FAIR VALUE - FAIR VALUE ON NON-RECURRING (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Impaired Loans
Valuation allowance of impaired loans	$ 23,000	$ 541,000	$ 648,000
Other real estate owned, net:
Outstanding balance of other real estate owned	2,404,000	1,824,000	2,347,000
Valuation allowance of other real estate owned	777,000	803,000	616,000	$ 1,583,000
Loan servicing rights
Mortgage servicing rights	1,511,000	1,321,000
Balance of loan servicing rights	1,511,000	1,321,000	1,277,000	1,209,000
Valuation allowance of loan servicing rights	56,000	125,000	$ 20,000	$ 79,000
Non-recurring
Impaired Loans
Impaired loans, at fair value	183,000	3,900,000
Valuation allowance of impaired loans	$ 23,000	502,000
Number of impaired loans. | item	1
Impaired loans, additional provision for loan losses	$ 23,000	427,000
Loan loss provision expense for impaired loans		4
Decreased in allowance for specific impaired loans	(518,000)
Other real estate owned, net:
Other real estate owned	1,100,000	1,200,000
Outstanding balance of other real estate owned	1,900,000	2,000,000
Valuation allowance of other real estate owned	777,000	803,000
Write downs of other real estate owned	20,000	187,000
Loan servicing rights
Mortgage servicing rights	1,300,000	1,100,000
Balance of loan servicing rights	1,400,000	1,200,000
Valuation allowance of loan servicing rights	56,000	125,000
Write-downs of loan servicing rights	69,000	(105,000)
Non-recurring | Carrying Value
Loan servicing rights
Mortgage servicing rights	1,323,000	1,083,000
Non-recurring | Significant Unobservable Inputs (Level 3)
Loan servicing rights
Mortgage servicing rights	1,323,000	1,083,000
Non-recurring | 1-4 family residential | Carrying Value
Impaired Loans
Impaired loans, at fair value	183,000
Non-recurring | 1-4 family residential | Significant Unobservable Inputs (Level 3)
Impaired Loans
Impaired loans, at fair value	183,000
Non-recurring | Multi-family residential | Carrying Value
Impaired Loans
Impaired loans, at fair value		1,685,000
Non-recurring | Multi-family residential | Significant Unobservable Inputs (Level 3)
Impaired Loans
Impaired loans, at fair value		1,685,000
Non-recurring | Agricultural | Carrying Value
Impaired Loans
Impaired loans, at fair value		2,234,000
Non-recurring | Agricultural | Significant Unobservable Inputs (Level 3)
Impaired Loans
Impaired loans, at fair value		2,234,000
Non-recurring | Residential | Carrying Value
Other real estate owned, net:
Other real estate owned	910,000	956,000
Non-recurring | Residential | Significant Unobservable Inputs (Level 3)
Other real estate owned, net:
Other real estate owned	910,000	956,000
Non-recurring | Commercial | Carrying Value
Impaired Loans
Impaired loans, at fair value		272,000
Other real estate owned, net:
Other real estate owned	200,000
Non-recurring | Commercial | Significant Unobservable Inputs (Level 3)
Impaired Loans
Impaired loans, at fair value		$ 272,000
Other real estate owned, net:
Other real estate owned	$ 200,000