Loans, Primary Segments Portfolio and Accretable Yield for PCI Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	$ 1,115,034		$ 1,115,034		$ 1,081,883
Individually evaluated for impairment	21,352		21,352		23,450
Loans acquired with deteriorated credit quality	1,328		1,328		1,859
Collectively evaluated for impairment	1,092,354		1,092,354		1,056,574
Allowance for loan losses	13,679		13,679		12,884
Individually evaluated for impairment	810		810		676
Allowance for loan losses related to loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	12,869		12,869		12,208
Net loans	1,101,355		1,101,355		1,068,999
Net loans, individually evaluated for impairment	20,542		20,542		22,774
Net loans, loans acquired with deteriorated credit quality	1,328		1,328		1,859
Net loans, collectively evaluated for impairment	1,079,485		$ 1,079,485		1,044,366
Minimum [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Number of days past for loan to be considered impaired, Minimum			90 days
First Mortgage [Member] | Minimum [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Period of mortgage on real estate			15 years
First Mortgage [Member] | Maximum [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Period of mortgage on real estate			30 years
Second Mortgage [Member] | Maximum [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Period of mortgage on real estate			15 years
Real Estate Loans [Member] | Residential [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	215,717		$ 215,717		215,305
Individually evaluated for impairment	1,195		1,195		890
Loans acquired with deteriorated credit quality	24		24		28
Collectively evaluated for impairment	214,498		214,498		214,387
Individually evaluated for impairment	22		22		24
Collectively evaluated for impairment	1,069		1,069		1,081
Real Estate Loans [Member] | Commercial [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	349,269		349,269		319,265
Individually evaluated for impairment	11,921		11,921		13,327
Loans acquired with deteriorated credit quality	1,213		1,213		1,321
Collectively evaluated for impairment	336,135		336,135		304,617
Individually evaluated for impairment	342		342		216
Collectively evaluated for impairment	4,299		4,299		3,899
Real Estate Loans [Member] | Agricultural [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	305,948		305,948		284,520
Individually evaluated for impairment	4,781		4,781		5,592
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	301,167		301,167		278,928
Individually evaluated for impairment	145		145		84
Collectively evaluated for impairment	4,567		4,567		4,180
Real Estate Loans [Member] | Construction [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	11,448		11,448		33,913
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	11,448		11,448		33,913
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	19		19		58
Consumer [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	9,709		9,709		9,858
Individually evaluated for impairment	6		6		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	9,703		9,703		9,858
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	119		119		120
Other Commercial Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	76,785		76,785		74,118
Individually evaluated for impairment	2,042		2,042		2,206
Loans acquired with deteriorated credit quality	91		91		510
Collectively evaluated for impairment	74,652		74,652		71,402
Individually evaluated for impairment	144		144		193
Collectively evaluated for impairment	1,205		1,205		1,161
Other Agricultural Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	50,334		50,334		42,186
Individually evaluated for impairment	1,407		1,407		1,435
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	48,927		48,927		40,751
Individually evaluated for impairment	157		157		159
Collectively evaluated for impairment	712		712		593
State and Political Subdivision Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	95,824		95,824		102,718
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	95,824		95,824		102,718
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	536		536		762
First National Bank of Fredericksburg [Member]
Changes in the accretable yield for purchased credit-impaired loans [Roll Forward]
Balance at beginning of period	100	$ 59	104	$ 106
Accretion	(10)	(24)	(14)	(71)
Reclassification of non-accretable discount	0	93	0	93
Balance at end of period	90	$ 128	90	$ 128
Loans acquired with specific evidence of deterioration in credit quality [Abstract]
Outstanding balance	4,076		4,076		4,529
Carrying amount	$ 1,328		$ 1,328		$ 1,859