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	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 24,508	$ 35,641	$ 25,446	$ 34,382
Interest income recognized	194	204	422	484
Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	24,508	34,436	25,274	33,177
Interest income recognized	194	204	422	484
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	3,931	3,126	3,419	2,972
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	3,243	15,278	4,584	14,264
Interest income recognized	1	0	45	74
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	157	18	165	98
Interest income recognized	1	0	1	1
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,549	610	1,564	613
Interest income recognized	10	11	21	22
Originated Loans [Member] \| Commercial Loans [Member] \| Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	890	969	788	973
Interest income recognized	3	6	5	12
Originated Loans [Member] \| Consumer Loans [Member] \| Indirect [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	25	9	16	10
Interest income recognized	1	0	1	0
Originated Loans [Member] \| Consumer Loans [Member] \| Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,205	8,223	8,310	8,093
Interest income recognized	110	120	220	241
Originated Loans [Member] \| Consumer Loans [Member] \| Direct [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	120	0	120	0
Interest income recognized	0	0	0	0
Originated Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,388	6,203	6,308	6,154
Interest income recognized	68	67	129	134
Acquired Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	1,205	172	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	172	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=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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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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