Allowance for Probable Loan Losses (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	$ 78,265	$ 136,305
Loans individually evaluated for impairment, Allowance	18,631	27,252
Loans collectively evaluated for impairment, Recorded Investment	4,800,057	4,917,170
Loans collectively evaluated for impairment, Allowance	51,747	56,940
Commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	28,053	27,603
Loans individually evaluated for impairment, Allowance	15,098	14,402
Loans collectively evaluated for impairment, Recorded Investment	780,188	746,213
Loans collectively evaluated for impairment, Allowance	9,590	12,215
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	25,716	60,428
Loans individually evaluated for impairment, Allowance	568	3,073
Loans collectively evaluated for impairment, Recorded Investment	1,184,775	1,212,961
Loans collectively evaluated for impairment, Allowance	12,674	16,867
Commercial real estate: farmland and commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	18,328	42,231
Loans individually evaluated for impairment, Allowance	2,942	9,754
Loans collectively evaluated for impairment, Recorded Investment	1,604,725	1,622,456
Loans collectively evaluated for impairment, Allowance	17,609	14,473
Commercial real estate: multifamily
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	382	411
Loans collectively evaluated for impairment, Recorded Investment	101,594	121,188
Loans collectively evaluated for impairment, Allowance	803	1,003
Residential: first lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	2,752	2,290
Loans individually evaluated for impairment, Allowance	23	23
Loans collectively evaluated for impairment, Recorded Investment	459,751	493,432
Loans collectively evaluated for impairment, Allowance	3,964	4,539
Residential: junior lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,910	1,962
Loans collectively evaluated for impairment, Recorded Investment	377,899	398,186
Loans collectively evaluated for impairment, Allowance	4,410	4,760
Consumer
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	1,079	1,334
Loans collectively evaluated for impairment, Recorded Investment	82,120	92,775
Loans collectively evaluated for impairment, Allowance	1,476	1,724
Foreign
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans individually evaluated for impairment, Recorded Investment	45	46
Loans collectively evaluated for impairment, Recorded Investment	209,005	229,959
Loans collectively evaluated for impairment, Allowance	$ 1,221	$ 1,359