Allowance for Probable Loan Losses (Details 6) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Loan portfolio by credit quality indicator
Portfolio, total	$ 4,775,004	$ 5,053,475
Pass
Loan portfolio by credit quality indicator
Portfolio, total	4,369,031	4,496,404
Special Review
Loan portfolio by credit quality indicator
Portfolio, total	169,097	165,714
Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	65,855	59,349
Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	88,016	195,703
Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	83,005	136,305
Commercial
Loan portfolio by credit quality indicator
Portfolio, total	769,110	773,816
Commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	675,263	655,154
Commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	4,278	5,279
Commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	16,535	6,361
Commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	40,266	79,419
Commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	32,768	27,603
Commercial real estate: other construction and land development
Loan portfolio by credit quality indicator
Portfolio, total	1,147,669	1,273,389
Commercial real estate: other construction and land development \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,038,749	1,058,843
Commercial real estate: other construction and land development \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	55,079	76,722
Commercial real estate: other construction and land development \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	2,614	11,083
Commercial real estate: other construction and land development \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	22,567	66,313
Commercial real estate: other construction and land development \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	28,660	60,428
Commercial real estate: farmland and commercial
Loan portfolio by credit quality indicator
Portfolio, total	1,673,322	1,664,687
Commercial real estate: farmland and commercial \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	1,486,572	1,449,822
Commercial real estate: farmland and commercial \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	109,144	83,581
Commercial real estate: farmland and commercial \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	46,316	40,510
Commercial real estate: farmland and commercial \| Watch List - Substandard
Loan portfolio by credit quality indicator
Portfolio, total	17,345	48,543
Commercial real estate: farmland and commercial \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	13,945	42,231
Commercial real estate: multifamily
Loan portfolio by credit quality indicator
Portfolio, total	82,948	121,599
Commercial real estate: multifamily \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	82,542	121,188
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	353	411
Residential: first lien
Loan portfolio by credit quality indicator
Portfolio, total	456,731	495,722
Residential: first lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	446,218	490,924
Residential: first lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	519	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	6,338	1,402
Residential: first lien \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	3,656	2,290
Residential: junior lien
Loan portfolio by credit quality indicator
Portfolio, total	381,736	400,148
Residential: junior lien \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	378,000	397,861
Residential: junior lien \| Special Review
Loan portfolio by credit quality indicator
Portfolio, total	77
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	1,850	1,962
Consumer
Loan portfolio by credit quality indicator
Portfolio, total	74,514	94,109
Consumer \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	73,188	92,714
Consumer \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total		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	1,326	1,334
Foreign
Loan portfolio by credit quality indicator
Portfolio, total	188,974	230,005
Foreign \| Pass
Loan portfolio by credit quality indicator
Portfolio, total	188,499	229,898
Foreign \| Watch List - Pass
Loan portfolio by credit quality indicator
Portfolio, total	28	61
Foreign \| Watch List - Impaired
Loan portfolio by credit quality indicator
Portfolio, total	$ 447	$ 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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