Allowance for Probable Loan Losses (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	$ 86,298	$ 83,005
Loans individually evaluated for impairment, Allowance	15,173	4,746
Loans collectively evaluated for impairment, Recorded Investment	4,825,651	4,691,999
Loans collectively evaluated for impairment, Allowance	49,878	53,447
Commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	35,120	32,768
Loans individually evaluated for impairment, Allowance	10,961	1,477
Loans collectively evaluated for impairment, Recorded Investment	841,878	736,342
Loans collectively evaluated for impairment, Allowance	9,715	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	26,490	28,660
Loans individually evaluated for impairment, Allowance	766	539
Loans collectively evaluated for impairment, Recorded Investment	1,116,378	1,119,009
Loans collectively evaluated for impairment, Allowance	10,858	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	16,598	13,945
Loans individually evaluated for impairment, Allowance	3,446	2,730
Loans collectively evaluated for impairment, Recorded Investment	1,713,462	1,659,377
Loans collectively evaluated for impairment, Allowance	18,937	19,150
Commercial real estate: multifamily
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	324	353
Loans collectively evaluated for impairment, Recorded Investment	81,613	82,595
Loans collectively evaluated for impairment, Allowance	623	694
Residential: first lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	4,367	3,656
Loans collectively evaluated for impairment, Recorded Investment	441,481	453,075
Loans collectively evaluated for impairment, Allowance	3,855	4,390
Residential: junior lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,711	1,850
Loans collectively evaluated for impairment, Recorded Investment	379,954	379,886
Loans collectively evaluated for impairment, Allowance	4,047	4,448
Consumer
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,239	1,326
Loans collectively evaluated for impairment, Recorded Investment	66,838	73,188
Loans collectively evaluated for impairment, Allowance	797	1,289
Foreign
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	449	447
Loans collectively evaluated for impairment, Recorded Investment	184,047	188,527
Loans collectively evaluated for impairment, Allowance	$ 1,046	$ 1,140