Loans, Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	$ 9,979	$ 7,359	$ 8,886	$ 7,106
Charge-offs	(56)	(173)	(240)	(272)
Recoveries	24	508	61	590
Provision	500	500	1,740	770
Balance at end of period	10,447	8,194	10,447	8,194
Real Estate Loans [Member] | Residential [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	1,104	990	1,064	905
Charge-offs	(11)	(9)	(104)	(52)
Recoveries	0	0	0	0
Provision	(13)	32	120	160
Balance at end of period	1,080	1,013	1,080	1,013
Real Estate Loans [Member] | Commercial [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	3,541	3,338	3,589	3,376
Charge-offs	0	(100)	(41)	(100)
Recoveries	5	467	11	475
Provision	36	(90)	23	(136)
Balance at end of period	3,582	3,615	3,582	3,615
Real Estate Loans [Member] | Agricultural [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	2,452	581	1,494	409
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	242	410	1,200	582
Balance at end of period	2,694	991	2,694	991
Real Estate Loans [Member] | Construction [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	45	18	47	24
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	(14)	16	(16)	10
Balance at end of period	31	34	31	34
Consumer [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	125	104	122	102
Charge-offs	(45)	(27)	(90)	(65)
Recoveries	13	16	35	84
Provision	44	16	70	(12)
Balance at end of period	137	109	137	109
Other Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	1,131	1,316	1,327	1,183
Charge-offs	0	(37)	0	(55)
Recoveries	5	25	14	31
Provision	(24)	39	(229)	184
Balance at end of period	1,112	1,343	1,112	1,343
Other Agricultural Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	431	248	312	122
Charge-offs	0	0	(5)	0
Recoveries	1	0	1	0
Provision	30	51	154	177
Balance at end of period	462	299	462	299
State and Political Subdivision Loans [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	838	764	833	593
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	36	7	41	178
Balance at end of period	874	771	874	771
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period	312	0	98	392
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	163	19	377	(373)
Balance at end of period	$ 475	$ 19	$ 475	$ 19