Allowance for Probable Loan Losses (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Financing receivable recorded investment
Past due 30-59 days	$ 18,901	$ 19,507
Past due 60-89 days	43,841	28,372
Past due 90 days or greater	53,600	42,357
Past due 90 days or greater and still accruing	25,606	15,033
Past due, total	116,342	90,236
Loans, current	4,710,167	4,684,768
Total loans	4,826,509	4,775,004
Commercial
Financing receivable recorded investment
Past due 30-59 days	4,024	4,393
Past due 60-89 days	25,758	471
Past due 90 days or greater	4,457	3,386
Past due 90 days or greater and still accruing	3,762	2,689
Past due, total	34,239	8,250
Loans, current	834,718	760,860
Total loans	868,957	769,110
Commercial real estate: other construction and land development
Financing receivable recorded investment
Past due 30-59 days	556	1,107
Past due 60-89 days	14,352	2,300
Past due 90 days or greater	30,668	24,225
Past due 90 days or greater and still accruing	7,910	497
Past due, total	45,576	27,632
Loans, current	1,039,930	1,120,037
Total loans	1,085,506	1,147,669
Commercial real estate: farmland and commercial
Financing receivable recorded investment
Past due 30-59 days	6,067	3,127
Past due 60-89 days	2,039	21,272
Past due 90 days or greater	7,767	2,310
Past due 90 days or greater and still accruing	4,491	929
Past due, total	15,873	26,709
Loans, current	1,693,564	1,646,613
Total loans	1,709,437	1,673,322
Commercial real estate: multifamily
Financing receivable recorded investment
Past due 30-59 days	862	685
Past due 90 days or greater	412	353
Past due 90 days or greater and still accruing	73
Past due, total	1,274	1,038
Loans, current	77,580	81,910
Total loans	78,854	82,948
Residential: first lien
Financing receivable recorded investment
Past due 30-59 days	4,093	4,305
Past due 60-89 days	1,232	2,510
Past due 90 days or greater	8,648	10,645
Past due 90 days or greater and still accruing	7,836	9,657
Past due, total	13,973	17,460
Loans, current	436,418	439,271
Total loans	450,391	456,731
Residential: junior lien
Financing receivable recorded investment
Past due 30-59 days	641	2,035
Past due 60-89 days	112	410
Past due 90 days or greater	434	259
Past due 90 days or greater and still accruing	372	115
Past due, total	1,187	2,704
Loans, current	377,510	379,032
Total loans	378,697	381,736
Consumer
Financing receivable recorded investment
Past due 30-59 days	1,702	1,598
Past due 60-89 days	299	404
Past due 90 days or greater	658	915
Past due 90 days or greater and still accruing	627	882
Past due, total	2,659	2,917
Loans, current	67,371	71,597
Total loans	70,030	74,514
Foreign
Financing receivable recorded investment
Past due 30-59 days	956	2,257
Past due 60-89 days	49	1,005
Past due 90 days or greater	556	264
Past due 90 days or greater and still accruing	535	264
Past due, total	1,561	3,526
Loans, current	183,076	185,448
Total loans	$ 184,637	$ 188,974