Loans - Nonperforming Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$ 1,235	$ 1,377
Commercial
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	322	0
Total commercial real estate
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	13
Home equity
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	913	1,364
Nonperforming
Summary of nonperforming loans
Total nonaccrual loans	61,832	63,095
Other real estate owned and repossessed assets	7,719	8,807
Total nonperforming assets	69,551	71,902
Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	20,000	19,691
Nonperforming | Total commercial real estate
Summary of nonperforming loans
Total nonaccrual loans	30,173	29,545
Nonperforming | Real estate construction and land development
Summary of nonperforming loans
Total nonaccrual loans	77	77
Nonperforming | Residential mortgage
Summary of nonperforming loans
Total nonaccrual loans	7,621	8,635
Nonperforming | Consumer installment
Summary of nonperforming loans
Total nonaccrual loans	922	842
Nonperforming | Home equity
Summary of nonperforming loans
Total nonaccrual loans	3,039	4,305
Owner-occupied | Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	19,855	19,070
Non-owner occupied | Commercial
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	0	13
Non-owner occupied | Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	5,489	5,270
Vacant land | Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	$ 4,829	$ 5,205