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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	$ 20,257	$ 24,508	$ 20,668	$ 25,446
Interest income recognized	214	194	436	422
Originated Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	20,257	24,508	20,668	25,274
Interest income recognized	214	194	436	422
Originated Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	5,373	9,770	5,599	10,520
Interest income recognized	36	15	73	72
Originated Loans [Member] | Commercial Loans [Member] | C&I [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	447		457
Interest income recognized	1		1
Originated Loans [Member] | Commercial Loans [Member] | CRE [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	3,882		4,154
Interest income recognized	32		64
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		3,931		3,419
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		3,243		4,584
Interest income recognized		1		45
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		157		165
Interest income recognized		1		1
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		1,549		1,564
Interest income recognized		10		21
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	1,044	890	988	788
Interest income recognized	3	3	8	5
Originated Loans [Member] | Consumer Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	8,146	8,350	8,254	8,446
Interest income recognized	107	111	219	221
Originated Loans [Member] | Consumer Loans [Member] | Dealer Finance [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	194		188
Interest income recognized	1		4
Originated Loans [Member] | Consumer Loans [Member] | Direct Lending [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	7,952		8,066
Interest income recognized	106		215
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		25		16
Interest income recognized		1		1
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		8,205		8,310
Interest income recognized		110		220
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		120		120
Interest income recognized		0		0
Originated Loans [Member] | Residential Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	6,738	6,388	6,815	6,308
Interest income recognized	$ 71	$ 68	144	129
Acquired Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment			0	172
Interest income recognized			0	0
Acquired Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment			0	172
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	172
Interest income recognized			$ 0	$ 0