Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Average recorded investment
Impaired loans with a valuation allowance	$ 70,665	$ 60,468
Impaired loans with no related valuation allowance	67,036	50,853
Total impaired loans	137,701	111,321
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	391	410
Impaired loans with no related valuation allowance	320	247
Total impaired loans	711	657
Commercial
Average recorded investment
Impaired loans with a valuation allowance	21,633	20,402
Impaired loans with no related valuation allowance	27,154	18,126
Total impaired loans	48,787	38,528
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	86	165
Impaired loans with no related valuation allowance	183	95
Total impaired loans	269	260
Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	31,593	21,637
Impaired loans with no related valuation allowance	29,474	24,296
Total impaired loans	61,067	45,933
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	178	108
Impaired loans with no related valuation allowance	100	121
Total impaired loans	278	229
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	2,618	225
Impaired loans with no related valuation allowance	49	107
Total impaired loans	2,667	332
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	2
Impaired loans with no related valuation allowance	2	1
Total impaired loans	4	3
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	9,999	13,604
Impaired loans with no related valuation allowance	7,736	6,138
Total impaired loans	17,735	19,742
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	101	117
Impaired loans with no related valuation allowance	28	23
Total impaired loans	129	140
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	1,175	906
Impaired loans with no related valuation allowance	417	140
Total impaired loans	1,592	1,046
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	1
Impaired loans with no related valuation allowance	0	0
Total impaired loans	2	1
Home equity
Average recorded investment
Impaired loans with a valuation allowance	3,647	3,694
Impaired loans with no related valuation allowance	2,206	2,046
Total impaired loans	5,853	5,740
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	22	17
Impaired loans with no related valuation allowance	7	7
Total impaired loans	29	24
Owner-occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	17,528	14,072
Impaired loans with no related valuation allowance	11,571	15,369
Total impaired loans	29,099	29,441
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	125	82
Impaired loans with no related valuation allowance	53	56
Total impaired loans	178	138
Non-owner occupied | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	13,061	3,870
Impaired loans with no related valuation allowance	15,469	7,158
Total impaired loans	28,530	11,028
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	45	11
Impaired loans with no related valuation allowance	47	65
Total impaired loans	92	76
Vacant land | Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	1,004	3,695
Impaired loans with no related valuation allowance	2,434	1,769
Total impaired loans	3,438	5,464
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	8	15
Impaired loans with no related valuation allowance	0	0
Total impaired loans	$ 8	$ 15