Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 6,367,911	$ 6,198,057
Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,906,314	2,786,002
Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,185,790	2,149,441
Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,275,807	1,262,614
Originated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,906,639	5,697,963
Originated Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,683,795	2,548,384
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,206,997	2,075,697
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,083,874	1,970,912
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	61,679	40,724
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	61,439	64,056
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5	5
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	761,770	653,570
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	708,569	616,829
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	24,829	7,750
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	28,372	28,991
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,375,547	1,351,789
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,318,522	1,288,409
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	31,829	31,053
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	25,196	32,327
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	37,655	37,916
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	32,258	36,762
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,520	25
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,872	1,124
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5	5
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	32,025	32,422
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	24,525	28,912
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,501	1,896
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,999	1,614
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	476,798	472,687
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	476,798	472,687
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	463,897	458,864
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	12,901	13,823
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	476,798	472,687
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	463,897	458,864
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	12,901	13,823
Originated Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,133,251	2,086,436
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,125,814	2,078,286
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,437	8,150
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,615,046	1,566,675
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,610,892	1,562,031
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,154	4,644
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	454,848	456,657
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	451,683	453,278
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,165	3,379
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	63,357	63,104
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	63,239	62,977
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	118	127
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,089,593	1,063,143
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,082,450	1,055,055
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,143	8,088
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,089,593	1,063,143
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,082,450	1,055,055
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,143	8,088
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	461,272	500,094
Acquired Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	222,519	237,618
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	176,582	186,736
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	160,731	175,854
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,894	1,307
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,957	8,370
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		1,205
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	51,179	49,447
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	44,517	48,194
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,719	76
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	943	1,177
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		0
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	125,403	137,289
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	116,214	127,660
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,175	1,231
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,014	7,193
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable		1,205
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,937	50,882
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,937	50,882
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42,499	47,347
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,438	3,535
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,937	50,882
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42,499	47,347
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,438	3,535
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	52,539	63,005
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	52,307	62,671
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	232	334
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,640	8,693
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,603	8,646
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	37	47
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	46,006	51,127
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,823	50,860
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	183	267
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,893	3,185
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,881	3,165
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	12	20
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	186,214	199,471
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	184,198	196,508
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,016	2,963
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	186,214	199,471
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	184,198	196,508
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Residential Mortgage [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 2,016	$ 2,963