FAIR VALUE MEASUREMENTS - Unobservable Inputs Non-recurring (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Quantitative information about the significant unobservable inputs within Level 3
Other real estate owned	$ 129	$ 122
Non-recurring | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Total	21,759	15,073
Non-recurring | Fair value of collateral -appraised value | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Impaired loans	13,696	8,586
Other real estate owned	129	122
Non-recurring | Discount cash flow | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Impaired loans	2,956	2,207
Capitalized servicing rights	4,978	4,158
Non-recurring | Impaired loans | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Impaired loans	$ 16,652	$ 10,793
Non-recurring | Impaired loans | Minimum | Fair value of collateral -appraised value | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Loss severity	0.00%	15.70%
Appraised value	$ 65	$ 100
Non-recurring | Impaired loans | Minimum | Discount cash flow | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Discount rate	2.88%	2.63%
Cash flows	$ 37	$ 6
Non-recurring | Impaired loans | Maximum | Fair value of collateral -appraised value | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Loss severity	55.00%	45.28%
Appraised value	$ 6,915	$ 7,545
Non-recurring | Impaired loans | Maximum | Discount cash flow | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Discount rate	9.50%	9.50%
Cash flows	$ 1,162	$ 320
Non-recurring | Capitalized servicing rights | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Capitalized servicing rights	$ 4,978	$ 4,158
Non-recurring | Capitalized servicing rights | Discount cash flow | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Discount rate	10.09%	10.10%
Constant prepayment rate (CPR)	8.85%	10.97%
Non-recurring | Other real estate owned | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Other real estate owned	$ 129	$ 122
Non-recurring | Other real estate owned | Fair value of collateral -appraised value | Level 3
Quantitative information about the significant unobservable inputs within Level 3
Appraised value	$ 142	$ 136
Selling Costs	10.00%	10.00%