Allowance for Probable Loan Losses (Details 2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	$ 99,026	$ 83,005
Loans individually evaluated for impairment, Allowance	14,997	4,746
Loans collectively evaluated for impairment, Recorded Investment	4,953,135	4,691,999
Loans collectively evaluated for impairment, Allowance	52,832	53,447
Commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	35,231	32,768
Loans individually evaluated for impairment, Allowance	10,741	1,477
Loans collectively evaluated for impairment, Recorded Investment	982,923	736,342
Loans collectively evaluated for impairment, Allowance	10,423	10,155
Commercial real estate: other construction and land development
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	36,304	28,660
Loans individually evaluated for impairment, Allowance	852	539
Loans collectively evaluated for impairment, Recorded Investment	1,083,038	1,119,009
Loans collectively evaluated for impairment, Allowance	10,770	12,181
Commercial real estate: farmland and commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	17,038	13,945
Loans individually evaluated for impairment, Allowance	3,404	2,730
Loans collectively evaluated for impairment, Recorded Investment	1,705,918	1,659,377
Loans collectively evaluated for impairment, Allowance	20,537	19,150
Commercial real estate: multifamily
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	314	353
Loans collectively evaluated for impairment, Recorded Investment	99,598	82,595
Loans collectively evaluated for impairment, Allowance	735	694
Residential: first lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	4,984	3,656
Loans collectively evaluated for impairment, Recorded Investment	438,905	453,075
Loans collectively evaluated for impairment, Allowance	4,064	4,390
Residential: junior lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	3,219	1,850
Loans collectively evaluated for impairment, Recorded Investment	390,218	379,886
Loans collectively evaluated for impairment, Allowance	4,382	4,448
Consumer
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,481	1,326
Loans collectively evaluated for impairment, Recorded Investment	65,941	73,188
Loans collectively evaluated for impairment, Allowance	812	1,289
Foreign
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	455	447
Loans collectively evaluated for impairment, Recorded Investment	186,594	188,527
Loans collectively evaluated for impairment, Allowance	$ 1,109	$ 1,140