RELATED PARTY TRANSACTIONS - Real Estate Property Co-Management Agreements (Details) - KBS Management Group, LLC	6 Months Ended
	Jun. 30, 2020
Related Party Transaction [Line Items]
Initial term of management agreements	1 year
Successive periods, renewal	1 year
Period of termination notice	30 days
Period of termination notice with cause	5 days
Von Karman Tech Center
Related Party Transaction [Line Items]
Annual fee percentage	1.50%
Commonwealth Building
Related Party Transaction [Line Items]
Annual fee percentage	1.25%
The Offices at Greenhouse
Related Party Transaction [Line Items]
Annual fee percentage	0.25%
Institute Property
Related Party Transaction [Line Items]
Annual fee percentage	1.00%