Allowance for Loan Losses and Credit Quality of Loans, Average Recorded Investments on Loans Specifically Evaluated for Impairment and Interest Income Recognized (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 20,936	$ 36,521	$ 23,789	$ 35,116
Interest income recognized	257	251	679	731
Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	20,936	35,316	23,668	33,911
Interest income recognized	257	251	679	731
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,000	3,204	2,393	3,041
Interest income recognized	0	0	0	0
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	2,415	15,799	3,906	14,782
Interest income recognized	48	48	93	122
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	115	85	147	101
Interest income recognized	0	0	1	1
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,505	935	1,545	742
Interest income recognized	11	11	32	33
Originated Loans [Member] \| Commercial Loans [Member] \| Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	955	743	837	882
Interest income recognized	2	0	7	7
Originated Loans [Member] \| Consumer Loans [Member] \| Indirect [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	35	8	22	9
Interest income recognized	1	0	2	0
Originated Loans [Member] \| Consumer Loans [Member] \| Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,159	8,401	8,274	8,207
Interest income recognized	111	116	331	357
Originated Loans [Member] \| Consumer Loans [Member] \| Direct [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	119	0	119	0
Interest income recognized	2	0	2	0
Originated Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,633	6,141	6,425	6,147
Interest income recognized	82	76	211	211
Acquired Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	1,205	121	1,205
Interest income recognized	0	0	0	0
Acquired Loans [Member] \| Commercial Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	1,205	121	1,205
Interest income recognized	$ 0	$ 0	$ 0	$ 0

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Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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