REAL ESTATE HELD FOR INVESTMENT - Highest Tenant Industry Concentrations - Greater than 10% of Annual Base Rent (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) tenant
Concentration Risk [Line Items]
Number of tenants | tenant	239
Annualized Base Rent | $	$ 21,349
Percentage of Annualized Base Rent	36.30%
Computer Systems Design
Concentration Risk [Line Items]
Number of tenants | tenant	26
Annualized Base Rent | $	$ 7,395
Percentage of Annualized Base Rent	12.60%
Insurance
Concentration Risk [Line Items]
Number of tenants | tenant	25
Annualized Base Rent | $	$ 7,185
Percentage of Annualized Base Rent	12.20%
Health Care and Social Assistance
Concentration Risk [Line Items]
Number of tenants | tenant	15
Annualized Base Rent | $	$ 6,769
Percentage of Annualized Base Rent	11.50%