Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Average recorded investment
Impaired loans with a valuation allowance	$ 56,408	$ 65,165	$ 56,134	$ 65,977
Impaired loans with no related valuation allowance	68,785	42,653	59,619	40,864
Total impaired loans	125,193	107,818	115,753	106,841
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	323	588	1,092	1,764
Impaired loans with no related valuation allowance	313	123	855	427
Total impaired loans	636	711	1,947	2,191
Commercial
Average recorded investment
Impaired loans with a valuation allowance	13,945	25,628	17,495	25,278
Impaired loans with no related valuation allowance	24,114	10,120	20,773	10,142
Total impaired loans	38,059	35,748	38,268	35,420
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	67	222	343	647
Impaired loans with no related valuation allowance	123	14	365	92
Total impaired loans	190	236	708	739
Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	17,263	18,300	18,468	19,120
Impaired loans with no related valuation allowance	29,481	25,435	27,107	24,697
Total impaired loans	46,744	43,735	45,575	43,817
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	114	197	330	602
Impaired loans with no related valuation allowance	149	101	389	304
Total impaired loans	263	298	719	906
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	9,647	175	3,372	159
Impaired loans with no related valuation allowance	3,857	71	1,986	86
Total impaired loans	13,504	246	5,358	245
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	3	6	8
Impaired loans with no related valuation allowance	2	0	5	0
Total impaired loans	4	3	11	8
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	11,620	15,945	12,662	16,529
Impaired loans with no related valuation allowance	8,605	5,144	7,272	4,511
Total impaired loans	20,225	21,089	19,934	21,040
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	117	144	349	446
Impaired loans with no related valuation allowance	31	8	79	25
Total impaired loans	148	152	428	471
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	911	748	961	737
Impaired loans with no related valuation allowance	537	244	240	201
Total impaired loans	1,448	992	1,201	938
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	3	1	6	3
Impaired loans with no related valuation allowance	0	0	0	0
Total impaired loans	3	1	6	3
Home equity
Average recorded investment
Impaired loans with a valuation allowance	3,022	4,369	3,176	4,154
Impaired loans with no related valuation allowance	2,191	1,639	2,241	1,227
Total impaired loans	5,213	6,008	5,417	5,381
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	20	21	58	58
Impaired loans with no related valuation allowance	8	0	17	6
Total impaired loans	28	21	75	64
Owner-occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	11,977	13,401	12,999	14,083
Impaired loans with no related valuation allowance	13,831	13,009	14,588	10,862
Total impaired loans	25,808	26,410	27,587	24,945
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	94	155	257	459
Impaired loans with no related valuation allowance	68	1	205	13
Total impaired loans	162	156	462	472
Non-owner occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	3,697	2,457	3,271	2,939
Impaired loans with no related valuation allowance	12,776	8,942	9,825	9,487
Total impaired loans	16,473	11,399	13,096	12,426
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	13	17	34	68
Impaired loans with no related valuation allowance	81	88	184	255
Total impaired loans	94	105	218	323
Vacant land | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	1,589	2,442	2,198	2,098
Impaired loans with no related valuation allowance	2,874	3,484	2,694	4,348
Total impaired loans	4,463	5,926	4,892	6,446
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	7	25	39	75
Impaired loans with no related valuation allowance	0	12	0	36
Total impaired loans	$ 7	$ 37	$ 39	$ 111