifamily Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	251	295
Residential First Mortgage Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	417,558	438,462
Residential First Mortgage Financing Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	411,888	432,067
Residential First Mortgage Financing Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	112	122
Residential First Mortgage Financing Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	101	120
Residential First Mortgage Financing Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	5,457	6,153
Residential Second Mortgage Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	470,176	409,230
Residential Second Mortgage Financing Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	466,798	405,731
Residential Second Mortgage Financing Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	445	293
Residential Second Mortgage Financing Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	2,933	3,206
Consumer Loan [Member]
Loan portfolio by credit quality indicator
Portfolio, total	61,993	66,414
Consumer Loan [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	60,452	64,808
Consumer Loan [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	133
Consumer Loan [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,408	1,606
Foreign Receivables [Member]
Loan portfolio by credit quality indicator
Portfolio, total	191,257	181,842
Foreign Receivables [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	190,840	180,837
Foreign Receivables [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total		569
Foreign Receivables [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	$ 417	$ 436