Allowance for Probable Loan Losses (Non-accrual Basis By Loan Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 29,570	$ 37,245
Commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	20,152	22,369
Commercial Real Estate: Other Construction and Land Development
Loan loss allowances, financing receivable past due
Non-accrual loans, total	2,428	4,776
Commercial Real Estate: Farmland & Commercial
Loan loss allowances, financing receivable past due
Non-accrual loans, total	5,966	8,314
Commercial Real Estate: Multifamily
Loan loss allowances, financing receivable past due
Non-accrual loans, total	496	552
Residential First Lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	464	655
Residential Junior Lien
Loan loss allowances, financing receivable past due
Non-accrual loans, total	12	166
Consumer
Loan loss allowances, financing receivable past due
Non-accrual loans, total	$ 52	26
Foreign
Loan loss allowances, financing receivable past due
Non-accrual loans, total		$ 387