INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - MAP Venture (Details) $ in Thousands		12 Months Ended
	Aug. 01, 2018 USD ($)	Dec. 31, 2020 USD ($) ft² property	Dec. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Real estate ventures aggregate indebtedness to third parties		$ 963,018	$ 596,007
MAP Venture
Schedule of Equity Method Investments [Line Items]
Ground lease annual payments		$ 11,900
Ground lease annual rent expense increase percentage through November 2025		2.50%
Ground lease annual rent expense increase after November 2025		2.50%
Real estate ventures aggregate indebtedness to third parties	$ 180,800	$ 185,000	185,000
MAP Venture | Variable Interest Entity, Not Primary Beneficiary
Schedule of Equity Method Investments [Line Items]
Number of office properties owned | property		58
Rentable square feet | ft²		3,924,783
MAP Venture | Cumulative Effect, Period of Adoption, Adjustment
Schedule of Equity Method Investments [Line Items]
Retained earnings			$ 4,600	$ 9,200
Secured Debt | MAP Venture
Schedule of Equity Method Investments [Line Items]
Debt instrument, face amount	$ 185,000
Variable interest rate	2.45%