Loans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	$ 907,162		$ 907,162		$ 799,611
Individually evaluated for impairment	24,237		24,237		17,693
Loans acquired with deteriorated credit quality	3,321		3,321		3,367
Collectively evaluated for impairment	879,604		879,604		778,551
Allowance for loan losses	10,447		10,447		8,886
Allowance for loan losses related to individually evaluated for impairment	442		442		487
Allowance for loan losses related to loans acquired with deteriorated credit quality	0		0		0
Allowance for loan losses related to collectively evaluated for impairment	10,005		10,005		8,399
Net loans	896,715		896,715		790,725
Net loans, individually evaluated for impairment	23,795		23,795		17,206
Net loans, loans acquired with deteriorated credit quality	3,321		3,321		3,367
Net loans, collectively evaluated for impairment	869,599		$ 869,599		770,152
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	206,389		$ 206,389		207,423
Individually evaluated for impairment	864		864		957
Loans acquired with deteriorated credit quality	34		34		35
Collectively evaluated for impairment	205,491		205,491		206,431
Real Estate Loans [Member] | Commercial [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	273,624		273,624		252,577
Individually evaluated for impairment	13,759		13,759		5,742
Loans acquired with deteriorated credit quality	2,016		2,016		1,969
Collectively evaluated for impairment	257,849		257,849		244,866
Real Estate Loans [Member] | Agricultural [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	207,052		207,052		123,624
Individually evaluated for impairment	3,964		3,964		3,346
Loans acquired with deteriorated credit quality	733		733		738
Collectively evaluated for impairment	202,355		202,355		119,540
Real Estate Loans [Member] | Construction [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	17,074		17,074		25,441
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	17,074		17,074		25,441
Consumer [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	10,784		10,784		11,005
Individually evaluated for impairment	4		4		0
Loans acquired with deteriorated credit quality	0		0		4
Collectively evaluated for impairment	10,780		10,780		11,001
Other Commercial Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	56,222		56,222		58,639
Individually evaluated for impairment	4,228		4,228		5,994
Loans acquired with deteriorated credit quality	538		538		621
Collectively evaluated for impairment	51,456		51,456		52,024
Other Agricultural Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	34,066		34,066		23,388
Individually evaluated for impairment	1,418		1,418		1,654
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	32,648		32,648		21,734
State and Political Subdivision Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	101,951		101,951		97,514
Individually evaluated for impairment	0		0		0
Loans acquired with deteriorated credit quality	0		0		0
Collectively evaluated for impairment	101,951		101,951		97,514
First National Bank of Fredericksburg [Member]
Changes in the accretable yield for purchased credit-impaired loans [Roll Forward]
Balance at beginning of period	167	$ 464	389	$ 637
Accretion	(90)	(88)	(312)	(261)
Balance at end of period	77	$ 376	77	$ 376
Loans acquired with specific evidence of deterioration in credit quality [Abstract]
Outstanding balance	6,328		6,328		6,487
Carrying amount	$ 3,321		$ 3,321		$ 3,367