FAIR VALUE (Quantitative Information about Level 3 fair value measurements) (Details) - Significant Unobservable Inputs (Level 3) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative instruments	$ 0	$ 0
Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative instruments	1,204	1,827
Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing rights	5,801	5,189
Modified appraised value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	4,744	6,624
Modified appraised value | Agricultural and agricultural real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	9,145	12,451
Modified appraised value | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	2,699	6,499
Interest rate lock commitments | Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative instruments	$ 1,204	$ 1,827
Closing ratio | Discounted cash flows | Weighted Average | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.88	0.86
Closing ratio | Discounted cash flows | Minimum | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0	0
Closing ratio | Discounted cash flows | Maximum | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.99	0.99
Appraisal discount | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Appraisal discount | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	10.00%	10.00%
Appraisal discount | Modified appraised value | Premises, furniture and equipment held for sale | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Appraisal discount | Modified appraised value | Premises, furniture and equipment held for sale | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	10.00%	10.00%
Commercial and industrial | Modified appraised value | Commercial and industrial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 10,270	$ 11,256
Commercial and industrial | Modified appraised value | Owner occupied commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	3,552	5,874
Commercial and industrial | Modified appraised value | Non-owner occupied commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 15,212	$ 4,907
Commercial and industrial | Appraisal discount | Modified appraised value | Commercial and industrial | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Commercial and industrial | Appraisal discount | Modified appraised value | Commercial and industrial | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	15.00%	8.00%
Commercial and industrial | Appraisal discount | Modified appraised value | Owner occupied commercial real estate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Commercial and industrial | Appraisal discount | Modified appraised value | Owner occupied commercial real estate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	11.00%	12.00%
Commercial and industrial | Appraisal discount | Modified appraised value | Non-owner occupied commercial real estate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Commercial and industrial | Appraisal discount | Modified appraised value | Non-owner occupied commercial real estate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	11.00%	10.00%
Agricultural and agricultural real estate | Appraisal discount | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	0.00%	0.00%
Agricultural and agricultural real estate | Appraisal discount | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate (as a percent)	10.00%	10.00%