INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Austin Venture (Details) $ in Thousands				12 Months Ended
	Dec. 11, 2018 USD ($) ft² property	Oct. 18, 2017 USD ($) ft² property	Oct. 17, 2017 USD ($) property	Dec. 31, 2019 USD ($) ft² property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Oct. 16, 2013 USD ($) ft² property
Schedule of Equity Method Investments [Line Items]
Area of real estate property | ft²				16,711,387
Real estate ventures aggregate indebtedness to third parties				$ 596,007	$ 370,319
Net gain on real estate venture transactions				$ 11,639	$ 142,233	$ 80,526
Number of Properties | property				95
Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Ownership percentage		50.00%
Number of properties sold | property		8	7
Rentable square feet | ft²		1,164,496
Gross sales price		$ 333,250
Real estate ventures aggregate indebtedness to third parties		150,968	$ 151,000
Proceeds from divestiture of businesses, net of cash divested		86,400
Net gain on real estate venture transactions		40,092
Deferred gain on sale		$ 12,072
Brandywine Realty Trust
Schedule of Equity Method Investments [Line Items]
Ownership percentage				50.00%
Equity method investment, additional distribution rights				10.00%
Brandywine Realty Trust | Austin Joint Venture
Schedule of Equity Method Investments [Line Items]
Number of properties contributed to a joint venture | property									7
Area of real estate property | ft²									1,398,826
Aggregate gross sales price of a joint venture									$ 330,000
Equity method investment, agreement to pay future capital expenditures							$ 4,400	$ 800	$ 5,200
DRA Advisors LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage				50.00%
DRA Austin Venture
Schedule of Equity Method Investments [Line Items]
Area of real estate property | ft²	1,570,123
Ownership percentage	50.00%
Net gain on real estate venture transactions	$ 103,800
Aggregate purchase price	$ 535,100
Number of Properties | property	12