FAIR VALUE (Quantitative Information about Level 3 fair value measurements) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	$ 7,030	$ 7,258
Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets	800	725
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	67,224
Derivative assets	0	0
Level 3 | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets	800	725
Level 3 | Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale		67,224
Commercial servicing rights	6,459	7,143
Level 3 | Modified appraised value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	5,391	6,153
Level 3 | Modified appraised value | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	9,998	12,932
Level 3 | Modified appraised value | Commercial Real Estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	717	405
Level 3 | Modified appraised value | Agricultural and agricultural real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	8,932	11,070
Level 3 | Modified appraised value | Residential real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,207	478
Level 3 | Modified appraised value | Consumer
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	633	624
Level 3 | Modified appraised value | Recurring Basis | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	7,030	7,258
Level 3 | Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets	800	725
Level 3 | Interest rate lock commitments | Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets	$ 800	$ 725
Closing ratio | Level 3 | Weighted Average | Interest rate lock commitments | PrimeWest Mortgage Corporation
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.89
Closing ratio | Level 3 | Discounted cash flows | Weighted Average | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.89	0.91
Closing ratio | Level 3 | Discounted cash flows | Minimum | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input	0.00	0.00
Closing ratio | Level 3 | 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 | Level 3 | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Appraisal discount | Level 3 | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	10.00%	10.00%
Appraisal discount | Level 3 | Modified appraised value | Premises, furniture and equipment held for sale | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Appraisal discount | Level 3 | Modified appraised value | Premises, furniture and equipment held for sale | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	10.00%	10.00%
Agricultural and agricultural real estate | Appraisal discount | Level 3 | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Agricultural and agricultural real estate | Appraisal discount | Level 3 | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	15.00%	24.00%
Residential real estate | Appraisal discount | Level 3 | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Residential real estate | Appraisal discount | Level 3 | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	12.00%	24.00%
Consumer | Valuation discount | Level 3 | Modified appraised value | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Consumer | Valuation discount | Level 3 | Modified appraised value | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	9.00%	14.00%
Commercial | Appraisal discount | Level 3 | Modified appraised value | Commercial | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Commercial | Appraisal discount | Level 3 | Modified appraised value | Commercial | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	18.00%	8.00%
Commercial | Appraisal discount | Level 3 | Modified appraised value | Commercial Real Estate | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	0.00%	0.00%
Commercial | Appraisal discount | Level 3 | Modified appraised value | Commercial Real Estate | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Servicing assets, discount rate	9.00%	19.00%