REAL ESTATE HELD FOR INVESTMENT - Highest Tenant Industry Concentrations - Greater than 10% of Annual Base Rent (Details) $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($) tenant
Concentration Risk [Line Items]
Number of tenants \| tenant	235
Annualized Base Rent \| $	$ 21,113
Percentage of Annualized Base Rent	34.30%
Insurance
Concentration Risk [Line Items]
Number of tenants \| tenant	25
Annualized Base Rent \| $	$ 7,256
Percentage of Annualized Base Rent	11.80%
Computer Systems Design
Concentration Risk [Line Items]
Number of tenants \| tenant	25
Annualized Base Rent \| $	$ 7,088
Percentage of Annualized Base Rent	11.50%
Health Care and Social Assistance
Concentration Risk [Line Items]
Number of tenants \| tenant	15
Annualized Base Rent \| $	$ 6,769
Percentage of Annualized Base Rent	11.00%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13531-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13537-108611

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration