Allowance for Probable Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Loan portfolio by credit quality indicator
Portfolio, total	$ 4,883,028	$ 5,053,475
Pass
Loan portfolio by credit quality indicator
Portfolio, total	4,502,971	4,496,404
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	107,814	165,714
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	53,984	59,349
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	132,835	195,703
Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	85,424	136,305
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	816,716	773,816
Commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	698,626	655,154
Commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	5,154	5,279
Commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	4,956	6,361
Commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	84,464	79,419
Commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	23,516	27,603
Commercial real estate: other construction and land development
Loan portfolio by credit quality indicator
Portfolio, total	1,192,273	1,273,389
Commercial real estate: other construction and land development \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,116,692	1,058,843
Commercial real estate: other construction and land development \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	14,810	76,722
Commercial real estate: other construction and land development \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	6,711	11,083
Commercial real estate: other construction and land development \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	20,111	66,313
Commercial real estate: other construction and land development \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	33,949	60,428
Commercial real estate: farmland and commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,670,931	1,664,687
Commercial real estate: farmland and commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,500,498	1,449,822
Commercial real estate: farmland and commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	87,246	83,581
Commercial real estate: farmland and commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	41,935	40,510
Commercial real estate: farmland and commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	20,370	48,543
Commercial real estate: farmland and commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	20,882	42,231
Commercial real estate: multifamily
Loan portfolio by credit quality indicator
Portfolio, total	97,533	121,599
Commercial real estate: multifamily \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	97,111	121,188
Commercial real estate: multifamily \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	54
Commercial real estate: multifamily \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	368	411
Residential: first lien
Loan portfolio by credit quality indicator
Portfolio, total	451,308	495,722
Residential: first lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	440,959	490,924
Residential: first lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	526	132
Residential: first lien \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		974
Residential: first lien \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	6,336	1,402
Residential: first lien \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	3,487	2,290
Residential: junior lien
Loan portfolio by credit quality indicator
Portfolio, total	381,831	400,148
Residential: junior lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	378,087	397,861
Residential: junior lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	78
Residential: junior lien \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	309	319
Residential: junior lien \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	1,500	6
Residential: junior lien \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,857	1,962
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	79,454	94,109
Consumer \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	78,146	92,714
Consumer \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	35	41
Consumer \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total		20
Consumer \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	1,273	1,334
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	192,982	230,005
Foreign \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	192,852	229,898
Foreign \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	38	61
Foreign \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 92	$ 46

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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