LOANS - Corporate Debt Held for Investment (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2021	Dec. 31, 2020
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Sales	$ (850,156)
Principal payments	(275,487)
Corporate Loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	2,239,930	$ 2,152,213
Originations & advances	71,493	1,061,644
Sales	(45,776)	(353,090)
Principal payments	(201,247)	(576,759)
Amortization & accretion of (premium) discounts	3,889	12,206
Loan restructuring		(16,732)
Allowance for loan losses
Beginning allowance	(39,552)
Current period (allowance) reversal	6,186	(14,429)
Write offs		11,893
Ending allowance	(33,366)	(39,552)
Carrying Value	2,074,475	2,239,930
Corporate Loans \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses
Beginning allowance		(29,653)
Corporate Loans \| Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses
Beginning allowance	(39,552)	(7,363)
Ending allowance		(39,552)
Corporate Loans \| First lien loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	1,489,125	1,403,503
Originations & advances	56,939	834,211
Sales	(21,328)	(273,887)
Principal payments	(96,247)	(444,759)
Amortization & accretion of (premium) discounts	1,708	8,374
Loan restructuring		(19,550)
Allowance for loan losses
Beginning allowance	(18,767)
Current period (allowance) reversal	1,685	(12,510)
Write offs		11,893
Ending allowance	(17,082)	(18,767)
Carrying Value	1,431,882	1,489,125
Corporate Loans \| First lien loans \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses
Beginning allowance		(10,787)
Corporate Loans \| First lien loans \| Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses
Beginning allowance	(18,767)	(7,363)
Ending allowance		(18,767)
Corporate Loans \| Second lien loans
SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward]
Beginning balance	750,805	748,710
Originations & advances	14,554	227,433
Sales	(24,448)	(79,203)
Principal payments	(105,000)	(132,000)
Amortization & accretion of (premium) discounts	2,181	3,832
Loan restructuring		2,818
Allowance for loan losses
Beginning allowance	(20,785)
Current period (allowance) reversal	4,501	(1,919)
Write offs		0
Ending allowance	(16,284)	(20,785)
Carrying Value	642,593	750,805
Corporate Loans \| Second lien loans \| Cumulative Effect, Period of Adoption, Adjustment
Allowance for loan losses
Beginning allowance		(18,866)
Corporate Loans \| Second lien loans \| Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for loan losses
Beginning allowance	$ (20,785)	0
Ending allowance		$ (20,785)

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

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=120402547&loc=d3e617274-123014

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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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Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

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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)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

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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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- 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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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
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
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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
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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
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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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