Allowance for Probable Loan Losses (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	$ 76,263	$ 75,893
Loans individually evaluated for impairment, Allowance	20,942	16,002
Loans collectively evaluated for impairment, Recorded Investment	5,210,237	5,123,342
Loans collectively evaluated for impairment, Allowance	49,466	54,159
Commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	35,539	34,183
Loans individually evaluated for impairment, Allowance	17,424	12,234
Loans collectively evaluated for impairment, Recorded Investment	1,059,024	1,008,459
Loans collectively evaluated for impairment, Allowance	10,499	10,199
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	13,558	13,976
Loans individually evaluated for impairment, Allowance	852	852
Loans collectively evaluated for impairment, Recorded Investment	1,265,445	1,194,532
Loans collectively evaluated for impairment, Allowance	12,623	11,689
Commercial real estate: farmland and commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	15,607	16,038
Loans individually evaluated for impairment, Allowance	2,666	2,916
Loans collectively evaluated for impairment, Recorded Investment	1,706,316	1,734,001
Loans collectively evaluated for impairment, Allowance	16,268	21,551
Commercial real estate: multifamily
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	280	295
Loans collectively evaluated for impairment, Recorded Investment	107,826	101,803
Loans collectively evaluated for impairment, Allowance	819	776
Residential: first lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	6,273	6,153
Loans collectively evaluated for impairment, Recorded Investment	414,736	432,309
Loans collectively evaluated for impairment, Allowance	3,524	3,812
Residential: junior lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	3,123	3,206
Loans collectively evaluated for impairment, Recorded Investment	416,033	406,024
Loans collectively evaluated for impairment, Allowance	3,968	4,249
Consumer
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,453	1,606
Loans collectively evaluated for impairment, Recorded Investment	61,977	64,808
Loans collectively evaluated for impairment, Allowance	748	750
Foreign
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	430	436
Loans collectively evaluated for impairment, Recorded Investment	178,880	181,406
Loans collectively evaluated for impairment, Allowance	$ 1,017	$ 1,133