LOANS AND RELATED ALLOWANCE FOR LOAN LOSSES (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	$ 1,115,569	$ 1,081,883
Individually evaluated for impairment	19,672	23,450
Loans acquired with deteriorated credit quality	1,282	1,859
Collectively evaluated for impairment	1,094,615	1,056,574
Allowance for loan losses	13,845	12,884
Allowance for loan losses related to individually evaluated for impairment	735	676	$ 410
Allowance for loan losses related to loans acquired with deteriorated credit quality	0	0
Allowance for loan losses related to collectively evaluated for impairment	13,110	12,208	10,780
Net loans	1,101,724	1,068,999
Net loans, individually evaluated for impairment	18,937	22,774
Net loans, loans acquired with deteriorated credit quality	1,282	1,859
Net loans, collectively evaluated for impairment	1,081,505	1,044,366
Net unamortized loan fees and costs	937	918
Real estate loans serviced for Freddie Mac and Fannie Mae	148,889	142,972
Real estate loans sold to Freddie Mac and Fannie Mae without recourse	127,402	122,219
Portfolio balance under MPF	21,487	24,853
First-loss position for MPF maintained by FHLB	143
Credit enhancement for MPF by FHLB	$ 764
Number of days past for loan to be considered impaired, Minimum	90 days
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	$ 217,088	215,305
Individually evaluated for impairment	1,166	890
Loans acquired with deteriorated credit quality	23	28
Collectively evaluated for impairment	215,899	214,387
Allowance for loan losses related to individually evaluated for impairment	32	24	56
Allowance for loan losses related to collectively evaluated for impairment	1,082	1,081	993
Real Estate Loans [Member] \| Commercial [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	342,023	319,265
Individually evaluated for impairment	11,537	13,327
Loans acquired with deteriorated credit quality	1,210	1,321
Collectively evaluated for impairment	329,276	304,617
Allowance for loan losses related to individually evaluated for impairment	251	216	94
Allowance for loan losses related to collectively evaluated for impairment	4,298	3,899	3,773
Real Estate Loans [Member] \| Agricultural [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	311,464	284,520
Individually evaluated for impairment	3,782	5,592
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	307,682	278,928
Allowance for loan losses related to individually evaluated for impairment	151	84	3
Allowance for loan losses related to collectively evaluated for impairment	4,871	4,180	3,140
Real Estate Loans [Member] \| Construction [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	15,519	33,913
Individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	15,519	33,913
Allowance for loan losses related to individually evaluated for impairment	0	0	0
Allowance for loan losses related to collectively evaluated for impairment	43	58	23
Consumer [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	9,947	9,858
Individually evaluated for impairment	4	0
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	9,943	9,858
Allowance for loan losses related to individually evaluated for impairment	0	0	0
Allowance for loan losses related to collectively evaluated for impairment	112	120	124
Other Commercial Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	69,970	74,118
Individually evaluated for impairment	1,902	2,206
Loans acquired with deteriorated credit quality	49	510
Collectively evaluated for impairment	68,019	71,402
Allowance for loan losses related to individually evaluated for impairment	147	193	231
Allowance for loan losses related to collectively evaluated for impairment	1,108	1,161	1,041
Other Agricultural Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	55,112	42,186
Individually evaluated for impairment	1,281	1,435
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	53,831	40,751
Allowance for loan losses related to individually evaluated for impairment	154	159	26
Allowance for loan losses related to collectively evaluated for impairment	807	593	466
State and Political Subdivision Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables	94,446	102,718
Individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality	0	0
Collectively evaluated for impairment	94,446	102,718
Allowance for loan losses related to individually evaluated for impairment	0	0	0
Allowance for loan losses related to collectively evaluated for impairment	536	762	$ 816
First National Bank of Fredericksburg [Member]
Changes in the accretable yield for purchased credit-impaired loans [Roll Forward]
Balance at beginning of period	104	106
Accretion	(15)	(95)
Reclassification of non-accretable discount	0	93
Balance at end of period	89	104
Loans acquired with specific evidence of deterioration in credit quality [Abstract]
Outstanding balance	4,072	4,529
Carrying amount	$ 1,282	$ 1,859

Amount of credit enhancement for Mortgage Partnership Finance Program Portfolio losses by Federal Home Loan Bank.

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The balance of financing receivables that were acquired with deteriorated credit quality.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements, related to loans acquired with deteriorated credit quality.

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale. Related to Collectively evaluated for impairment.

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The number of days past due before a loan is classified as impaired.

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Real estate loans serviced for Freddie Mac and Fannie Mae, which are not included in the consolidated balance sheet.

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Real estate loans sold to Freddie Mac and Fannie Mae without recourse which are not included in the consolidated balance sheet.

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Amount of the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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Amount of accretion recognized for the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities, with evidence of deterioration of credit quality.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of increase of reclassification from nonaccretable difference to the excess of a loan's cash flows expected to be collected over the investor's initial investment in acquired loans not accounted for as debt securities with evidence of deterioration of credit quality.

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The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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