INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - MAP Venture (Details) $ in Thousands			12 Months Ended
	Jan. 01, 2019 USD ($)	Aug. 01, 2018 USD ($)	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Feb. 04, 2016 ft²
Schedule of Equity Method Investments [Line Items]
Real estate ventures aggregate indebtedness to third parties			$ 596,007	$ 370,319
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%
Cumulative effect on retained earnings	$ 9,200		$ 4,600
Real estate ventures aggregate indebtedness to third parties		$ 180,800	$ 185,000	$ 185,000
Variable Interest Entity, Not Primary Beneficiary | MAP Venture
Schedule of Equity Method Investments [Line Items]
Number of office properties owned | property			58
Rentable square feet | ft²					3,924,783
Secured Debt | MAP Venture
Schedule of Equity Method Investments [Line Items]
Debt instrument, face amount		$ 185,000
Variable interest rate		2.45%
Maximum | Secured Debt | MAP Venture
Schedule of Equity Method Investments [Line Items]
Effective interest rate		6.00%