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Investment in Unconsolidated Real Estate Ventures - Textual (Details) $ in Thousands		3 Months Ended		9 Months Ended
	Feb. 02, 2021 USD ($)	Sep. 30, 2021 USD ($) a ft² property apartment	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) a ft² property apartment	Sep. 30, 2020 USD ($)	Jul. 23, 2021 USD ($)	Feb. 02, 2021 ft²	Feb. 02, 2021 a	Feb. 02, 2021	Dec. 31, 2020 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of real estate properties \| property		81		81
Investment in unconsolidated real estate ventures		$ 449,658		$ 449,658						$ 401,327
Accounts receivable		11,645		11,645						13,536
Investment in real estate ventures		$ 427,411		$ 427,411						389,811
Brandywine Al Venture L L C \| Fairview Properties
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%		50.00%
Impairment charge		$ 1,100
Brandywine Al Venture L L C \| Fairview Properties \| Brandywine Realty Trust
Schedule of Equity Method Investments [Line Items]
Impairment charge		600
3025 JFK Venture
Schedule of Equity Method Investments [Line Items]
Area of land (in acres)							1	1
Equity method investment, ownership percentage									55.00%
Lease agreement term	99 years
Investment in real estate ventures	$ 34,800
Area of building to be constructed \| ft²							570,000
Estimated project cost	287,300
Joint venture, funding committed by other party	$ 45,200
Ownership interest held by partner									45.00%
Joint venture, funding committed		20,500		$ 20,500
Construction loan amount						$ 186,700
3025 JFK Venture \| LIBOR
Schedule of Equity Method Investments [Line Items]
Construction loan, interest rate						3.50%
Interest rate, floor						0.25%
Real Estate Venture
Schedule of Equity Method Investments [Line Items]
Accounts receivable		2,000		2,000						$ 1,200
Management Fees \| Real Estate Venture
Schedule of Equity Method Investments [Line Items]
Service and other revenue		2,100	$ 1,300	6,200	$ 3,200
Leasing Commission Income \| Real Estate Venture
Schedule of Equity Method Investments [Line Items]
Service and other revenue		$ 700	$ 200	$ 2,600	$ 900
Minimum
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		15.00%		15.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		70.00%		70.00%
Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated real estate ventures		$ 427,400		$ 427,400
Unconsolidated Real Estate Ventures \| Office properties
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| property		5		5
Rentable area (in square feet) \| ft²		8,400,000		8,400,000
Unconsolidated Real Estate Ventures \| Other Liabilities
Schedule of Equity Method Investments [Line Items]
Investment in unconsolidated real estate ventures		$ 22,200		$ 22,200
Unconsolidated Real Estate Ventures \| Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Number of real estate properties \| property		10		10
Number of properties with negative investment balances \| property		1		1
Unconsolidated Real Estate Ventures \| Land Held For Development
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| property		2		2
Area of land (in acres) \| a		1.4		1.4
Unconsolidated Real Estate Ventures \| Land Under Active Development
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| property		1		1
Area of land (in acres) \| a		1.0		1.0
Unconsolidated Real Estate Ventures \| Mixed Use Tower
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| property		1		1
Rentable area (in square feet) \| ft²		200,000		200,000
Number of apartment units (in units) \| apartment		250		250
Unconsolidated Real Estate Ventures \| Residential Tower
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| property		1		1
Number of apartment units (in units) \| apartment		321		321