NATURE OF BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) branch lease segment	Dec. 31, 2019 USD ($) segment reporting_unit	Mar. 31, 2019 USD ($)	Jan. 01, 2019 USD ($) lease
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other investments	$ 14,999	$ 15,005
Interest income recognized debt past due (less than days)	90 days
Loans charged off past due more than days	180 days
Closed end loan charged off past due more than days	120 days
Number of operating segments | segment	1	1
Number of reporting units | reporting_unit		1
Operating lease right-of-use assets	$ 2,577	$ 2,787		$ 5,000
Operating lease liabilities	$ 2,697	2,845		$ 5,000
Corporate Offices
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties subject to operating leases (in leases) | lease	1			1
Other Production
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties subject to operating leases (in leases) | lease	1			1
Equipment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties subject to operating leases (in leases) | lease	4			4
Bank Branch
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of properties subject to operating leases (in leases) | lease	6			9
Accounting Standards Update 2016-01
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cumulative effect of new accounting principle				$ 0
Retained Earnings
Accounts, Notes, Loans and Financing Receivable [Line Items]
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect			$ (137)
Retained Earnings | Accounting Standards Update 2016-01
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cumulative effect of new accounting principle				45
Accumulated Other Comprehensive Income (Loss)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Tax Cuts and Jobs Act, Reclassification from AOCI to Retained Earnings, Tax Effect			$ 137
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2016-01
Accounts, Notes, Loans and Financing Receivable [Line Items]
Cumulative effect of new accounting principle				$ (45)
FHLB
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other investments	$ 8,158	8,196
Federal Reserve Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other investments	5,166	5,162
Bankers Bank Stock
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other investments	$ 1,675	$ 1,647
Commercial Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income discontinued over delinquent days	90 days
Closed End Consumer Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income discontinued over delinquent days	120 days
Real Estate and Open Ended Consumer Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income discontinued over delinquent days	180 days
Wisconsin and Minnesota
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Offices | branch	28