Allowance for Probable Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Loan portfolio by credit quality indicator
Portfolio, total	$ 4,911,949	$ 4,775,004
Pass
Loan portfolio by credit quality indicator
Portfolio, total	4,530,216	4,369,031
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	155,200	169,097
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	38,133	65,855
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	102,102	88,016
Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	86,298	83,005
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	876,998	769,110
Commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	777,045	675,263
Commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	4,317	4,278
Commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	16,048	16,535
Commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	44,468	40,266
Commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	35,120	32,768
Commercial real estate: other construction and land development
Loan portfolio by credit quality indicator
Portfolio, total	1,142,868	1,147,669
Commercial real estate: other construction and land development \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,052,052	1,038,749
Commercial real estate: other construction and land development \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	37,332	55,079
Commercial real estate: other construction and land development \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,920	2,614
Commercial real estate: other construction and land development \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	25,074	22,567
Commercial real estate: other construction and land development \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	26,490	28,660
Commercial real estate: farmland and commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,730,060	1,673,322
Commercial real estate: farmland and commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,557,457	1,486,572
Commercial real estate: farmland and commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	110,783	109,144
Commercial real estate: farmland and commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	20,165	46,316
Commercial real estate: farmland and commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	25,057	17,345
Commercial real estate: farmland and commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	16,598	13,945
Commercial real estate: multifamily
Loan portfolio by credit quality indicator
Portfolio, total	81,937	82,948
Commercial real estate: multifamily \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	81,613	82,542
Commercial real estate: multifamily \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		53
Commercial real estate: multifamily \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	324	353
Residential: first lien
Loan portfolio by credit quality indicator
Portfolio, total	445,848	456,731
Residential: first lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	435,272	446,218
Residential: first lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	509	519
Residential: first lien \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	5,700	6,338
Residential: first lien \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	4,367	3,656
Residential: junior lien
Loan portfolio by credit quality indicator
Portfolio, total	381,665	381,736
Residential: junior lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	378,075	378,000
Residential: junior lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	76	77
Residential: junior lien \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		309
Residential: junior lien \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	1,803	1,500
Residential: junior lien \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,711	1,850
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	68,077	74,514
Consumer \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	66,838	73,188
Consumer \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,239	1,326
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	184,496	188,974
Foreign \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	181,864	188,499
Foreign \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	2,183
Foreign \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		28
Foreign \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 449	$ 447

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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