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	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 30,132	$ 32,470	$ 31,059
Interest income recognized accrual	970	895	772
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,217	2,219	1,954
Interest income recognized accrual	0	71	115
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	5,828	8,538	9,679
Interest income recognized accrual	167	164	169
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	715	148	91
Interest income recognized accrual	1	1	1
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	908	628	1,346
Interest income recognized accrual	44	45	46
Originated Loans [Member] \| Commercial Loans [Member] \| Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	830	960	610
Interest income recognized accrual	9	21	55
Originated Loans [Member] \| Consumer Loans [Member] \| Indirect [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8	0	0
Interest income recognized accrual	0	0	0
Originated Loans [Member] \| Consumer Loans [Member] \| Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,278	7,070	5,198
Interest income recognized accrual	480	374	267
Originated Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,143	5,128	3,039
Interest income recognized accrual	269	219	119
Acquired Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	2,045	5,756
Interest income recognized accrual	0	0	0
Acquired Loans [Member] \| Commercial Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,205	5,734	3,386
Interest income recognized accrual	$ 0	$ 0	$ 0

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- Definition

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=66008989&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=66008989&loc=d3e5258-111524

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- Definition

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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