Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Net Loans	$ 6,584,773	$ 6,198,057
Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,317,174	1,242,701
Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	494,771	507,784
Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,234,809	2,149,441
Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,321,695	1,262,614
Originated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	6,183,082	5,697,963
Originated Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,360,001	2,075,697
Originated Loans [Member] | Commercial Credit Exposure [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,245,016	1,970,912
Originated Loans [Member] | Commercial Credit Exposure [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	63,336	40,724
Originated Loans [Member] | Commercial Credit Exposure [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	51,649	64,056
Originated Loans [Member] | Commercial Credit Exposure [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		5
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	753,779	653,570
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	708,567	616,829
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	30,337	7,750
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	14,875	28,991
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,536,542	1,351,789
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,481,926	1,288,409
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	28,264	31,053
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	26,352	32,327
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	35,546	37,916
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	31,142	36,762
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,294	25
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,110	1,124
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		5
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	34,134	32,422
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	23,381	28,912
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,441	1,896
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	8,312	1,614
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		0
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	480,955	472,687
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	468,898	458,864
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	12,057	13,823
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	480,955	472,687
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	468,898	458,864
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	12,057	13,823
Originated Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,190,903	2,086,436
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,182,114	2,078,286
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	8,789	8,150
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,671,051	1,566,675
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,665,444	1,562,031
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	5,607	4,644
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	454,899	456,657
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	451,822	453,278
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	3,077	3,379
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	64,953	63,104
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	64,848	62,977
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	105	127
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,151,223	1,063,143
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,143,974	1,055,055
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	7,249	8,088
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,151,223	1,063,143
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,143,974	1,055,055
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	7,249	8,088
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	401,691	500,094
Acquired Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	146,209	186,736
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	141,073	175,854
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	923	1,307
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	4,213	8,370
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		1,205
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	39,575	49,447
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	37,825	48,194
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	425	76
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,325	1,177
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	106,634	137,289
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	103,248	127,660
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	498	1,231
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,888	7,193
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans		1,205
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	41,104	50,882
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	38,236	47,347
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,868	3,535
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	41,104	50,882
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	38,236	47,347
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,868	3,535
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	43,906	63,005
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	43,531	62,671
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	375	334
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,218	8,693
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,195	8,646
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	23	47
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	39,872	51,127
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	39,544	50,860
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	328	267
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,816	3,185
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	2,792	3,165
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	24	20
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	170,472	199,471
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	168,901	196,508
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	1,571	2,963
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	170,472	199,471
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	168,901	196,508
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Net Loans	$ 1,571	$ 2,963