MORTGAGE SERVICING RIGHTS - Mortgage Loans Serviced for Others (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Schedule of Loans Serviced for Others [Line Items]
Total mortgage loans serviced for others	$ 381,064	$ 513,479
Federal Home Loan Mortgage Corporation ("Freddie Mac")
Schedule of Loans Serviced for Others [Line Items]
Total mortgage loans serviced for others	274,331	379,339
Other financial institutions
Schedule of Loans Serviced for Others [Line Items]
Total mortgage loans serviced for others	$ 106,733	$ 134,140

Principal amount of transferred financial assets in which the transferor has continuing involvement with the assets underlying the transaction. Continuing involvement includes, but is not limited to, servicing, recourse, and restrictions on transferor's interests in transferred financial assets.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=121570589&loc=d3e107314-111719

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