Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Average recorded investment
Impaired loans with a valuation allowance	$ 60,468	$ 68,157
Impaired loans with no related valuation allowance	50,853	37,754
Total impaired loans	111,321	105,911
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	410	606
Impaired loans with no related valuation allowance	247	142
Total impaired loans	657	748
Commercial
Average recorded investment
Impaired loans with a valuation allowance	20,402	25,712
Impaired loans with no related valuation allowance	18,126	9,297
Total impaired loans	38,528	35,009
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	165	224
Impaired loans with no related valuation allowance	95	30
Total impaired loans	260	254
Total commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	21,637	20,035
Impaired loans with no related valuation allowance	24,296	23,473
Total impaired loans	45,933	43,508
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	108	203
Impaired loans with no related valuation allowance	121	103
Total impaired loans	229	306
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	225	161
Impaired loans with no related valuation allowance	107	81
Total impaired loans	332	242
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	2	2
Impaired loans with no related valuation allowance	1	0
Total impaired loans	3	2
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	13,604	17,398
Impaired loans with no related valuation allowance	6,138	3,808
Total impaired loans	19,742	21,206
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	117	155
Impaired loans with no related valuation allowance	23	8
Total impaired loans	140	163
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	906	780
Impaired loans with no related valuation allowance	140	215
Total impaired loans	1,046	995
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	1	1
Impaired loans with no related valuation allowance	0	0
Total impaired loans	1	1
Home equity
Average recorded investment
Impaired loans with a valuation allowance	3,694	4,071
Impaired loans with no related valuation allowance	2,046	880
Total impaired loans	5,740	4,951
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	17	21
Impaired loans with no related valuation allowance	7	1
Total impaired loans	24	22
Owner-occupied | Commercial
Average recorded investment
Impaired loans with a valuation allowance	14,072	14,659
Impaired loans with no related valuation allowance	15,369	9,866
Total impaired loans	29,441	24,525
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	82	154
Impaired loans with no related valuation allowance	56	6
Total impaired loans	138	160
Non-owner occupied | Commercial
Average recorded investment
Impaired loans with a valuation allowance	3,870	3,388
Impaired loans with no related valuation allowance	7,158	9,131
Total impaired loans	11,028	12,519
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	11	24
Impaired loans with no related valuation allowance	65	85
Total impaired loans	76	109
Vacant land | Commercial
Average recorded investment
Impaired loans with a valuation allowance	3,695	1,988
Impaired loans with no related valuation allowance	1,769	4,476
Total impaired loans	5,464	6,464
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	15	25
Impaired loans with no related valuation allowance	0	12
Total impaired loans	$ 15	$ 37