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, 2018	Dec. 31, 2017	Dec. 31, 2016
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	$ 20,429	$ 23,238	$ 30,132
Interest income recognized accrual	901	924	970
Originated Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	20,429	23,145	28,927
Interest income recognized accrual	901	924	970
Originated Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	5,549	8,183	14,498
Interest income recognized accrual	155	171	221
Originated Loans [Member] | Commercial Loans [Member] | C&I [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	453	0	0
Interest income recognized accrual	1	0	0
Originated Loans [Member] | Commercial Loans [Member] | CRE [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	4,078	0	0
Interest income recognized accrual	128	0	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	1,841	6,217
Interest income recognized accrual	0	0	0
Originated Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	3,534	5,828
Interest income recognized accrual	0	115	167
Originated Loans [Member] | Commercial Loans [Member] | Agricultural [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	224	715
Interest income recognized accrual	0	1	1
Originated Loans [Member] | Commercial Loans [Member] | Agricultural Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	1,709	908
Interest income recognized accrual	0	43	44
Originated Loans [Member] | Commercial Loans [Member] | Business Banking [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	1,018	875	830
Interest income recognized accrual	26	12	9
Originated Loans [Member] | Consumer Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	8,101	8,439	8,286
Interest income recognized accrual	441	457	480
Originated Loans [Member] | Consumer Loans [Member] | Dealer Finance [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	179	0	0
Interest income recognized accrual	10	0	0
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	7,922
Interest income recognized accrual	431
Originated Loans [Member] | Consumer Loans [Member] | Indirect [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	35	8
Interest income recognized accrual	0	3	0
Originated Loans [Member] | Consumer Loans [Member] | Home Equity [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	8,226	8,278
Interest income recognized accrual	0	446	480
Originated Loans [Member] | Consumer Loans [Member] | Direct [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment		178	0
Interest income recognized accrual		8	0
Originated Loans [Member] | Residential Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	6,779	6,523	6,143
Interest income recognized accrual	305	296	269
Acquired Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	93	1,205
Interest income recognized accrual	0	0	0
Acquired Loans [Member] | Commercial Loans [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	93	1,205
Interest income recognized accrual	0	0	0
Acquired Loans [Member] | Commercial Loans [Member] | Commercial Real Estate [Member]
Average Recorded Investment and Interest Income Recognized [Abstract]
Average recorded investment	0	93	1,205
Interest income recognized accrual	$ 0	$ 0	$ 0