Investment in Unconsolidated Ventures - Investment in Real Estate Ventures and Share of Real Estate Ventures' Income (Loss) (Parenthetical) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Jun. 22, 2015	Dec. 31, 2014
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		0.00%
Equity Method Investment Summarized Financial Information Debt		$ 794,571		$ 965,077
Brandywine - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		3.94%
Equity Method Investment Summarized Financial Information Debt		$ 132,717		133,843
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	[1]	3.38%
Equity Method Investment Summarized Financial Information Debt	[1]	$ 410,066		382,100
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate Terms		LIBOR + 2.25
Interest rate protection cap		4.50%
Interest rate upon receipt of certificate of occupancy		2.00%
Interest rate upon stabilization		1.75%
Equity Method Investment Summarized Financial Information Debt	[1],[2]	$ 19,411		0
Seven Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Effective Percentage		3.44%
Equity Method Investment Summarized Financial Information Debt		$ 14,789		14,865
Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	[3]	0.00%
Equity Method Investment Summarized Financial Information Debt	[3]	$ 0		$ 53,516
Percentage of ownership interests			50.00%
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		$ 38,800
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		$ 27,600
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		3.94%
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		$ 34,000
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		$ 55,800
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		$ 140,300
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		$ 34,500
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		$ 86,400
Debt Instrument Maturity Date		Feb. 28, 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
Long-term Debt, Weighted Average Interest Rate		3.38%
Debt Instrument, Interest Rate Terms		LIBOR + 1.85
Interest rate protection cap		2.75%
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		$ 900
Secured JV Debt [Member] | Seven Tower Bridge [Member] | Fixed Rate Loan Maturing February 2016 [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.00%
Debt Instrument Maturity Date		Feb. 07, 2016
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		3.00%
Debt Instrument Maturity Date		Mar. 11, 2020
Long-term Debt, Weighted Average Interest Rate		3.40%
Equity Method Investment Summarized Financial Information Debt		$ 3,900

[1] 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).

[2] The stated rate for the construction loan is LIBOR + 2.25%. The interest rate spread decreases to 2.00% upon receipt of certificate of occupancy. It is further reduced to 1.75% upon stabilization. To fulfill interest rate protection requirements an interest rate cap was purchased at 4.50%.

[3] The ownership interest in Invesco, L.P. was sold prior to December 31, 2014. The Company purchased the remaining 50% interest in Broadmoor Austin Associates on June 22, 2015. The ownership interest in DRA-N. PA was disposed of on August 12, 2015. The ownership interest in Residence Inn Tower Bridge was sold on December 30, 2015. See below for further detail on 2015 dispositions.