LOANS - Corporate Debt Held for Investment (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Principal payments	$ (431,867)
Sales	(1,582,198)
Corporate Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	2,144,850	$ 1,887,182
Beginning balance	2,152,213
Originations & advances	663,396	888,036
Principal payments	(273,556)	(368,927)
Amortization & accretion of (premium) discounts	6,772	8,896
Loan restructuring	(16,732)
Sales	(295,640)	(262,974)
Syndications	5,600
Net (increase) decrease in allowance		(7,363)
Current period allowance	(31,667)
Write offs	11,894
Ending allowance	(56,789)
Ending balance	2,185,264	2,144,850
Corporate Loans \| First lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	1,396,140	1,346,356
Beginning balance	1,403,503
Originations & advances	484,393	542,463
Principal payments	(247,658)	(228,302)
Amortization & accretion of (premium) discounts	4,898	5,960
Loan restructuring	(19,550)
Sales	(248,258)	(262,974)
Syndications	5,600
Net (increase) decrease in allowance		(7,363)
Current period allowance	(19,549)
Write offs	11,894
Ending allowance	(25,805)
Ending balance	1,357,123	1,396,140
Corporate Loans \| Second lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	748,710	540,826
Beginning balance	748,710
Originations & advances	179,003	345,573
Principal payments	(25,898)	(140,625)
Amortization & accretion of (premium) discounts	1,874	2,936
Loan restructuring	2,818
Sales	(47,382)	0
Syndications	0
Net (increase) decrease in allowance		0
Current period allowance	(12,118)
Write offs	0
Ending allowance	(30,984)
Ending balance	828,141	748,710
Impact of adopting CECL \| Corporate Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	(29,653)
Ending allowance		(29,653)
Impact of adopting CECL \| Corporate Loans \| First lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	(10,787)
Ending allowance		(10,787)
Impact of adopting CECL \| Corporate Loans \| Second lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	(18,866)
Ending allowance		(18,866)
CECL provision, adjusted balance \| Corporate Loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	(7,363)
Ending allowance		(7,363)
CECL provision, adjusted balance \| Corporate Loans \| First lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	(7,363)
Ending allowance		(7,363)
CECL provision, adjusted balance \| Corporate Loans \| Second lien loans
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning allowance	$ 0
Ending allowance		$ 0

Mortgage Loans on Real Estate, Restructuring

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- Definition

SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Excluding Loan Loss Allowance

+ References

No definition available.

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- Definition

SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Syndications

+ References

No definition available.

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- Definition

Amount of decrease in investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from collection of principal.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 12
-Footnote 6
-Subsection 29

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of increase (decrease) of allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

The net increase(decrease) in interest income during the period representing the allocation of deferred loan origination fees less deferred loan origination costs using the effective interest method over the term of the debt arrangement to which they pertain taking into account the effect of prepayments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 35
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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- Definition

Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
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-Paragraph 13
-Subparagraph (f)
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- Definition

Amount of writeoff of investment in debt security, measured at amortized cost (held-to-maturity), charged against allowance for credit loss.

+ References

+ Details

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- Definition

Amount of expense (reversal of expense) for expected credit loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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- Definition

Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of decrease in investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, from sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 6))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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- Definition

Amount of addition to investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Footnote 6))
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