LOANS - Internal Loan and Preferred Equity Ratings (Details)	12 Months Ended
Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($)
Real Estate [Line Items]
Outstanding principal	$ 113,123,301,000	$ 96,602,237,000
Balance of the loan loss provision	20,100,000	3,500,000
Loan loss provision	16,569,000	3,496,000	$ 0
Commercial Mortgage
Real Estate [Line Items]
Outstanding principal	$ 1,627,109,000	$ 1,307,911,000
Percentage of CRE debt and preferred equity portfolio	100.00%	100.00%
Performing	$ 584,076,000	$ 793,842,000
Performing - closely monitored	649,216,000	254,676,000
Performing - special mention	240,014,000	151,400,000
Substandard	110,200,000	100,993,000
Doubtful	36,603,000	7,000,000
Loss	$ 7,000,000	$ 0
Commercial Mortgage \| Substandard
Real Estate [Line Items]
Number of rated loans \| loan	3	2
Commercial Mortgage \| Doubtful
Real Estate [Line Items]
Number of rated loans \| loan	1	1
Balance of the loan loss provision	$ 5,700,000
Loan loss provision		$ 3,500,000
Senior Mortgages \| Commercial Mortgage
Real Estate [Line Items]
Outstanding principal	$ 503,499,000	$ 988,248,000
Percentage of CRE debt and preferred equity portfolio	30.90%	75.60%
Performing	$ 94,711,000	$ 653,066,000
Performing - closely monitored	253,069,000	215,792,000
Performing - special mention	112,619,000	55,000,000
Substandard	43,100,000	64,390,000
Doubtful	0	0
Loss	0	0
Senior Securitized Mortgages \| Commercial Mortgage
Real Estate [Line Items]
Outstanding principal	$ 940,546,000	0
Percentage of CRE debt and preferred equity portfolio	57.80%
Performing	$ 429,209,000
Performing - closely monitored	333,942,000
Performing - special mention	127,395,000
Substandard	50,000,000
Doubtful	0
Loss	0
Mezzanine Loans \| Commercial Mortgage
Real Estate [Line Items]
Outstanding principal	$ 183,064,000	$ 319,663,000
Percentage of CRE debt and preferred equity portfolio	11.30%	24.40%
Performing	$ 60,156,000	$ 140,776,000
Performing - closely monitored	62,205,000	38,884,000
Performing - special mention	0	96,400,000
Substandard	17,100,000	36,603,000
Doubtful	36,603,000	7,000,000
Loss	$ 7,000,000	$ 0

Internal rate amount loss.

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Internal rating closely monitored loan.

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Internal rating doubtful loan.

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Internal rating special mention loan.

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Investments Owned, Number Of Rated Loans

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For investments which are quantified by principal amount, the principle balance held at close of period.

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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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