Allowance for Loan Losses and Credit Quality of Loans, Past Due Loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 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	$ 41,730	$ 39,485
Nonaccrual	25,708	35,712
Current	6,517,335	6,122,860
Recorded total loans	6,584,773	6,198,057
31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	29,662	28,717
61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	6,658	5,958
Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	5,410	4,810
Commercial [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded total loans	1,317,174	1,242,701
Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded total loans	494,771	507,784
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded total loans	3,028,269	2,786,002
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded total loans	2,234,809	2,149,441
Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Recorded total loans	1,321,695	1,262,614
Originated Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	39,945	37,811
Nonaccrual	23,336	30,077
Current	6,119,801	5,630,075
Recorded total loans	6,183,082	5,697,963
Originated Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	28,383	27,488
Originated Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	6,397	5,870
Originated Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	5,165	4,453
Originated Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	3,413	1,965
Nonaccrual	12,463	18,292
Current	2,825,080	2,528,127
Recorded total loans	2,840,956	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	2,678	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	735	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	0	38
Nonaccrual	202	2,964
Current	753,577	650,568
Recorded total loans	753,779	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	0	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	299	0
Nonaccrual	3,178	7,935
Current	1,533,065	1,343,854
Recorded total loans	1,536,542	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	161	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	138	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	117	0
Nonaccrual	1,043	730
Current	34,386	37,186
Recorded total loans	35,546	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	117	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	493	0
Nonaccrual	2,736	1,803
Current	30,905	30,619
Recorded total loans	34,134	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	493	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	2,504	1,927
Nonaccrual	5,304	4,860
Current	473,147	465,900
Recorded total loans	480,955	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	1,907	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	597	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	30,873	31,543
Nonaccrual	4,886	5,103
Current	2,155,144	2,049,790
Recorded total loans	2,190,903	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	21,975	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	4,995	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	3,903	3,047
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	26,272	25,937
Nonaccrual	2,115	2,145
Current	1,642,664	1,538,593
Recorded total loans	1,671,051	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	18,747	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	4,033	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	3,492	2,499
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	4,082	5,009
Nonaccrual	2,736	2,851
Current	448,081	448,797
Recorded total loans	454,899	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	2,887	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	854	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	341	528
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	519	597
Nonaccrual	35	107
Current	64,399	62,400
Recorded total loans	64,953	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	341	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	108	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	70	20
Originated Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	5,659	4,303
Nonaccrual	5,987	6,682
Current	1,139,577	1,052,158
Recorded total loans	1,151,223	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	3,730	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	667	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	1,262	1,406
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	1,785	1,674
Nonaccrual	2,372	5,635
Current	397,534	492,785
Recorded total loans	401,691	500,094
Acquired Loans [Member] | 31-60 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	1,279	1,229
Acquired Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	261	88
Acquired Loans [Member] | Greater Than 90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	245	357
Acquired Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	354	236
Nonaccrual	671	2,695
Current	186,288	234,687
Recorded total loans	187,313	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	354	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
Nonaccrual	0	0
Current	39,575	49,447
Recorded total loans	39,575	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
Nonaccrual	2	1,891
Current	106,632	135,398
Recorded total loans	106,634	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	354	236
Nonaccrual	669	804
Current	40,081	49,842
Recorded total loans	41,104	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	354	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	438	474
Nonaccrual	270	304
Current	43,198	62,227
Recorded total loans	43,906	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	298	384
Acquired Loans [Member] | Consumer Loans [Member] | 61-90 Days Past Due Accruing [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	35	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	105	30
Acquired Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	39	105
Nonaccrual	22	47
Current	1,157	8,541
Recorded total loans	1,218	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	38	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	0	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	1	0
Acquired Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	391	337
Nonaccrual	225	237
Current	39,256	50,553
Recorded total loans	39,872	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	254	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	34	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	103	30
Acquired Loans [Member] | Consumer Loans [Member] | Direct [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	8	32
Nonaccrual	23	20
Current	2,785	3,133
Recorded total loans	2,816	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	6	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	1	0
Acquired Loans [Member] | Residential Real Estate Mortgages [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total past due accruing	993	964
Nonaccrual	1,431	2,636
Current	168,048	195,871
Recorded total loans	170,472	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	627	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	226	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	$ 140	$ 327