REAL ESTATE HELD FOR INVESTMENT - Highest Tenant Industry Concentrations - Greater than 10% of Annual Base Rent (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) tenant
Concentration Risk [Line Items]
Number of tenants | tenant	300
Annualized Base Rent | $	$ 34,717
Industry | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	53.50%
Computer Systems Design
Concentration Risk [Line Items]
Number of tenants | tenant	30
Annualized Base Rent | $	$ 7,080
Computer Systems Design | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	10.90%
Professional, Scientific, and Technical Services
Concentration Risk [Line Items]
Number of tenants | tenant	42
Annualized Base Rent | $	$ 7,078
Professional, Scientific, and Technical Services | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	10.90%
Public Administration
Concentration Risk [Line Items]
Number of tenants | tenant	11
Annualized Base Rent | $	$ 6,959
Public Administration | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	10.70%
Insurance Carriers and Related Activities
Concentration Risk [Line Items]
Number of tenants | tenant	16
Annualized Base Rent | $	$ 6,801
Insurance Carriers and Related Activities | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	10.50%
Health Care and Social Assistance
Concentration Risk [Line Items]
Number of tenants | tenant	25
Annualized Base Rent | $	$ 6,799
Health Care and Social Assistance | Industry | Revenue Benchmark
Concentration Risk [Line Items]
Percentage of Annualized Base Rent	10.50%