REAL ESTATE HELD FOR INVESTMENT - Properties Represented More than 10% of Company’s Total Assets (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($) ft² $ / ft²	Dec. 31, 2020 USD ($)
Real Estate Properties [Line Items]
Rentable Square Feet | ft²	7,300,000
Total Real Estate, Net	$ 1,922,659	$ 2,028,943
Annualized Base Rent	$ 66,584
Occupancy	85.00%
Accenture Tower | Assets, Total
Real Estate Properties [Line Items]
Rentable Square Feet | ft²	1,457,724
Total Real Estate, Net	$ 366,144
Annualized Base Rent	$ 28,204
Average Annualized Base Rent per sq. ft. | $ / ft²	26.55
Occupancy	72.90%
Accenture Tower | Assets, Total | Customer Concentration Risk
Real Estate Properties [Line Items]
Percentage of Total Assets	15.60%