COMMERCIAL REAL ESTATE INVESTMENTS - CRE Debt and Preferred Equity Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate [Line Items]
Carrying Value	$ 1,029,327	$ 970,505	$ 1,348,817
Carrying value, unamortized origination fees	3,800	4,500
Preferred equity
Real Estate [Line Items]
Carrying Value	8,985	8,967	121,773
Commercial Mortgage
Real Estate [Line Items]
Outstanding Principal	1,033,158	975,015
Carrying Value	$ 1,029,327	$ 970,505
Percentage of Loan Portfolio	100.00%	100.00%
Commercial Mortgage \| Mezzanine loans
Real Estate [Line Items]
Outstanding Principal	$ 395,015	$ 453,693
Carrying Value	$ 394,442	$ 451,467	578,503
Percentage of Loan Portfolio	38.20%	46.50%
Commercial Mortgage \| Senior mortgages
Real Estate [Line Items]
Outstanding Principal	$ 629,143	$ 512,322
Carrying Value	$ 625,900	$ 510,071	$ 385,838
Percentage of Loan Portfolio	60.90%	52.60%
Commercial Mortgage \| Preferred equity
Real Estate [Line Items]
Outstanding Principal	$ 9,000	$ 9,000
Carrying Value	$ 8,985	$ 8,967
Percentage of Loan Portfolio	0.90%	0.90%

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 6
-Subparagraph (SX 210.12-14.Column B)
-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

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-Publisher FASB
-Name Accounting Standards Codification
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Percent of net assets at close of period. For schedules of investments that are categorized, each category has a percent of net assets for the aggregated value of the Investments in the category.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 210
-Section 50
-Paragraph 6
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-URI http://asc.fasb.org/extlink&oid=63488139&loc=d3e12121-115841

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

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The carrying amount of the outstanding balance due under the mortgage loan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Section S99
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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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