LOANS - Fair Value and Unpaid Principal of Residential Mortgage Loan Portfolio (Details) - Residential mortgage loans - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Mortgage Loans on Real Estate [Line Items]
Fair value	$ 1,983,015	$ 1,438,322
Unpaid principal balance	$ 1,976,077	$ 1,419,807

This is the result of the principal amount outstanding of total loans managed or securitized less securitized loans and loans that are in the process of being securitized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82924980&loc=d3e107314-111719

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