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INVESTMENT IN UNCONSOLIDATED REAL ESTATE VENTURES - Brandywine - AI Venture (Details)		12 Months Ended
	Nov. 09, 2021 USD ($) ft²	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) ft²
Schedule of Equity Method Investments [Line Items]
Net gain on real estate venture transactions		$ 2,973,000	$ 75,000	$ 11,639,000
Impairment of properties held for use		0	$ 0	0
Brandywine - AI Venture LLC \| Fairview Properties
Schedule of Equity Method Investments [Line Items]
Provision for impairment on assets held for sale		1,400,000
Impairment of properties held for use				5,600,000
Brandywine - AI Venture LLC \| Fairview Properties \| Brandywine Realty Trust
Schedule of Equity Method Investments [Line Items]
Provision for impairment on assets held for sale		$ 700,000
Impairment of properties held for use				$ 2,800,000
Brandywine - AI Venture LLC \| Falls Church, Virginia
Schedule of Equity Method Investments [Line Items]
Rentable square feet \| ft²	183,618			180,659
Aggregate sales price	$ 27,600,000
Gross proceeds from sale	12,600,000
Net gain on real estate venture transactions	$ 3,000,000			$ 2,200,000
Debt, net				$ 26,000,000