Investment in Unconsolidated Real Estate Ventures - Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Sep. 22, 2016	Jun. 30, 2016	Jan. 29, 2016	Dec. 30, 2015	May 29, 2015	Dec. 20, 2011	Jan. 20, 2011
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method		$ 281,331		$ 241,004		$ 225,004
Equity Method Investments including net liabilities				239,874
Company’s share of income (loss) (Company’s basis)		(11,503)		(811)		$ (790)
Equity Method Investment Summarized Financial Information Debt		$ 997,466		794,571
Brandywine - AI Venture LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%	[1],[2]									50.00%
Investment in Real Estate Ventures, equity method	[2]	$ 67,809		50,760
Company’s share of income (loss) (Company’s basis)	[2]	(5,895)		(229)
Equity Method Investment Summarized Financial Information Debt	[2]	$ 131,539		132,717
Debt Instrument, Interest Rate, Effective Percentage	[2]	3.96%
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1],[3]	50.00%
Investment in Real Estate Ventures, equity method	[3]	$ 52,886		60,427
Company’s share of income (loss) (Company’s basis)	[3]	(1,880)		(1,235)
Equity Method Investment Summarized Financial Information Debt	[3]	$ 405,734		410,066
Debt Instrument, Interest Rate, Effective Percentage	[3]	3.36%
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1],[4]	50.00%
Investment in Real Estate Ventures, equity method	[4]	$ 20,893		0
Company’s share of income (loss) (Company’s basis)	[4]	(4,218)		0
Equity Method Investment Summarized Financial Information Debt	[4]	$ 180,800		0
Debt Instrument, Interest Rate Terms	[4]	L+6.25%
Debt Instrument, Maturity Date, Month and Year	[4]	2018-02
Four Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	65.00%
Investment in Real Estate Ventures, equity method		$ 2,286		1,684
Company’s share of income (loss) (Company’s basis)		602		211
Equity Method Investment Summarized Financial Information Debt		$ 9,961		10,162
Debt Instrument, Interest Rate, Effective Percentage		5.20%
Debt Instrument, Maturity Date, Month and Year		2021-02
PJP VII [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	25.00%
Investment in Real Estate Ventures, equity method		$ 980		872
Company’s share of income (loss) (Company’s basis)		233		211
Equity Method Investment Summarized Financial Information Debt		$ 4,956		5,621
Debt Instrument, Interest Rate Terms		L+2.65%
Debt Instrument, Maturity Date, Month and Year		2019-12
PJP Two [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	30.00%
Investment in Real Estate Ventures, equity method		$ 532		435
Company’s share of income (loss) (Company’s basis)		97		32
Equity Method Investment Summarized Financial Information Debt		$ 2,893		3,201
Debt Instrument, Interest Rate, Effective Percentage		6.12%
Debt Instrument, Maturity Date, Month and Year		2023-11
PJP VI [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	25.00%
Investment in Real Estate Ventures, equity method		$ 142		45
Company’s share of income (loss) (Company’s basis)		97		151
Equity Method Investment Summarized Financial Information Debt		$ 7,652		7,918
Debt Instrument, Interest Rate, Effective Percentage		6.08%
Debt Instrument, Maturity Date, Month and Year		2023-04
1000 Chesterbrook Blvd. [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage								50.00%
Investment in Real Estate Ventures, equity method	[5]	$ 0		1,895
Company’s share of income (loss) (Company’s basis)	[5]	160		117
Equity Method Investment Summarized Financial Information Debt	[5]	0		23,610
PJP V [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage							25.00%
Investment in Real Estate Ventures, equity method	[5]	0		305
Company’s share of income (loss) (Company’s basis)	[5]	127		189
Equity Method Investment Summarized Financial Information Debt	[5]	0		5,035
Invesco, L.P. [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[5]	0		0
Company’s share of income (loss) (Company’s basis)	[5]	261		349
Equity Method Investment Summarized Financial Information Debt	[5]	0		0
Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[5]	0		0
Company’s share of income (loss) (Company’s basis)	[5]	0		(377)
Equity Method Investment Summarized Financial Information Debt	[5]	0		0
Coppell Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage									50.00%
Investment in Real Estate Ventures, at equity	[6]	0		(1,130)
Company’s share of income (loss) (Company’s basis)	[6]	12		84
Equity Method Investment Summarized Financial Information Debt	[6]	$ 0		15,515
HSRE BDN I, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1],[7]	50.00%
Investment in Real Estate Ventures, equity method	[7]	$ 21,228		15,003
Company’s share of income (loss) (Company’s basis)	[7]	843		(188)
Equity Method Investment Summarized Financial Information Debt	[7]	$ 105,000		95,562
Debt Instrument, Interest Rate Terms	[7]	L+2.25%
Debt Instrument, Maturity Date, Month and Year	[7]	2019-10
TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	50.00%
Investment in Real Estate Ventures, equity method		$ 12,450		12,338
Company’s share of income (loss) (Company’s basis)		119		(252)
Equity Method Investment Summarized Financial Information Debt		$ 53,967		50,964
Debt Instrument, Interest Rate Terms		L+1.70%
Debt Instrument, Maturity Date, Month and Year		2017-12
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%	[1],[3],[8]										50.00%
Investment in Real Estate Ventures, equity method	[3],[8]	$ 27,462		29,086
Company’s share of income (loss) (Company’s basis)	[3],[8]	(1,529)		0
Equity Method Investment Summarized Financial Information Debt	[3],[8]	$ 79,250		19,411
Debt Instrument, Interest Rate Terms	[3],[8]	L+2.00%
Debt Instrument, Maturity Date, Month and Year	[3],[8]	2018-10
Residence Inn Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage										50.00%
Investment in Real Estate Ventures, equity method		$ 0	[5]	0	[5]					$ 900
Company’s share of income (loss) (Company’s basis)	[5]	0		367
Equity Method Investment Summarized Financial Information Debt	[5]	$ 0		0
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	50.00%
Investment in Real Estate Ventures, equity method		$ 36,356		36,626
Company’s share of income (loss) (Company’s basis)		(270)		(106)
Equity Method Investment Summarized Financial Information Debt		$ 1,004		0
Debt Instrument, Interest Rate Terms		L+2.40%
Debt Instrument, Maturity Date, Month and Year		2019-03
51 N 50 Patterson [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		70.00%	[1]								70.00%
Investment in Real Estate Ventures, equity method		$ 20,318		16,725
Company’s share of income (loss) (Company’s basis)		(114)		0
Equity Method Investment Summarized Financial Information Debt		$ 0		0
1250 First Street Office [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		70.00%	[1]								70.00%
Investment in Real Estate Ventures, equity method		$ 17,304		14,312
Company’s share of income (loss) (Company’s basis)		(15)		0
Equity Method Investment Summarized Financial Information Debt		$ 0		0
Seven Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	[1]	20.00%
Investment in Real Estate Ventures, equity method		$ 685		491
Company’s share of income (loss) (Company’s basis)		(133)		(135)
Equity Method Investment Summarized Financial Information Debt		$ 14,710		$ 14,789
Debt Instrument, Interest Rate, Effective Percentage		3.71%

[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] 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.

[5] 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.

[6] Carrying amount represents the negative investment balance of the venture that was included in other liabilities as of December 31, 2015. The ownership interest in this venture was disposed of on January 29, 2016.

[7] 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

[8] 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%.