REAL ESTATE HELD FOR INVESTMENT - Concentration Risk (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020 USD ($) ft² tenant extension $ / ft²
Concentration Risk [Line Items]
Number of tenants	60
Customer Concentration Risk
Concentration Risk [Line Items]
Annualized base rent | $	$ 2.9
Average Annualized Base Rent per sq. ft. | $ / ft²	21.37
Customer Concentration Risk | Expires on December 31, 2024
Concentration Risk [Line Items]
Extension options | extension	2
Extension period	5 years
Customer Concentration Risk | Annualized Rent
Concentration Risk [Line Items]
Number of tenants	1
Concentration risk, percentage	22.00%
Customer Concentration Risk | Rentable Square Feet
Concentration Risk [Line Items]
Concentration risk, percentage	23.00%
Net rentable area | ft²	135,727