LOANS AND RELATED ALLOWANCE FOR LOAN LOSSES (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 11, 2015	Dec. 31, 2014
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												$ 799,611	$ 695,031
Individually evaluated for impairment												17,693	12,284
Loans acquired with deteriorated credit quality												3,367	3,818
Collectively evaluated for impairment												778,551	678,929
Less: Allowance for loan losses												8,886	7,106
Allowance for loan losses related to individually evaluated for impairment												487	355
Allowance for loan losses related to loans acquired with deteriorated credit quality												0	0
Allowance for loan losses related to collectively evaluated for impairment												8,399	6,751
Net loans												790,725	687,925
Net loans, individually evaluated for impairment												17,206	11,929
Net loans, loans acquired with deteriorated credit quality												3,367	3,818
Net loans, collectively evaluated for impairment												770,152	672,178
Real estate loans serviced for Freddie Mac and Fannie Mae												135,404	133,210
Real estate loans sold to Freddie Mac and Fannie Mae without recourse									$ 102,444	$ 92,773
Portfolio balance under MPF												32,960	40,437
First-loss position for MPF maintained by FHLB												120
Credit enhancement for MPF by FHLB									$ 985
Net unamortized loan fees and costs												732	1,170
Number of days past for loan to be considered impaired, Minimum									90 days
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				$ 7,106				$ 6,815	$ 7,106	6,815	$ 7,098
Charge-offs									(340)	(238)	(910)
Recoveries									600	49	42
Provision	$ 750	$ 500	$ 135	135	$ 120	$ 120	$ 120	120	1,520	480	585
Balance at end of period	8,886				7,106				$ 8,886	7,106	6,815
Individually evaluated for impairment												487	355		$ 98
Collectively evaluated for impairment												8,399	6,751		6,717
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
Commercial [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												252,577	237,542
Individually evaluated for impairment												5,742	6,068
Loans acquired with deteriorated credit quality												1,969	2,170
Collectively evaluated for impairment												244,866	229,304
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				3,376				3,419	$ 3,376	3,419	3,983
Charge-offs									(100)	(84)	(516)
Recoveries									479	14	15
Provision									(166)	27	(63)
Balance at end of period	3,589				3,376				3,589	3,376	3,419
Individually evaluated for impairment												45	62		72
Collectively evaluated for impairment												3,544	3,314		3,347
Agricultural [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												123,624	57,822
Individually evaluated for impairment												3,346	167
Loans acquired with deteriorated credit quality												738	738
Collectively evaluated for impairment												119,540	56,917
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				409				451	409	451	575
Charge-offs									0
Recoveries									0
Provision									1,085	(42)	(124)
Balance at end of period	1,494				409				1,494	409	451
Individually evaluated for impairment												54	0
Collectively evaluated for impairment												1,440	409		451
Residential Real Estate Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												207,423	203,407
Individually evaluated for impairment												957	304
Loans acquired with deteriorated credit quality												35	35
Collectively evaluated for impairment												206,431	203,068
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				905				878	905	878	946
Charge-offs									(85)	(66)	(97)
Recoveries									0	0	0
Provision									244	93	29
Balance at end of period	1,064				905				1,064	905	878
Individually evaluated for impairment												32	37		25
Collectively evaluated for impairment												1,032	868		853
Construction [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												25,441	15,011
Individually evaluated for impairment												0	0
Loans acquired with deteriorated credit quality												0	0
Collectively evaluated for impairment												25,441	15,011
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				24				26	24	26	50
Charge-offs									0	0	0
Recoveries									0	0	0
Provision									23	(2)	(24)
Balance at end of period	47				24				47	24	26
Individually evaluated for impairment												0	0		0
Collectively evaluated for impairment												47	24		26
Consumer [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												11,005	11,543
Individually evaluated for impairment												0	0
Loans acquired with deteriorated credit quality												4	9
Collectively evaluated for impairment												11,001	11,534
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				102				84	102	84	105
Charge-offs									(100)	(47)	(47)
Recoveries									88	33	27
Provision									32	32	(1)
Balance at end of period	122				102				122	102	84
Individually evaluated for impairment												0	0		0
Collectively evaluated for impairment												122	102		84
Other Commercial Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												58,639	57,549
Individually evaluated for impairment												5,994	5,640
Loans acquired with deteriorated credit quality												621	866
Collectively evaluated for impairment												52,024	51,043
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				1,183				1,007	1,183	1,007	686
Charge-offs									(55)	(41)	(250)
Recoveries									33	2	0
Provision									166	215	571
Balance at end of period	1,327				1,183				1,327	1,183	1,007
Individually evaluated for impairment												326	256		1
Collectively evaluated for impairment												1,001	927		1,006
Other Agricultural Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												23,388	13,657
Individually evaluated for impairment												1,654	105
Loans acquired with deteriorated credit quality												0
Collectively evaluated for impairment												21,734	13,552
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				122				217	122	217	256
Charge-offs									0
Recoveries									0
Provision									190	(95)	(39)
Balance at end of period	312				122				312	122	217
Individually evaluated for impairment												30
Collectively evaluated for impairment												282	122		217
State and Political Subdivision Loans [Member]
Segments of loan portfolio and allowance for loan losses [Abstract]
Total financing receivables												97,514	98,500
Individually evaluated for impairment												0	0
Loans acquired with deteriorated credit quality												0	0
Collectively evaluated for impairment												97,514	98,500
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				593				545	593	545	330
Charge-offs									0	0	0
Recoveries									0	0	0
Provision									240	48	215
Balance at end of period	833				593				833	593	545
Individually evaluated for impairment												0	0		0
Collectively evaluated for impairment												833	593		545
Unallocated [Member]
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Balance at beginning of period				392				188	392	188	167
Charge-offs									0	0	0
Recoveries									0	0	0
Provision									(294)	204	21
Balance at end of period	98				392				98	392	188
Individually evaluated for impairment												0	0		0
Collectively evaluated for impairment												98	392		188
First National Bank of Fredericksburg [Member]
Components of the purchase accounting adjustments related to the purchased impaired loans in FNB Acquisition [Abstract]
Estimated fair value														$ 3,809
Contractually required principal and interest at acquisition														9,913
Expected cash flows														4,474
Non-accretable discount														5,439
Accretable discount	389			637	637			665	637	665	665	389	637	665	$ 665
Changes in the accretable yield for purchased credit-impaired loans [Roll Forward]
Balance at beginning of period				$ 637				$ 665	637	665
Accretion									(349)	(28)
Reclassification of non-accretable discount									101	0
Balance at end of period	$ 389				$ 637				$ 389	$ 637	$ 665
Loans acquired with specific evidence of deterioration in credit quality [Abstract]
Outstanding balance												6,487	6,950	$ 6,969
Carrying amount												$ 3,367	$ 3,818