Accrued interest payable on construction loan.

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Debt instrument, maximum borrowing capacity.

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Development Costs - Contemplated Debt Financing

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Equity method investment summarized financial information debt.

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Equity method investment summarized financial information debt net.

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Net gain (loss) on real estate venture transactions including real estate venture formation.

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Number of unconsolidated investments in Real Estate Ventures.

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Number of units in real estate property sold.

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Sale of ownership interest percentage.

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Maturity date of mortgage loan within investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate, in CCYY-MM-DD format.

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Area of land held.

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Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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Net rentable area for properties owned.

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Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.

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The number of units in a real estate property owned as of the balance sheet date.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The cash outflow from repayment of borrowings to finance the cost of construction.

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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)				3 Months Ended		6 Months Ended
	Jun. 26, 2018 USD ($)	Jan. 10, 2018 USD ($) property	Jan. 05, 2018 USD ($) ft²	Jun. 30, 2018 USD ($) ft² a Real_Estate_Investment Apartment_unit	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) ft² a Real_Estate_Investment Apartment_unit	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method				$ 170,361,000		$ 170,361,000		$ 194,621,000
Accounts receivable				19,530,000		19,530,000		17,938,000
Debt, net				$ 641,351,000		$ 641,351,000		766,420,000
Area of real estate property \| ft²				16,462,764		16,462,764
Net gain on Real Estate Venture transactions				$ 0	$ 0	$ 37,263,000	$ 14,582,000
Proceeds from real estate venture sales						42,953,000	27,230,000
Evo at Cira Disposition [Member]
Schedule Of Equity Method Investments [Line Items]
Sale of ownership interest percentage		50.00%
Net gain on Real Estate Venture transactions		$ 25,700,000
Number of property units sold \| property		345
Sales Price		$ 197,500,000
Proceeds from real estate venture sales		43,000,000
Cost of equity method investment		17,300,000
Philadelphia [Member] \| Pennsylvania [Member] \| Evo at Cira Disposition [Member]
Schedule Of Equity Method Investments [Line Items]
Principal balance of secured loan		$ 110,900,000
Third Party Management Fees, Labor Reimbursement and Leasing [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees				$ 4,913,000	7,080,000	$ 12,587,000	13,565,000
Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet \| ft²				38,260		38,260
Area of real estate property \| ft²				14,966,602		14,966,602
Sales Price				$ 2,000,000		$ 2,000,000
Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Accounts receivable				1,300,000		1,300,000		$ 900,000
Real Estate Venture [Member] \| Third Party Management Fees, Labor Reimbursement and Leasing [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees				1,300,000	1,700,000	2,600,000	3,200,000
Real Estate Venture [Member] \| Lease Commission Income [Member] \| Third Party Management Fees, Labor Reimbursement and Leasing [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees				$ 1,500,000	$ 1,800,000	$ 2,900,000	$ 3,600,000
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment				10		10
Investment in Real Estate Ventures, equity method				$ 170,400,000		$ 170,400,000
Real estate ventures aggregate indebtedness				$ 645,500,000		$ 645,500,000
Unconsolidated Real Estate Ventures [Member] \| Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage				25.00%	20.00%	25.00%	20.00%
Unconsolidated Real Estate Ventures [Member] \| Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage				70.00%	70.00%	70.00%	70.00%
Unconsolidated Real Estate Ventures [Member] \| Six Real Estate Ventures [Member] \| Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment				6		6
Rentable Square Feet \| ft²				6,600,000		6,600,000
Unconsolidated Real Estate Ventures [Member] \| Two Real Estate Ventures [Member] \| Land Held For Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment				2		2
Acreage of land \| a				1.4		1.4
Unconsolidated Real Estate Ventures [Member] \| One Real Estate Venture [Member] \| Land Under Active Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment				1		1
Acreage of land \| a				1.3		1.3
Unconsolidated Real Estate Ventures [Member] \| One Other Real Estate Venture [Member] \| Residential Tower [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment				1		1
Number of Property units \| Apartment_unit				321		321
1919 Ventures
Schedule Of Equity Method Investments [Line Items]
Ownership percentage	50.00%
Debt, net	$ 44,400,000
Loan interest rate	4.00%
Mortgage loans scheduled maturity date	Jun. 25, 2023
Repayment of construction loan	$ 88,800,000
Construction loan, principal amount	88,600,000
Accrued interest on construction loan	$ 200,000
1919 Ventures \| LCOR/Calstrs [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage	50.00%
1919 Ventures \| Other Assets [Member]
Schedule Of Equity Method Investments [Line Items]
Note receivable	$ 44,400,000
Four Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage			35.00%
Net gain on Real Estate Venture transactions			$ 11,600,000
Four Tower Bridge [Member] \| Conshohocken [Member] \| Pennsylvania [Member]
Schedule Of Equity Method Investments [Line Items]
Area of real estate property \| ft²			86,021
Real estate property debt			$ 9,700,000
Seven Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Sale of ownership interest percentage			20.00%
PJP VII [Member]
Schedule Of Equity Method Investments [Line Items]
Real estate property debt				$ 4,200,000		$ 4,200,000
Guarantees, maximum exposure amount				400,000		400,000
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Guarantees, maximum exposure amount				41,300,000		41,300,000
Construction loan total borrowing capacity				$ 150,000,000		$ 150,000,000