FAIR VALUE - Quantitative Information about Level 3 Value Measurements - (Details) - Non-recurring basis - Significant Unobservable Inputs (Level 3) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Impaired Loans
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 6,889	$ 2,537
Impaired Loans | Commercial and industrial | Sales comparison approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 855	$ 260
Impaired Loans | Commercial and industrial | Sales comparison approach | Minimum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	19.00%	10.00%
Impaired Loans | Commercial and industrial | Sales comparison approach | Maximum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	30.00%	30.00%
Impaired Loans | Commercial and industrial | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	24.00%	18.00%
Impaired Loans | Agricultural | Sales comparison approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 779	$ 972
Impaired Loans | Agricultural | Sales comparison approach | Minimum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	16.00%
Impaired Loans | Agricultural | Sales comparison approach | Maximum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	25.00%
Impaired Loans | Agricultural | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	24.00%	10.00%
Impaired Loans | Hotel | Sales comparison approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 2,715
Impaired Loans | Hotel | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	40.00%
Impaired Loans | Farm | Sales comparison approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 794	$ 745
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)		10.00%
Impaired Loans | Farm | Sales comparison approach | Minimum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	16.00%
Impaired Loans | Farm | Sales comparison approach | Maximum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	(25.00%)
Impaired Loans | Farm | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	22.00%	10.00%
Impaired Loans | Other real estate | Sales comparison approach
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 1,746	$ 560
Impaired Loans | Other real estate | Sales comparison approach | Minimum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	19.00%	16.00%
Impaired Loans | Other real estate | Sales comparison approach | Maximum
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	40.00%	31.00%
Impaired Loans | Other real estate | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)	27.00%
Impaired Loans | Other | Sales comparison approach | Average
Unobservable Inputs
Adjustment for differences between comparable sales, type of property, current status of property (as a percent)		27.00%
Mortgage servicing rights | Cash flow analysis
Quantitative information about level 3 fair value measurements for financial instruments measured at fair value
Fair Value	$ 928	$ 1,083
Unobservable Inputs
Discount rate (as a percent)	10.00%	10.00%