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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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For an unclassified balance sheet, the amount due from customers or clients for goods or services that have been delivered or sold in the normal course of business, reduced to their estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Area of land held.

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Area of a real estate property.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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

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This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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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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Revenue, comprised of base and incentive revenue derived from the management of joint ventures, managing third-party properties, or another entity's operations.

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Net rentable area for properties owned.

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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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Investment in Unconsolidated Real Estate Ventures (Textual) (Details)			3 Months Ended
	Jan. 10, 2018 USD ($) property	Jan. 05, 2018 USD ($) ft²	Mar. 31, 2018 USD ($) ft² a Real_Estate_Investment Apartment_unit	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method			$ 171,383,000		$ 194,621,000
Management fees			7,674,000	$ 6,485,000
Accounts receivable			$ 17,794,000		17,938,000
Area of real estate property \| ft²			16,501,024
Net gain on Real Estate Venture transactions			$ 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
Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Area of real estate property \| ft²			15,004,862
Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees			$ 1,300,000	1,500,000
Accounts receivable			1,400,000		$ 900,000
Real Estate Venture [Member] \| Lease Commission Income [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees			$ 800,000	$ 1,300,000
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures \| Real_Estate_Investment			10
Investment in Real Estate Ventures, equity method			$ 171,400,000
Real estate ventures aggregate indebtedness to third parties			$ 639,300,000
Unconsolidated Real Estate Ventures [Member] \| Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage			25.00%	20.00%
Unconsolidated Real Estate Ventures [Member] \| Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage			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
Rentable Square Feet \| ft²			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
Acreage of land \| a			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
Acreage of land \| a			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
Number of Property units \| Apartment_unit			321
Four Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment 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			$ 4,300,000
Guarantees, maximum exposure amount			400,000
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Guarantees, maximum exposure amount			41,300,000
Loan total borrowing capacity			$ 150,000,000