Allowance for Probable Loan Losses (Details 2) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	$ 56,382	$ 76,171
Loans Individually Evaluated for Impairment, Allowance	1,756	12,221
Loans Collectively Evaluated for Impairment, Recorded Investment	5,866,590	5,603,074
Loans Collectively Evaluated for Impairment, Allowance	63,504	52,607
Commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	31,265	40,175
Loans Individually Evaluated for Impairment, Allowance	1,174	9,112
Loans Collectively Evaluated for Impairment, Recorded Investment	981,126	1,049,311
Loans Collectively Evaluated for Impairment, Allowance	19,351	13,240
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	6,349	10,876
Loans Individually Evaluated for Impairment, Allowance	100	1,890
Loans Collectively Evaluated for Impairment, Recorded Investment	1,648,900	1,404,101
Loans Collectively Evaluated for Impairment, Allowance	14,166	11,065
Commercial real estate: farmland and commercial
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	9,642	14,166
Loans Individually Evaluated for Impairment, Allowance	482	1,219
Loans Collectively Evaluated for Impairment, Recorded Investment	1,943,066	1,887,233
Loans Collectively Evaluated for Impairment, Allowance	19,143	17,464
Commercial real estate: multifamily
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	812	835
Loans Collectively Evaluated for Impairment, Recorded Investment	107,470	115,864
Loans Collectively Evaluated for Impairment, Allowance	805	846
Residential: first lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	5,294	5,840
Loans Collectively Evaluated for Impairment, Recorded Investment	403,982	416,186
Loans Collectively Evaluated for Impairment, Allowance	3,680	3,589
Residential: junior lien
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	1,028	2,895
Loans Collectively Evaluated for Impairment, Recorded Investment	538,396	485,405
Loans Collectively Evaluated for Impairment, Allowance	4,533	4,683
Consumer
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	1,243	1,384
Loans Collectively Evaluated for Impairment, Recorded Investment	57,043	59,753
Loans Collectively Evaluated for Impairment, Allowance	642	660
Foreign
Loan loss allowances, impaired financing receivable, evaluated individually or collectively
Loans Individually Evaluated for Impairment, Recorded Investment	749
Loans Collectively Evaluated for Impairment, Recorded Investment	186,607	185,221
Loans Collectively Evaluated for Impairment, Allowance	$ 1,184	$ 1,060