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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	$ 19,528	$ 20,936	$ 20,305	$ 23,789
Interest income recognized	210	257	646	679
Originated Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	19,528	20,936	20,305	23,668
Interest income recognized	210	257	646	679
Originated Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	5,102	5,990	5,446	8,828
Interest income recognized	36	61	109	133
Originated Loans [Member] | Commercial Loans [Member] | C&I [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	433		449
Interest income recognized	0		1
Originated Loans [Member] | Commercial Loans [Member] | CRE [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	3,645		3,999
Interest income recognized	32		96
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		1,000		2,393
Interest income recognized		0		0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		2,415		3,906
Interest income recognized		48		93
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		115		147
Interest income recognized		0		1
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		1,505		1,545
Interest income recognized		11		32
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	1,024	955	998	837
Interest income recognized	4	2	12	7
Originated Loans [Member] | Consumer Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	7,907	8,313	8,140	8,415
Interest income recognized	106	114	325	335
Originated Loans [Member] | Consumer Loans [Member] | Dealer Finance [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	177		187
Interest income recognized	4		8
Originated Loans [Member] | Consumer Loans [Member] | Direct Lending [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	7,730		7,953
Interest income recognized	102		317
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		35		22
Interest income recognized		1		2
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		8,159		8,274
Interest income recognized		111		331
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		119		119
Interest income recognized		2		2
Originated Loans [Member] | Residential Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	6,519	6,633	6,719	6,425
Interest income recognized	$ 68	$ 82	212	211
Acquired Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment			0	121
Interest income recognized			0	0
Acquired Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment			0	121
Interest income recognized			0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment			0	121
Interest income recognized			$ 0	$ 0