Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Average recorded investment
Impaired loans with a valuation allowance	$ 72,761	$ 51,526	$ 71,713	$ 55,997
Impaired loans with no related valuation allowance	69,158	59,219	68,097	55,036
Total impaired loans	141,919	110,745	139,810	111,033
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	359	359	750	769
Impaired loans with no related valuation allowance	368	295	688	542
Total impaired loans	727	654	1,438	1,311
Commercial
Average recorded investment
Impaired loans with a valuation allowance	26,587	18,139	24,109	19,271
Impaired loans with no related valuation allowance	27,865	20,078	27,510	19,102
Total impaired loans	54,452	38,217	51,619	38,373
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	93	111	179	276
Impaired loans with no related valuation allowance	201	147	384	242
Total impaired loans	294	258	563	518
Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	27,353	16,503	29,473	19,070
Impaired loans with no related valuation allowance	31,927	27,544	30,701	25,920
Total impaired loans	59,280	44,047	60,174	44,990
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	141	108	319	216
Impaired loans with no related valuation allowance	131	119	231	240
Total impaired loans	272	227	550	456
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	3,730	243	3,174	234
Impaired loans with no related valuation allowance	102	1,994	76	1,051
Total impaired loans	3,832	2,237	3,250	1,285
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	2	4	4
Impaired loans with no related valuation allowance	2	2	4	3
Total impaired loans	4	4	8	7
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	10,011	12,762	10,005	13,183
Impaired loans with no related valuation allowance	7,241	7,075	7,488	6,606
Total impaired loans	17,252	19,837	17,493	19,789
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	97	115	198	232
Impaired loans with no related valuation allowance	29	25	57	48
Total impaired loans	126	140	255	280
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	1,250	1,067	1,213	986
Impaired loans with no related valuation allowance	36	41	226	91
Total impaired loans	1,286	1,108	1,439	1,077
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	2	4	3
Impaired loans with no related valuation allowance	0	0	0	0
Total impaired loans	2	2	4	3
Home equity
Average recorded investment
Impaired loans with a valuation allowance	3,830	2,812	3,739	3,253
Impaired loans with no related valuation allowance	1,987	2,487	2,096	2,266
Total impaired loans	5,817	5,299	5,835	5,519
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	24	21	46	38
Impaired loans with no related valuation allowance	5	2	12	9
Total impaired loans	29	23	58	47
Owner-occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	17,515	12,949	17,522	13,510
Impaired loans with no related valuation allowance	14,110	14,565	12,841	14,967
Total impaired loans	31,625	27,514	30,363	28,477
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	130	81	255	163
Impaired loans with no related valuation allowance	73	81	126	137
Total impaired loans	203	162	381	300
Non-owner occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	9,050	2,246	11,055	3,058
Impaired loans with no related valuation allowance	16,677	9,539	16,073	8,349
Total impaired loans	25,727	11,785	27,128	11,407
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	9	10	54	21
Impaired loans with no related valuation allowance	58	38	105	103
Total impaired loans	67	48	159	124
Vacant land | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	788	1,308	896	2,502
Impaired loans with no related valuation allowance	1,140	3,440	1,787	2,604
Total impaired loans	1,928	4,748	2,683	5,106
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	17	10	32
Impaired loans with no related valuation allowance	0	0	0	0
Total impaired loans	$ 2	$ 17	$ 10	$ 32