Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Credit Quality by Loan Class [Abstract]
Net loans	$ 6,859,063	$ 6,584,773
Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,317,746	2,234,809
Residential Real Estate Mortgage Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,350,761	1,321,695
Originated Loans [Member]
Credit Quality by Loan Class [Abstract]
Net loans	6,501,074	6,183,082
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,547,091
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,431,877
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	60,873
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	53,941
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Doubtful [Member]
Credit Quality by Loan Class [Abstract]
Net loans	400
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Credit Quality by Loan Class [Abstract]
Net loans	836,387
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	773,097
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	46,153
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	16,737
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Doubtful [Member]
Credit Quality by Loan Class [Abstract]
Net loans	400
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,710,704
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,658,780
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	14,720
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	37,204
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Doubtful [Member]
Credit Quality by Loan Class [Abstract]
Net loans	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,360,001
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,245,016
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		63,336
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		51,649
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Credit Quality by Loan Class [Abstract]
Net loans		753,779
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		708,567
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		30,337
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		14,875
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,536,542
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,481,926
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		28,264
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		26,352
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Credit Quality by Loan Class [Abstract]
Net loans		35,546
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		31,142
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,294
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,110
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans		34,134
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		23,381
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,441
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		8,312
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	481,249	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	469,660	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	11,589	12,057
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Credit Quality by Loan Class [Abstract]
Net loans	481,249	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	469,660	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	11,589	12,057
Originated Loans [Member] | Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,280,881	2,190,903
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,274,020	2,182,114
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	6,861	8,789
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,252,565
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,249,848
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,717
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans	520,698
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	517,660
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	3,038
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member]
Credit Quality by Loan Class [Abstract]
Net loans	507,618
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	506,512
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,106
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,671,051
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,665,444
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		5,607
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Credit Quality by Loan Class [Abstract]
Net loans		454,899
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		451,822
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		3,077
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans		64,953
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		64,848
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		105
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,191,853	1,151,223
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,186,217	1,143,974
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	5,636	7,249
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,191,853	1,151,223
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,186,217	1,143,974
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	5,636	7,249
Acquired Loans [Member]
Credit Quality by Loan Class [Abstract]
Net loans	357,989	401,691
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans	124,105
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	117,807
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	5,583
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	715
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Credit Quality by Loan Class [Abstract]
Net loans	34,054
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	28,989
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	5,019
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	46
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Credit Quality by Loan Class [Abstract]
Net loans	90,051
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	88,818
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	564
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	669
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Credit Quality by Loan Class [Abstract]
Net loans		146,209
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		141,073
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		923
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		4,213
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Credit Quality by Loan Class [Abstract]
Net loans		39,575
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		37,825
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		425
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,325
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans		106,634
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans		103,248
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans		498
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,888
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	38,111	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	35,691	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,420	2,868
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Credit Quality by Loan Class [Abstract]
Net loans	38,111	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	35,691	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,420	2,868
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	36,865	43,906
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	36,537	43,531
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	328	375
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Credit Quality by Loan Class [Abstract]
Net loans	278
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	264
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	14
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans	36,587	2,816
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	36,273
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	314
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,218
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,195
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		23
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Credit Quality by Loan Class [Abstract]
Net loans		39,872
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		39,544
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		328
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,816
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		2,792
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans		24
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	158,908	170,472
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	157,296	168,901
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,612	1,571
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member]
Credit Quality by Loan Class [Abstract]
Net loans	158,908	170,472
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	157,296	168,901
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Residential Real Estate Mortgage [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	$ 1,612	$ 1,571