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Allowance for Loan Losses and Credit Quality of Loans, Additional Information on Loans Specifically Evaluated for Impairment (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Allowance for Loan Losses and Credit Quality of Loans [Abstract] |  |
Threshold balance for classified loans to be evaluated individually for impairment | $ 750 |
Total [Abstract] |  |
Recorded investment balance (book) | 21,138 | $ 28,874
Unpaid principal balance (legal) | 28,120 | 31,582
Related allowance | 57 | 1,517
Originated Loans [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 21,035 | 21,912
Unpaid principal balance (legal) | 28,011 | 24,321
Originated Loans [Member] | Commercial Loans [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 5,773 | 7,313
Unpaid principal balance (legal) | 8,848 | 7,970
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 103 | 5,757
Unpaid principal balance (legal) | 109 | 5,940
Total [Abstract] |  |
Related allowance | 57 | 826
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 0 | 1,278
Unpaid principal balance (legal) | 251 | 1,697
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 2,211 | 3,816
Unpaid principal balance (legal) | 3,979 | 3,841
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 76 | 5,553
Unpaid principal balance (legal) | 82 | 5,736
Total [Abstract] |  |
Related allowance | 30 | 735
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 452 | 130
Unpaid principal balance (legal) | 465 | 137
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 27 | 49
Unpaid principal balance (legal) | 27 | 49
Total [Abstract] |  |
Related allowance | 27 | 37
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 2,250 | 1,434
Unpaid principal balance (legal) | 2,423 | 1,567
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 0 | 155
Unpaid principal balance (legal) | 0 | 155
Total [Abstract] |  |
Related allowance | 0 | 54
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 860 | 655
Unpaid principal balance (legal) | 1,730 | 728
Originated Loans [Member] | Consumer Loans [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 8,432 | 8,488
Unpaid principal balance (legal) | 10,383 | 9,445
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 131 | 5
Unpaid principal balance (legal) | 143 | 16
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 8,027 | 8,483
Unpaid principal balance (legal) | 9,966 | 9,429
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 274 | 0
Unpaid principal balance (legal) | 274 | 0
Originated Loans [Member] | Residential Real Estate Mortgages [Member] |  |
With no related allowance recorded [Abstract] |  |
Recorded investment balance (book) | 6,830 | 6,111
Unpaid principal balance (legal) | 8,780 | 6,906
Acquired Loans [Member] | Commercial [Member] |  |
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 0 | 1,205
Unpaid principal balance (legal) | 0 | 1,321
Total [Abstract] |  |
Related allowance | 0 | 691
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member] |  |
With an allowance recorded [Abstract] |  |
Recorded investment balance (book) | 0 | 1,205
Unpaid principal balance (legal) | 0 | 1,321
Total [Abstract] |  |
Related allowance | $ 0 | $ 691

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