Allowance for Probable Loan Losses (Details 5) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Financing receivable recorded investment
Past due 30-59 days	$ 25,214	$ 19,507
Past due 60-89 days	5,411	28,372
Past due 90 days or greater	88,701	42,357
Past due 90 days or greater and still accruing	11,847	15,033
Past due, total	119,326	90,236
Loans, current	4,932,835	4,684,768
Total loans	5,052,161	4,775,004
Commercial
Financing receivable recorded investment
Past due 30-59 days	4,319	4,393
Past due 60-89 days	1,054	471
Past due 90 days or greater	35,379	3,386
Past due 90 days or greater and still accruing	1,227	2,689
Past due, total	40,752	8,250
Loans, current	977,402	760,860
Total loans	1,018,154	769,110
Commercial real estate: other construction and land development
Financing receivable recorded investment
Past due 30-59 days	1,916	1,107
Past due 60-89 days	292	2,300
Past due 90 days or greater	32,593	24,225
Past due 90 days or greater and still accruing	38	497
Past due, total	34,801	27,632
Loans, current	1,084,541	1,120,037
Total loans	1,119,342	1,147,669
Commercial real estate: farmland and commercial
Financing receivable recorded investment
Past due 30-59 days	7,436	3,127
Past due 60-89 days	297	21,272
Past due 90 days or greater	9,122	2,310
Past due 90 days or greater and still accruing	1,728	929
Past due, total	16,855	26,709
Loans, current	1,706,101	1,646,613
Total loans	1,722,956	1,673,322
Commercial real estate: multifamily
Financing receivable recorded investment
Past due 30-59 days	418	685
Past due 90 days or greater	314	353
Past due, total	732	1,038
Loans, current	99,180	81,910
Total loans	99,912	82,948
Residential: first lien
Financing receivable recorded investment
Past due 30-59 days	6,538	4,305
Past due 60-89 days	3,060	2,510
Past due 90 days or greater	8,612	10,645
Past due 90 days or greater and still accruing	7,751	9,657
Past due, total	18,210	17,460
Loans, current	425,679	439,271
Total loans	443,889	456,731
Residential: junior lien
Financing receivable recorded investment
Past due 30-59 days	1,060	2,035
Past due 60-89 days	175	410
Past due 90 days or greater	1,758	259
Past due 90 days or greater and still accruing	216	115
Past due, total	2,993	2,704
Loans, current	390,444	379,032
Total loans	393,437	381,736
Consumer
Financing receivable recorded investment
Past due 30-59 days	1,615	1,598
Past due 60-89 days	385	404
Past due 90 days or greater	708	915
Past due 90 days or greater and still accruing	685	882
Past due, total	2,708	2,917
Loans, current	64,714	71,597
Total loans	67,422	74,514
Foreign
Financing receivable recorded investment
Past due 30-59 days	1,912	2,257
Past due 60-89 days	148	1,005
Past due 90 days or greater	215	264
Past due 90 days or greater and still accruing	202	264
Past due, total	2,275	3,526
Loans, current	184,774	185,448
Total loans	$ 187,049	$ 188,974