Loans - Nonperforming Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	$ 1,192	$ 1,377
Commercial
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	632	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	47	13
Real estate construction and land development
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	38	0
Home equity
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	475	1,364
Nonperforming
Summary of nonperforming loans
Total nonaccrual loans	96,673	63,095
Other real estate owned and repossessed assets	6,584	8,807
Total nonperforming assets	103,257	71,902
Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	25,328	19,691
Nonperforming | Total commercial real estate
Summary of nonperforming loans
Total nonaccrual loans	28,638	29,545
Nonperforming | Real estate construction and land development
Summary of nonperforming loans
Total nonaccrual loans	28,477	77
Nonperforming | Residential mortgage
Summary of nonperforming loans
Total nonaccrual loans	9,611	8,635
Nonperforming | Consumer installment
Summary of nonperforming loans
Total nonaccrual loans	1,350	842
Nonperforming | Home equity
Summary of nonperforming loans
Total nonaccrual loans	3,269	4,305
Owner-occupied | Commercial
Summary of nonperforming loans
Total accruing loans contractually past due 90 days or more as to interest or principal payments	47	0
Owner-occupied | Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	14,936	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	8,991	5,270
Vacant land | Nonperforming | Commercial
Summary of nonperforming loans
Total nonaccrual loans	$ 4,711	$ 5,205