DERIVATIVES AND HEDGING - Summary of Freestanding Derivative Instruments on Income (Details) - Not Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Investment income
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses from freestanding derivative instruments	$ (6,506)	$ 10,056	$ (4,777)	$ (2,317)
General and administrative expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains and losses from freestanding derivative instruments	$ (2,548)	$ 1,769	$ 13	$ (1,303)

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration