Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Net loans	$ 6,647,124	$ 6,584,773
Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,266,054	2,234,809
Residential Real Estate Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,333,067	1,321,695
Originated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	6,269,415	6,183,082
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,393,304
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,282,118
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	53,411
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	57,775
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	787,948
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	731,934
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	37,543
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	18,471
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,605,356
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,550,184
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	15,868
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	39,304
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,360,001
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,245,016
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		63,336
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		51,649
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		753,779
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		708,567
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		30,337
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		14,875
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,536,542
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,481,926
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		28,264
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		26,352
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		35,546
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		31,142
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,294
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,110
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		34,134
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		23,381
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,441
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		8,312
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	481,779	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	468,842	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	12,937	12,057
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	481,779	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	468,842	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	12,937	12,057
Originated Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,225,388	2,190,903
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,218,037	2,182,114
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	7,351	8,789
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,240,196
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,237,008
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	3,188
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	513,518
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	510,647
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,871
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	471,674
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	470,382
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,292
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,671,051
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,665,444
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		5,607
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		454,899
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		451,822
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		3,077
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		64,953
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		64,848
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		105
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,168,944	1,151,223
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,163,254	1,143,974
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	5,690	7,249
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,168,944	1,151,223
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,163,254	1,143,974
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	5,690	7,249
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	377,709	401,691
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	130,949
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	126,932
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,553
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,464
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	33,484
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	30,699
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,069
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	716
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	97,465
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	96,233
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	484
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	748
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		146,209
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		141,073
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		923
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		4,213
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		39,575
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		37,825
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		425
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,325
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		106,634
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		103,248
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		498
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,888
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	41,971	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	39,111	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,860	2,868
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	41,971	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	39,111	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	2,860	2,868
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	40,666	43,906
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	40,319	43,531
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	347	375
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	602
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	587
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	15
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	40,064	2,816
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	39,732
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	332
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,218
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		1,195
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		23
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		39,872
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		39,544
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		328
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,816
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		2,792
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans		24
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	164,123	170,472
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	162,448	168,901
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	1,675	1,571
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	164,123	170,472
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	162,448	168,901
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net loans	$ 1,675	$ 1,571