Allowance for Probable Loan Losses (Details 3) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 116,956	$ 118,505
Commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	25,931	26,819
Commercial real estate: other construction and land development
Loan loss allowances, financing receivable past due
Non-accrual loans, total	64,408	54,336
Commercial real estate: farmland and commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	24,301	34,910
Commercial real estate: multifamily
Loan loss allowances, financing receivable past due
Non-accrual loans, total	397	411
Residential: first lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	1,722	1,848
Residential: junior lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	155	135
Consumer
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 42	$ 46