Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Credit Quality by Loan Class [Abstract]
Net loans	$ 6,887,262	$ 6,583,639
Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,301,198	2,234,349
Residential Real Estate Mortgage Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,373,487	1,321,021
Originated Loans [Member]
Credit Quality by Loan Class [Abstract]
Net loans	6,546,387	6,181,948
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial, Industrial and Commercial Real Estate [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,572,079
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	2,466,233
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	50,319
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	55,527
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Credit Quality by Loan Class [Abstract]
Net loans	858,940
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	805,333
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	33,557
Originated Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	20,050
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,713,139
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,660,900
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	16,762
Originated Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	35,477
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	486,690	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	474,252	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	12,438	12,057
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Credit Quality by Loan Class [Abstract]
Net loans	486,690	480,955
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	474,252	468,898
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	12,438	12,057
Originated Loans [Member] | Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,267,204	2,190,443
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,259,371	2,181,654
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	7,833	8,789
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,229,597
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,226,283
Originated Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	3,314
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans	516,211
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	513,236
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	2,975
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member]
Credit Quality by Loan Class [Abstract]
Net loans	521,396
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	519,852
Originated Loans [Member] | Consumer Credit Exposure [Member] | Specialty Lending [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,544
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,670,591
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans		1,664,984
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	1,220,414	1,150,549
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,213,077	1,143,300
Originated Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	7,337	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	1,220,414	1,150,549
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	1,213,077	1,143,300
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	7,337	7,249
Acquired Loans [Member]
Credit Quality by Loan Class [Abstract]
Net loans	340,875	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	118,700
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	114,137
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	3,918
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	645
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member]
Credit Quality by Loan Class [Abstract]
Net loans	30,871
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	27,046
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	3,825
Acquired Loans [Member] | Commercial Credit Exposure [Member] | C&I [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member]
Credit Quality by Loan Class [Abstract]
Net loans	87,829
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Pass [Member]
Credit Quality by Loan Class [Abstract]
Net loans	87,091
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Special Mention [Member]
Credit Quality by Loan Class [Abstract]
Net loans	93
Acquired Loans [Member] | Commercial Credit Exposure [Member] | CRE [Member] | Substandard [Member]
Credit Quality by Loan Class [Abstract]
Net loans	645
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	35,108	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	32,098	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	3,010	2,868
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Credit Quality by Loan Class [Abstract]
Net loans	35,108	41,104
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	32,098	38,236
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Credit Quality by Loan Class [Abstract]
Net loans	3,010	2,868
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Credit Quality by Loan Class [Abstract]
Net loans	33,994	43,906
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	33,719	43,531
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	275	375
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member]
Credit Quality by Loan Class [Abstract]
Net loans	103
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	103
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Dealer Finance [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	0
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Credit Quality by Loan Class [Abstract]
Net loans	33,891	2,816
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	33,616
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	275
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	153,073	170,472
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Performing [Member]
Credit Quality by Loan Class [Abstract]
Net loans	151,635	168,901
Acquired Loans [Member] | Residential Real Estate Mortgage Credit Exposure [Member] | Nonperforming [Member]
Credit Quality by Loan Class [Abstract]
Net loans	1,438	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	153,073	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	151,635	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	$ 1,438	$ 1,571