LOANS - Corporate Debt Held for Investment (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Principal payments	$ (621,804)
Sales	(2,728,213)
Corporate Loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	2,152,213
Beginning balance	2,144,850	$ 1,887,182
Originations & advances	678,608	888,036
Principal payments	(410,421)	(368,927)
Amortization & accretion of (premium) discounts	10,183	8,896
Loan restructuring	(16,732)
Sales	(312,250)	(262,974)
Net (increase) decrease in allowance		(7,363)
Allowance for loan losses
Current period allowance	(14,601)
Write offs	11,894
Ending allowance	(39,723)
Ending balance	2,061,878	2,144,850
Corporate Loans \| First lien loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	1,403,503
Beginning balance	1,396,140	1,346,356
Originations & advances	499,623	542,463
Principal payments	(311,856)	(228,302)
Amortization & accretion of (premium) discounts	6,826	5,960
Loan restructuring	(19,550)
Sales	(242,658)	(262,974)
Net (increase) decrease in allowance		(7,363)
Allowance for loan losses
Current period allowance	(9,517)
Write offs	11,894
Ending allowance	(15,773)
Ending balance	1,320,115	1,396,140
Corporate Loans \| Second lien loans
Financing Receivable, Allowance for Credit Loss [Line Items]
Beginning balance	748,710
Beginning balance	748,710	540,826
Originations & advances	178,985	345,573
Principal payments	(98,565)	(140,625)
Amortization & accretion of (premium) discounts	3,357	2,936
Loan restructuring	2,818
Sales	(69,592)	0
Net (increase) decrease in allowance		0
Allowance for loan losses
Current period allowance	(5,084)
Write offs	0
Ending allowance	(23,950)
Ending balance	741,763	748,710
Impact of adopting CECL \| Corporate Loans
Allowance for loan losses
Beginning allowance	(29,653)
Ending allowance		(29,653)
Impact of adopting CECL \| Corporate Loans \| First lien loans
Allowance for loan losses
Beginning allowance	(10,787)
Ending allowance		(10,787)
Impact of adopting CECL \| Corporate Loans \| Second lien loans
Allowance for loan losses
Beginning allowance	(18,866)
Ending allowance		(18,866)
CECL provision, adjusted balance \| Corporate Loans
Allowance for loan losses
Beginning allowance	(7,363)
Ending allowance		(7,363)
CECL provision, adjusted balance \| Corporate Loans \| First lien loans
Allowance for loan losses
Beginning allowance	(7,363)
Ending allowance		(7,363)
CECL provision, adjusted balance \| Corporate Loans \| Second lien loans
Allowance for loan losses
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

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
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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
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-Paragraph 2
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-Topic 230
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-Section 45
-Paragraph 28
-Subparagraph (b)
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Amount of allowance for credit loss for debt security measured at amortized cost (held-to-maturity).

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

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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

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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
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-SubTopic 310
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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

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-Publisher FASB
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-SubTopic 310
-Section S99
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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.

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