Loans - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Average recorded investment
Impaired loans with a valuation allowance	$ 65,165	$ 27,018	$ 65,977	$ 31,442
Impaired loans with no related valuation allowance	42,653	80,944	40,864	84,426
Total impaired loans	107,818	107,962	106,841	115,868
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	588	321	1,764	987
Impaired loans with no related valuation allowance	123	689	427	1,976
Total impaired loans	711	1,010	2,191	2,963
Commercial
Average recorded investment
Impaired loans with a valuation allowance	25,628	4,350	25,278	6,256
Impaired loans with no related valuation allowance	10,120	31,717	10,142	31,874
Total impaired loans	35,748	36,067	35,420	38,130
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	222	0	647	0
Impaired loans with no related valuation allowance	14	399	92	986
Total impaired loans	236	399	739	986
Commercial real estate
Average recorded investment
Impaired loans with a valuation allowance	18,300	2,430	19,120	4,461
Impaired loans with no related valuation allowance	25,435	41,205	24,697	44,207
Total impaired loans	43,735	43,635	43,817	48,668
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	197	0	602	0
Impaired loans with no related valuation allowance	101	285	304	977
Total impaired loans	298	285	906	977
Real estate construction and land development
Average recorded investment
Impaired loans with a valuation allowance	175	0	159	0
Impaired loans with no related valuation allowance	71	385	86	720
Total impaired loans	246	385	245	720
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	3	0	8	0
Impaired loans with no related valuation allowance	0	5	0	13
Total impaired loans	3	5	8	13
Residential mortgage
Average recorded investment
Impaired loans with a valuation allowance	15,945	20,238	16,529	20,725
Impaired loans with no related valuation allowance	5,144	5,173	4,511	5,139
Total impaired loans	21,089	25,411	21,040	25,864
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	144	321	446	987
Impaired loans with no related valuation allowance	8	0	25	0
Total impaired loans	152	321	471	987
Consumer installment
Average recorded investment
Impaired loans with a valuation allowance	748	0	737	0
Impaired loans with no related valuation allowance	244	340	201	320
Total impaired loans	992	340	938	320
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	1	0	3	0
Impaired loans with no related valuation allowance	0	0	0	0
Total impaired loans	1	0	3	0
Home equity
Average recorded investment
Impaired loans with a valuation allowance	4,369	0	4,154	0
Impaired loans with no related valuation allowance	1,639	2,124	1,227	2,166
Total impaired loans	6,008	2,124	5,381	2,166
Interest income recognized while on impaired status
Impaired loans with a valuation allowance	21	0	58	0
Impaired loans with no related valuation allowance	0	0	6	0
Total impaired loans	$ 21	$ 0	$ 64	$ 0