Allowance for Probable Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Loan portfolio by credit quality indicator
Portfolio, total	$ 5,437,515	$ 5,199,235
Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	5,148,115	4,942,387
Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	10,739	73,077
Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	33,751	35,619
Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	170,002	72,259
Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	74,908	75,893
Commercial Loan [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,152,130	1,042,642
Commercial Loan [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,058,402	955,522
Commercial Loan [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,017	2,270
Commercial Loan [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	2,270	4,389
Commercial Loan [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	52,369	46,278
Commercial Loan [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	38,072	34,183
Commercial Real Estate Other Construction And Land Development Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,324,207	1,208,508
Commercial Real Estate Other Construction And Land Development Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,257,444	1,167,295
Commercial Real Estate Other Construction And Land Development Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	344	14,247
Commercial Real Estate Other Construction And Land Development Receivable [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	10,835	9,318
Commercial Real Estate Other Construction And Land Development Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	44,064	3,672
Commercial Real Estate Other Construction And Land Development Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	11,520	13,976
Commercial Real Estate Farmland And Commercial Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,744,316	1,750,039
Commercial Real Estate Farmland And Commercial Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,627,979	1,635,179
Commercial Real Estate Farmland And Commercial Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	9,264	56,438
Commercial Real Estate Farmland And Commercial Receivable [Member] \| Special Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	20,646	21,912
Commercial Real Estate Farmland And Commercial Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	71,963	20,472
Commercial Real Estate Farmland And Commercial Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	14,464	16,038
Commercial Real Estate Multifamily Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	103,981	102,098
Commercial Real Estate Multifamily Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	102,887	100,948
Commercial Real Estate Multifamily Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	828	855
Commercial Real Estate Multifamily Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	266	295
Residential First Mortgage Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	413,604	438,462
Residential First Mortgage Financing Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	407,780	432,067
Residential First Mortgage Financing Receivable [Member] \| Special Mention [Member]
Loan portfolio by credit quality indicator
Portfolio, total	114	122
Residential First Mortgage Financing Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	21	120
Residential First Mortgage Financing Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	5,689	6,153
Residential Second Mortgage Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	447,263	409,230
Residential Second Mortgage Financing Receivable [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	443,702	405,731
Residential Second Mortgage Financing Receivable [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	451	293
Residential Second Mortgage Financing Receivable [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	3,110	3,206
Consumer Loan [Member]
Loan portfolio by credit quality indicator
Portfolio, total	62,885	66,414
Consumer Loan [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	61,522	64,808
Consumer Loan [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	1,363	1,606
Foreign Receivables [Member]
Loan portfolio by credit quality indicator
Portfolio, total	189,129	181,842
Foreign Receivables [Member] \| Pass [Member]
Loan portfolio by credit quality indicator
Portfolio, total	188,399	180,837
Foreign Receivables [Member] \| Substandard [Member]
Loan portfolio by credit quality indicator
Portfolio, total	306	569
Foreign Receivables [Member] \| Nonperforming Financing Receivable [Member]
Loan portfolio by credit quality indicator
Portfolio, total	$ 424	$ 436