FAIR VALUE - QUANTITATIVE INFORMATION (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Fair Value Measurements
Mortgage servicing rights	$ 1,511	$ 1,321
Non-recurring
Fair Value Measurements
Impaired loans, at fair value	183	3,900
Other real estate owned	1,100	1,200
Mortgage servicing rights	1,300	1,100
Non-recurring \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Mortgage servicing rights	1,323	1,083
Non-recurring \| Discounted cash flow \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Mortgage servicing rights	1,323	1,083
Non-recurring \| 1-4 family residential \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value	183
Non-recurring \| 1-4 family residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value	183	1,685
Non-recurring \| Multi-family residential \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value		1,685
Non-recurring \| Agricultural \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value		2,234
Non-recurring \| Agricultural \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value		2,234
Non-recurring \| Residential \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Other real estate owned	910	956
Non-recurring \| Residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Other real estate owned	910	956
Non-recurring \| Commercial \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value		272
Other real estate owned	200
Non-recurring \| Commercial \| Income approach \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Impaired loans, at fair value	$ 200	$ 272
Non-recurring \| Minimum \| Discounted cash flow \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Constant prepayment rates (as a percent)	7.00%	8.00%
Non-recurring \| Minimum \| 1-4 family residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	3.00%	0.00%
Non-recurring \| Minimum \| Agricultural \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)		2.00%
Non-recurring \| Minimum \| Residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	0.00%	1.00%
Non-recurring \| Minimum \| Commercial \| Income approach
Fair Value Measurements
Capitalization rate (as a percent)		10.00%
Non-recurring \| Minimum \| Commercial \| Income approach \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Capitalization rate (as a percent)	10.00%
Non-recurring \| Maximum \| Discounted cash flow \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Constant prepayment rates (as a percent)	25.00%	45.00%
Non-recurring \| Maximum \| 1-4 family residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	27.00%	21.00%
Non-recurring \| Maximum \| Agricultural \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)		75.00%
Non-recurring \| Maximum \| Residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	16.00%	16.00%
Non-recurring \| Maximum \| Commercial \| Income approach \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Capitalization rate (as a percent)	10.00%	10.00%
Non-recurring \| Weighted average \| Discounted cash flow \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Constant prepayment rates (as a percent)	10.00%	13.00%
Non-recurring \| Weighted average \| 1-4 family residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	15.00%	10.00%
Non-recurring \| Weighted average \| Agricultural \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)		9.00%
Non-recurring \| Weighted average \| Residential \| Sales comparison \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Adjustment for differences between the comparable sales (as a percent)	6.00%	9.00%
Non-recurring \| Weighted average \| Commercial \| Income approach \| Significant Unobservable Inputs (Level 3)
Fair Value Measurements
Capitalization rate (as a percent)	10.00%	10.00%

Fair value as of the balance sheet date of impaired financing receivables.

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- Definition

Represents the fair value of real estate acquired through foreclosure.

+ References

No definition available.

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- Definition

Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Percentage of adjustment to the observed price for a similar asset or liability when an identical transaction does not exist, used as an input to measure fair value.

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Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

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