Investment in Unconsolidated Real Estate Ventures - Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss) (Parenthetical) (Details) $ in Thousands			12 Months Ended
		Mar. 02, 2016 USD ($) option term	Dec. 31, 2016 USD ($)		Sep. 22, 2016	Jun. 30, 2016	Dec. 31, 2015 USD ($)	Jun. 22, 2015	Dec. 20, 2011	Jan. 20, 2011
Schedule Of Equity Method Investments [Line Items]
Notional amount			$ 328,610				$ 328,610
Equity Method Investment Summarized Financial Information Debt			$ 997,466				794,571
Brandywine - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage			50.00%	[1],[2]					50.00%
Debt Instrument, Interest Rate, Effective Percentage	[2]		3.96%
Equity Method Investment Summarized Financial Information Debt	[2]		$ 131,539				132,717
HSRE BDN I, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[1],[3]		50.00%
Equity Method Investment Summarized Financial Information Debt	[3]		$ 105,000				95,562
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[1],[4]		50.00%
Debt Instrument, Interest Rate, Effective Percentage	[4]		3.36%
Equity Method Investment Summarized Financial Information Debt	[4]		$ 405,734				410,066
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[1],[5]		50.00%
Equity Method Investment Summarized Financial Information Debt	[5]		$ 180,800				0
PJP V [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage					25.00%
Equity Method Investment Summarized Financial Information Debt	[6]		0				5,035
1000 Chesterbrook Blvd. [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage						50.00%
Equity Method Investment Summarized Financial Information Debt	[6]		0				23,610
Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Percentage of ownership interests								50.00%
Equity Method Investment Summarized Financial Information Debt	[6]		$ 0				0
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage			50.00%	[1],[4],[7]						50.00%
Debt Instrument, Interest Rate Terms			LIBOR + 2.00
Interest rate protection cap			4.50%
Interest rate upon 90% residential occupancy and commencement of lease in retail space			1.75%
Percentage of residential occupancy and commencement of lease in retail space			90.00%
Equity Method Investment Summarized Financial Information Debt	[4],[7]		$ 79,250				19,411
Seven Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage	[1]		20.00%
Debt Instrument, Interest Rate, Effective Percentage			3.71%
Equity Method Investment Summarized Financial Information Debt			$ 14,710				$ 14,789
Secured JV Debt [Member] | Brandywine - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Number of Fixed Rate Mortgages			3
Secured JV Debt [Member] | Brandywine - Al Venture [Member] | Fixed rate loan maturing January 1, 2019 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 37,900
Debt Instrument, Interest Rate, Stated Percentage			4.40%
Debt Instrument Maturity Date			Jan. 01, 2019
Secured JV Debt [Member] | Brandywine - Al Venture [Member] | Fixed rate loan maturing January 1, 2022 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 27,100
Debt Instrument, Interest Rate, Stated Percentage			4.65%
Debt Instrument Maturity Date			Jan. 01, 2022
Secured JV Debt [Member] | Brandywine - Al Venture [Member] | Fixed rate loan maturing August 1, 2019 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 66,500
Debt Instrument, Interest Rate, Stated Percentage			3.22%
Debt Instrument Maturity Date			Aug. 01, 2019
Long-term Debt, Weighted Average Interest Rate			3.96%
Secured JV Debt [Member] | HSRE BDN I, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage		50.00%
Secured JV Debt [Member] | Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Number of Mortgages			7
Secured JV Debt [Member] | Austin Joint Venture [Member] | First mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 33,900
Debt Instrument Maturity Date			Nov. 01, 2018
Derivative, Fixed Interest Rate			1.59%
Debt Instrument, Interest Rate, Effective Percentage			3.52%
Derivative, Basis Spread on Variable Rate			1.93%
Secured JV Debt [Member] | Austin Joint Venture [Member] | Second mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 54,700
Debt Instrument Maturity Date			Oct. 15, 2018
Derivative, Fixed Interest Rate			1.49%
Debt Instrument, Interest Rate, Effective Percentage			3.19%
Derivative, Basis Spread on Variable Rate			1.70%
Secured JV Debt [Member] | Austin Joint Venture [Member] | Third mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 137,000
Debt Instrument Maturity Date			Nov. 01, 2018
Derivative, Fixed Interest Rate			1.43%
Debt Instrument, Interest Rate, Effective Percentage			3.44%
Derivative, Basis Spread on Variable Rate			2.01%
Secured JV Debt [Member] | Austin Joint Venture [Member] | Fourth mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 29,000
Debt Instrument, Interest Rate, Stated Percentage			4.50%
Debt Instrument Maturity Date			Apr. 06, 2019
Secured JV Debt [Member] | Austin Joint Venture [Member] | Fifth mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 34,300
Debt Instrument, Interest Rate, Stated Percentage			3.87%
Debt Instrument Maturity Date			Aug. 06, 2019
Secured JV Debt [Member] | Austin Joint Venture [Member] | Sixth mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 86,700
Debt Instrument Maturity Date			Feb. 10, 2020
Derivative, Fixed Interest Rate			1.36%
Debt Instrument, Interest Rate, Effective Percentage			3.36%
Derivative, Basis Spread on Variable Rate			2.00%
Secured JV Debt [Member] | Austin Joint Venture [Member] | Seventh mortgage - swapped to fixed [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Face Amount			$ 30,000
Debt Instrument Maturity Date			Jan. 01, 2021
Long-term Debt, Weighted Average Interest Rate			3.36%
Debt Instrument, Interest Rate Terms			LIBOR + 1.85
Interest rate protection cap			2.75%
Secured JV Debt [Member] | MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument Maturity Date			Feb. 09, 2018
Interest rate protection cap		1.75%
Notional amount		$ 200,800
Debt instrument, number of options to extend maturity date | option		3
Debt instrument, number of successive terms | term		3
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Mortgage Maturing March 2017 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.00%
Debt Instrument Maturity Date			Mar. 01, 2017
Debt Instrument, Number of Fixed Rate Mortgages			2
Equity Method Investment Summarized Financial Information Debt			$ 8,000
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing September 2025 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.00%
Debt Instrument Maturity Date			Sep. 01, 2025
Equity Method Investment Summarized Financial Information Debt			$ 800
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing February 2017 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			4.00%
Debt Instrument Maturity Date			Feb. 07, 2017
Equity Method Investment Summarized Financial Information Debt			$ 2,000
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing March 2020 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			3.25%
Debt Instrument Maturity Date			Mar. 11, 2020
Long-term Debt, Weighted Average Interest Rate			3.42%
Equity Method Investment Summarized Financial Information Debt			$ 3,900

[1] Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.

[2] See “Brandywine AI Venture: 3141 Fairview Park Drive” section below for information discussing activity that occurred during 2016 relating to this venture.

[3] The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “Evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “Evo at Cira South Venture” section below for further details on these transactions

[4] The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “Evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “Evo at Cira South Venture” section below for further details on these transactions.

[5] In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.

[6] The Company liquidated its 25% ownership interest in the PJP V real estate venture on September 22, 2016. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. The Company purchased the remaining 50% interest in Broadmoor Austin Associates on June 22, 2015. The ownership interest in Residence Inn Tower Bridge was sold on December 30, 2015. See below for further detail on 2016 dispositions.

[7] The stated rate for the construction loan is LIBOR + 2.00%. It is further reduced to 1.75% upon reaching 90% residential occupancy and commencement of the lease in the retail space. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%.