FAIR VALUE MEASUREMENTS - Unobservable Inputs Non-recurring (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Other real estate owned	$ 68	$ 122
Non-recurring \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Total	21,756	15,073
Non-recurring \| Fair value of collateral -appraised value \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Impaired loans	13,073	8,586
Other real estate owned	68	122
Non-recurring \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Impaired loans	3,467	2,207
Capitalized servicing rights	5,148	4,158
Non-recurring \| Impaired loans \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Impaired loans	$ 16,540	$ 10,793
Non-recurring \| Impaired loans \| Minimum \| Fair value of collateral -appraised value \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Loss severity	0.00%	15.70%
Appraised value	$ 150	$ 100
Non-recurring \| Impaired loans \| Minimum \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Cash flows	22	6
Non-recurring \| Impaired loans \| Maximum \| Fair value of collateral -appraised value \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Appraised value	6,915	7,545
Non-recurring \| Impaired loans \| Maximum \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Cash flows	1,090	320
Non-recurring \| Capitalized servicing rights \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Capitalized servicing rights	5,148	4,158
Non-recurring \| Other real estate owned \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Other real estate owned	68	122
Non-recurring \| Other real estate owned \| Fair value of collateral -appraised value \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Appraised value	$ 75	$ 136
Selling Costs	10.00%	10.00%
Measurement Input, Loss Severity [Member] \| Non-recurring \| Impaired loans \| Maximum \| Fair value of collateral -appraised value \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Loss severity	55.00%	45.28%
Constant Prepayment Rate \| Non-recurring \| Capitalized servicing rights \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Servicing Assets and Servicing Liabilities at Fair Value, Assumptions Used to Estimate Fair Value, Prepayment Speed	8.05%	10.97%
Discount Rate \| Non-recurring \| Impaired loans \| Minimum \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Discount rate	2.88%	2.63%
Discount Rate \| Non-recurring \| Impaired loans \| Maximum \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Discount rate	7.00%	9.50%
Discount Rate \| Non-recurring \| Capitalized servicing rights \| Discount cash flow \| Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items}
Discount rate	10.09%	10.10%

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Fair Value Inputs, Cash Flow

+ References

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Fair Value Inputs, Selling Costs

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- Definition

Represents the amount of impaired loans assets reported on the balance sheet at period end measured at fair value by the entity.

+ References

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
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- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

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- Definition

Percentage of contractually collectible principal associated with a financial asset expected not to be collected due to default by the borrower.

+ References

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- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

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