Loans, Primary Segments Portfolio and Accretable Yield for PCI Loans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	$ 1,099,622		$ 1,099,622		$ 1,081,883
Individually evaluated for impairment	21,521		21,521		23,450
Loans acquired with deteriorated credit quality	1,574		1,574		1,859
Collectively evaluated for impairment	1,076,527		1,076,527		1,056,574
Allowance for loan losses	13,304		13,304		12,884
Individually evaluated for impairment	803		803		676
Allowance for loan losses related to loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	12,501		12,501		12,208
Net loans	1,086,318		1,086,318		1,068,999
Net loans, individually evaluated for impairment	20,718		20,718		22,774
Net loans, loans acquired with deteriorated credit quality	1,574		1,574		1,859
Net loans, collectively evaluated for impairment	1,064,026		$ 1,064,026		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	213,014		$ 213,014		215,305
Individually evaluated for impairment	1,186		1,186		890
Loans acquired with deteriorated credit quality	26		26		28
Collectively evaluated for impairment	211,802		211,802		214,387
Individually evaluated for impairment	23		23		24
Collectively evaluated for impairment	1,043		1,043		1,081
Real Estate Loans [Member] | Commercial [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	347,430		347,430		319,265
Individually evaluated for impairment	11,969		11,969		13,327
Loans acquired with deteriorated credit quality	1,228		1,228		1,321
Collectively evaluated for impairment	334,233		334,233		304,617
Individually evaluated for impairment	333		333		216
Collectively evaluated for impairment	4,067		4,067		3,899
Real Estate Loans [Member] | Agricultural [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	294,332		294,332		284,520
Individually evaluated for impairment	4,816		4,816		5,592
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	289,516		289,516		278,928
Individually evaluated for impairment	146		146		84
Collectively evaluated for impairment	4,386		4,386		4,180
Real Estate Loans [Member] | Construction [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	20,950		20,950		33,913
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	20,950		20,950		33,913
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	36		36		58
Consumer [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	9,854		9,854		9,858
Individually evaluated for impairment	5		5		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	9,849		9,849		9,858
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	118		118		120
Other Commercial Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	76,179		76,179		74,118
Individually evaluated for impairment	2,134		2,134		2,206
Loans acquired with deteriorated credit quality	320		320		510
Collectively evaluated for impairment	73,725		73,725		71,402
Individually evaluated for impairment	143		143		193
Collectively evaluated for impairment	1,185		1,185		1,161
Other Agricultural Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	41,689		41,689		42,186
Individually evaluated for impairment	1,411		1,411		1,435
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	40,278		40,278		40,751
Individually evaluated for impairment	158		158		159
Collectively evaluated for impairment	583		583		593
State and Political Subdivision Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	96,174		96,174		102,718
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	96,174		96,174		102,718
Individually evaluated for impairment	0		0		0
Collectively evaluated for impairment	539		539		762
First National Bank of Fredericksburg [Member]
Changes in the accretable yield for purchased credit-impaired loans [Roll Forward]
Balance at beginning of period	102	$ 82	104	$ 106
Accretion	(2)	(23)	(4)	(47)
Balance at end of period	100	$ 59	100	$ 59
Loans acquired with specific evidence of deterioration in credit quality [Abstract]
Outstanding balance	4,332		4,332		4,529
Carrying amount	$ 1,574		$ 1,574		$ 1,859