LOANS - CRE Debt and Preferred Equity Investments - Based on Outstanding Principal (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Real Estate [Roll Forward]
Principal payments	$ (726,064)
Ending balance, carrying value	669,713
Commercial Mortgage
Real Estate [Roll Forward]
Beginning balance, carrying value	1,296,803	$ 1,029,327
Originations & advances (principal)	593,913	628,177
Principal payments	(316,663)	(353,424)
Transfers	40,058
Net (increase) decrease in origination fees	(4,384)	(6,994)
Amortization of net origination fees	5,571	3,213
Allowance for loan losses	(9,207)	(3,496)
Ending balance, carrying value	1,606,091	1,296,803
Commercial Mortgage \| Senior Mortgages
Real Estate [Roll Forward]
Beginning balance, carrying value	981,202	625,900
Originations & advances (principal)	572,204	575,953
Principal payments	(16,785)	(216,849)
Transfers	(1,034,754)
Net (increase) decrease in origination fees	(4,200)	(6,624)
Amortization of net origination fees	2,023	2,822
Allowance for loan losses	0	0
Ending balance, carrying value	499,690	981,202
Commercial Mortgage \| Senior Securitized Mortgages
Real Estate [Roll Forward]
Beginning balance, carrying value	0
Originations & advances (principal)	0
Principal payments	(150,245)
Transfers	1,083,487
Net (increase) decrease in origination fees	0
Amortization of net origination fees	3,136
Allowance for loan losses	0
Ending balance, carrying value	936,378	0
Commercial Mortgage \| Preferred Equity
Real Estate [Roll Forward]
Beginning balance, carrying value	0	8,985
Originations & advances (principal)		0
Principal payments		(9,000)
Net (increase) decrease in origination fees		0
Amortization of net origination fees		15
Allowance for loan losses		0
Ending balance, carrying value		0
Mezzanine Loans \| Commercial Mortgage
Real Estate [Roll Forward]
Beginning balance, carrying value	315,601	394,442
Originations & advances (principal)	21,709	52,224
Principal payments	(149,633)	(127,575)
Transfers	(8,675)
Net (increase) decrease in origination fees	(184)	(370)
Amortization of net origination fees	412	376
Allowance for loan losses	(9,207)	(3,496)
Ending balance, carrying value	$ 170,023	$ 315,601

(Increase) Decrease in Lease Origination Costs

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- Definition

Mortgage Loans on Real Estate, Change In Loan Loss Allowance

+ References

No definition available.

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Mortgage Loans on Real Estate, Transfers

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Real Estate [Roll Forward]

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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

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
-URI http://asc.fasb.org/extlink&oid=109123272&loc=d3e8622-111531

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)
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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 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))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

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