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
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