Allowance for Probable Loan Losses (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 68,079	$ 71,768
Commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	32,292	31,929
Commercial real estate: other construction and land development
Loan loss allowances, financing receivable past due
Non-accrual loans, total	23,922	26,410
Commercial real estate: farmland and commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	9,636	11,681
Commercial real estate: multifamily
Loan loss allowances, financing receivable past due
Non-accrual loans, total	338	353
Residential: first lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	1,702	1,175
Residential: junior lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	126	175
Consumer
Loan loss allowances, financing receivable past due
Non-accrual loans, total	42	45
Foreign
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 21