MORTGAGE SERVICING RIGHTS - Balance of loans serviced for others and fair value of mortgage servicing rights (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2019	Dec. 31, 2018
Residential mortgage loans serviced for others		$ 111,378
Balance of loans serviced for others and fair value of mortgage servicing rights
Residential mortgage loans serviced for others	$ 106,365
Fair value of mortgage servicing rights	$ 765	$ 951

The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant