FAIR VALUE (Quantitative Information about Level 3 fair value measurements) (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	$ 3,701	$ 7,258
Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	34,575	119,801
Collateral dependent impaired loans	24,880	25,509
Fair Value, Measurements, Nonrecurring | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	3,701	7,258
Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	1,072	725
Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	0
Interest rate lock commitments	0	0
Level 1 | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	0	0
Level 1 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	0
Collateral dependent impaired loans	0	0
Level 1 | Fair Value, Measurements, Nonrecurring | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	0	0
Level 1 | Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	0	0
Level 2
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	34,575	52,577
Interest rate lock commitments	14,413	6,539
Level 2 | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	0	0
Level 2 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	34,575	52,577
Collateral dependent impaired loans	0	0
Level 2 | Fair Value, Measurements, Nonrecurring | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	0	0
Level 2 | Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	0	0
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	67,224
Interest rate lock commitments	0	0
Level 3 | Interest rate lock commitments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	1,072	725
Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	0	67,224
Collateral dependent impaired loans	24,880	25,509
Level 3 | Fair Value, Measurements, Nonrecurring | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	3,701	7,258
Level 3 | Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale		67,224
Mortgage servicing rights	5,801	7,143
Level 3 | Modified appraised value
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Other real estate owned	6,646	6,153
Level 3 | Modified appraised value | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	13,337	12,932
Level 3 | Modified appraised value | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	808	405
Level 3 | Modified appraised value | Agricultural and agricultural real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	9,032	11,070
Level 3 | Modified appraised value | Residential real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	1,076	478
Level 3 | Modified appraised value | Consumer
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	627	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	3,701	7,258
Level 3 | Interest rate lock commitments | Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	1,072	725
Level 3 | Interest rate lock commitments | Discounted cash flows
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Interest rate lock commitments	$ 1,072	$ 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	0.90
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	0.90	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%
Commercial | Fair Value, Measurements, Nonrecurring | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 13,337	$ 12,932
Commercial | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	808	405
Commercial | Level 1 | Fair Value, Measurements, Nonrecurring | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Commercial | Level 1 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Commercial | Level 2 | Fair Value, Measurements, Nonrecurring | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Commercial | Level 2 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Commercial | Level 3 | Fair Value, Measurements, Nonrecurring | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	13,337	12,932
Commercial | Level 3 | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 808	$ 405
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	20.00%	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	20.00%	19.00%
Agricultural and agricultural real estate | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 9,032	$ 11,070
Agricultural and agricultural real estate | Level 1 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Agricultural and agricultural real estate | Level 2 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Agricultural and agricultural real estate | Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 9,032	$ 11,070
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 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 1,076	$ 478
Residential real estate | Level 1 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Residential real estate | Level 2 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Residential real estate | Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 1,076	$ 478
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	11.00%	24.00%
Consumer | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 627	$ 624
Consumer | Level 1 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Consumer | Level 2 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Consumer | Level 3 | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 627	$ 624
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	12.00%	14.00%
Changes Measurement | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Loans held for sale	$ (1,386)	$ (1,870)
Collateral dependent impaired loans	3,523	1,307
Changes Measurement | Fair Value, Measurements, Nonrecurring | Premises, furniture and equipment held for sale
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Premises, furniture and equipment held for sale	954	59
Changes Measurement | Commercial | Fair Value, Measurements, Nonrecurring | Commercial
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	3,070	660
Changes Measurement | Commercial | Fair Value, Measurements, Nonrecurring | Commercial real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	72	72
Changes Measurement | Agricultural and agricultural real estate | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	379	575
Changes Measurement | Residential real estate | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	0	0
Changes Measurement | Consumer | Fair Value, Measurements, Nonrecurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Collateral dependent impaired loans	$ 2	$ 0