Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Aging [Abstract]
Minimum number of days past due for nonaccrual loan status	90 days
Total Past Due Accruing	$ 33,650	$ 39,485
Non-Accrual	32,674	35,712
Current	6,205,979	6,122,860
Recorded Total Loans	6,272,303	6,198,057
31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	26,254	28,717
61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	5,004	5,958
Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,392	4,810
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded Total Loans	2,824,936	2,786,002
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded Total Loans	2,171,593	2,149,441
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded Total Loans	1,275,774	1,262,614
Originated Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	31,645	37,811
Non-Accrual	28,360	30,077
Current	5,734,172	5,630,075
Recorded Total Loans	5,794,177	5,697,963
Originated Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	24,275	27,488
Originated Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	4,987	5,870
Originated Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,383	4,453
Originated Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	3,971	1,965
Non-Accrual	14,651	18,292
Current	2,578,293	2,528,127
Recorded Total Loans	2,596,915	2,548,384
Originated Loans [Member] | Commercial Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	3,543	1,642
Originated Loans [Member] | Commercial Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	428	323
Originated Loans [Member] | Commercial Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	292	38
Non-Accrual	4,913	2,964
Current	702,383	650,568
Recorded Total Loans	707,588	653,570
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	292	33
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	5
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	286	0
Non-Accrual	2,516	7,935
Current	1,346,470	1,343,854
Recorded Total Loans	1,349,272	1,351,789
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	286	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Non-Accrual	685	730
Current	36,052	37,186
Recorded Total Loans	36,737	37,916
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Non-Accrual	1,771	1,803
Current	30,314	30,619
Recorded Total Loans	32,085	32,422
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	3,393	1,927
Non-Accrual	4,766	4,860
Current	463,074	465,900
Recorded Total Loans	471,233	472,687
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,965	1,609
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	428	318
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Originated Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	24,908	31,543
Non-Accrual	5,124	5,103
Current	2,084,709	2,049,790
Recorded Total Loans	2,114,741	2,086,436
Originated Loans [Member] | Consumer Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	18,288	23,121
Originated Loans [Member] | Consumer Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	4,237	5,375
Originated Loans [Member] | Consumer Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,383	3,047
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	21,181	25,937
Non-Accrual	2,135	2,145
Current	1,575,393	1,538,593
Recorded Total Loans	1,598,709	1,566,675
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	15,407	19,253
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	3,552	4,185
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,222	2,499
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	3,307	5,009
Non-Accrual	2,926	2,851
Current	447,902	448,797
Recorded Total Loans	454,135	456,657
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,635	3,416
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	614	1,065
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	58	528
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	420	597
Non-Accrual	63	107
Current	61,414	62,400
Recorded Total Loans	61,897	63,104
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	246	452
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	71	125
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	103	20
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,766	4,303
Non-Accrual	8,585	6,682
Current	1,071,170	1,052,158
Recorded Total Loans	1,082,521	1,063,143
Originated Loans [Member] | Residential Real Estate Mortgages [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,444	2,725
Originated Loans [Member] | Residential Real Estate Mortgages [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	322	172
Originated Loans [Member] | Residential Real Estate Mortgages [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	1,406
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2,005	1,674
Non-Accrual	4,314	5,635
Current	471,807	492,785
Recorded Total Loans	478,126	500,094
Acquired Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	1,979	1,229
Acquired Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	17	88
Acquired Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	9	357
Acquired Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	441	236
Non-Accrual	1,689	2,695
Current	225,891	234,687
Recorded Total Loans	228,021	237,618
Acquired Loans [Member] | Commercial Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	441	236
Acquired Loans [Member] | Commercial Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Non-Accrual	0	0
Current	45,908	49,447
Recorded Total Loans	45,908	49,447
Acquired Loans [Member] | Commercial Loans [Member] | Commercial [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Non-Accrual	889	1,891
Current	132,611	135,398
Recorded Total Loans	133,500	137,289
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	441	236
Non-Accrual	800	804
Current	47,372	49,842
Recorded Total Loans	48,613	50,882
Acquired Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	441	236
Acquired Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Business Banking [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	249	474
Non-Accrual	248	304
Current	56,355	62,227
Recorded Total Loans	56,852	63,005
Acquired Loans [Member] | Consumer Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	238	384
Acquired Loans [Member] | Consumer Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	2	60
Acquired Loans [Member] | Consumer Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	9	30
Acquired Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	47	105
Non-Accrual	39	47
Current	5,713	8,541
Recorded Total Loans	5,799	8,693
Acquired Loans [Member] | Consumer Loans [Member] | Indirect [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	37	100
Acquired Loans [Member] | Consumer Loans [Member] | Indirect [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	1	5
Acquired Loans [Member] | Consumer Loans [Member] | Indirect [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	9	0
Acquired Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	177	337
Non-Accrual	196	237
Current	47,716	50,553
Recorded Total Loans	48,089	51,127
Acquired Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	177	254
Acquired Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	53
Acquired Loans [Member] | Consumer Loans [Member] | Home Equity [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	30
Acquired Loans [Member] | Consumer Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	25	32
Non-Accrual	13	20
Current	2,926	3,133
Recorded Total Loans	2,964	3,185
Acquired Loans [Member] | Consumer Loans [Member] | Direct [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	24	30
Acquired Loans [Member] | Consumer Loans [Member] | Direct [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	1	2
Acquired Loans [Member] | Consumer Loans [Member] | Direct [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	0	0
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	1,315	964
Non-Accrual	2,377	2,636
Current	189,561	195,871
Recorded Total Loans	193,253	199,471
Acquired Loans [Member] | Residential Real Estate Mortgages [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	1,300	609
Acquired Loans [Member] | Residential Real Estate Mortgages [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	15	28
Acquired Loans [Member] | Residential Real Estate Mortgages [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Past Due Accruing	$ 0	$ 327