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, 2017	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Impaired [Line Items]
Average recorded investment	$ 23,238	$ 30,132	$ 32,470
Interest income recognized accrual	924	970	895
Originated Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	23,145	28,927	24,691
Interest income recognized accrual	924	970	895
Originated Loans [Member] \| Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,183	14,498	12,493
Interest income recognized accrual	171	221	302
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	1,841	6,217	2,219
Interest income recognized accrual	0	0	71
Originated Loans [Member] \| Commercial Loans [Member] \| Commercial Real Estate [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	3,534	5,828	8,538
Interest income recognized accrual	115	167	164
Originated Loans [Member] \| Commercial Loans [Member] \| Agricultural [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	224	715	148
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	1,709	908	628
Interest income recognized accrual	43	44	45
Originated Loans [Member] \| Commercial Loans [Member] \| Business Banking [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	875	830	960
Interest income recognized accrual	12	9	21
Originated Loans [Member] \| Consumer Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,439	8,286	7,070
Interest income recognized accrual	457	480	374
Originated Loans [Member] \| Consumer Loans [Member] \| Indirect [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	35	8	0
Interest income recognized accrual	3	0	0
Originated Loans [Member] \| Consumer Loans [Member] \| Home Equity [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	8,226	8,278	7,070
Interest income recognized accrual	446	480	374
Originated Loans [Member] \| Consumer Loans [Member] \| Direct [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	178	0	0
Interest income recognized accrual	8	0	0
Originated Loans [Member] \| Residential Real Estate Mortgages [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	6,523	6,143	5,128
Interest income recognized accrual	296	269	219
Acquired Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	93	1,205	7,779
Interest income recognized accrual	0	0	0
Acquired Loans [Member] \| Commercial Loans [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	93	1,205	7,779
Interest income recognized accrual	0	0	0
Acquired Loans [Member] \| Commercial Loans [Member] \| Commercial [Member]
Financing Receivable, Impaired [Line Items]
Average recorded investment	0	0	2,045
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	93	1,205	5,734
Interest income recognized accrual	$ 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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