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Sale of ownership interest percentage.

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Area of land held.

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Net rentable area for properties owned.

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The number of real estate properties owned as of the balance sheet date.

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Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

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Investment in Unconsolidated Real Estate Ventures - Textual (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) a ft² investment property apartment	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) a ft² investment property apartment	Sep. 30, 2019 USD ($)	Jul. 21, 2020 USD ($) ft²	Dec. 31, 2019 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of properties \| property	92		92
Investment in Real Estate Ventures	$ 377,486		$ 377,486			$ 120,294
Accounts receivable	20,433		20,433			16,363
Debt, net	$ 1,919,511		$ 1,919,511			2,144,418
Minimum
Schedule of Equity Method Investments [Line Items]
Ownership percentage	15.00%		15.00%
Maximum
Schedule of Equity Method Investments [Line Items]
Ownership percentage	70.00%		70.00%
Real Estate Venture
Schedule of Equity Method Investments [Line Items]
Accounts receivable	$ 1,400		$ 1,400			800
Real Estate Venture \| Management Fees
Schedule of Equity Method Investments [Line Items]
Service and other revenue	1,300	$ 1,000	3,200	$ 3,200
Real Estate Venture \| Leasing Commission Income
Schedule of Equity Method Investments [Line Items]
Service and other revenue	200	$ 300	900	$ 800
Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Investment in Real Estate Ventures	$ 367,800		$ 367,800
Unconsolidated Real Estate Ventures \| Office properties
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| investment	4		4
Rentable area (in square feet) \| ft²	7,300,000		7,300,000
Unconsolidated Real Estate Ventures \| Unconsolidated Properties
Schedule of Equity Method Investments [Line Items]
Number of properties \| property	8		8
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 \| investment	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 \| investment	1		1
Area of land (in acres) \| a	1.3		1.3
Unconsolidated Real Estate Ventures \| Residential Tower
Schedule of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| investment	1		1
Number of apartment units (in units) \| apartment	321		321
One and Two Commerce Square
Schedule of Equity Method Investments [Line Items]
Ownership percentage	70.00%		70.00%
Secured Debt
Schedule of Equity Method Investments [Line Items]
Debt, net	$ 88,913		$ 88,913			$ 313,812
Secured Debt \| Philadelphia - Office
Schedule of Equity Method Investments [Line Items]
Debt, net					$ 222,100
Preferred Equity Securities \| One and Two Commerce Square
Schedule of Equity Method Investments [Line Items]
Ownership percentage	32.00%		32.00%
Common Equity Securities \| One and Two Commerce Square
Schedule of Equity Method Investments [Line Items]
Ownership percentage	38.00%		38.00%
Other Liabilities \| Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Investment in Real Estate Ventures	$ (9,700)		$ (9,700)
One and Two Commerce Square
Schedule of Equity Method Investments [Line Items]
Sale of ownership interest percentage					30.00%
One and Two Commerce Square \| Office properties
Schedule of Equity Method Investments [Line Items]
Rentable area (in square feet) \| ft²					1,896,142