Allowance for Probable Loan Losses (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Financing receivable recorded investment
Past due 30-59 days	$ 27,332	$ 48,472
Past due 60-89 days	34,935	19,594
Past due 90 days or greater	91,243	71,614
Past due 90 days or greater and still accruing	15,781	14,288
Past due, total	153,510	139,680
Loans, current	4,781,972	4,913,795
Portfolio, total	4,935,482	5,053,475
Commercial
Financing receivable recorded investment
Past due 30-59 days	4,715	5,180
Past due 60-89 days	2,737	1,369
Past due 90 days or greater	1,478	1,842
Past due 90 days or greater and still accruing	1,383	1,490
Past due, total	8,930	8,391
Loans, current	790,705	765,425
Portfolio, total	799,635	773,816
Commercial real estate: other construction and land development
Financing receivable recorded investment
Past due 30-59 days	4,215	23,426
Past due 60-89 days	19,397	4,360
Past due 90 days or greater	62,279	49,887
Past due 90 days or greater and still accruing	391	979
Past due, total	85,891	77,673
Loans, current	1,183,255	1,195,716
Portfolio, total	1,269,146	1,273,389
Commercial real estate: farmland and commercial
Financing receivable recorded investment
Past due 30-59 days	8,613	9,467
Past due 60-89 days	8,416	10,269
Past due 90 days or greater	15,537	7,879
Past due 90 days or greater and still accruing	3,698	1,231
Past due, total	32,566	27,615
Loans, current	1,563,155	1,637,072
Portfolio, total	1,595,721	1,664,687
Commercial real estate: multifamily
Financing receivable recorded investment
Past due 30-59 days	370	450
Past due 90 days or greater	397	411
Past due, total	767	861
Loans, current	100,478	120,738
Portfolio, total	101,245	121,599
Residential: first lien
Financing receivable recorded investment
Past due 30-59 days	5,319	6,207
Past due 60-89 days	3,662	2,757
Past due 90 days or greater	10,367	10,295
Past due 90 days or greater and still accruing	9,256	9,382
Past due, total	19,348	19,259
Loans, current	457,351	476,463
Portfolio, total	476,699	495,722
Residential: junior lien
Financing receivable recorded investment
Past due 30-59 days	865	1,433
Past due 60-89 days	104	378
Past due 90 days or greater	421	368
Past due 90 days or greater and still accruing	332	320
Past due, total	1,390	2,179
Loans, current	386,098	397,969
Portfolio, total	387,488	400,148
Consumer
Financing receivable recorded investment
Past due 30-59 days	1,339	1,643
Past due 60-89 days	526	408
Past due 90 days or greater	762	912
Past due 90 days or greater and still accruing	719	866
Past due, total	2,627	2,963
Loans, current	85,033	91,146
Portfolio, total	87,660	94,109
Foreign
Financing receivable recorded investment
Past due 30-59 days	1,896	666
Past due 60-89 days	93	53
Past due 90 days or greater	2	20
Past due 90 days or greater and still accruing	2	20
Past due, total	1,991	739
Loans, current	215,897	229,266
Portfolio, total	$ 217,888	$ 230,005