Summary of Significant Accounting Policies (Textual) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) Customer shares	Dec. 31, 2014 USD ($) Customer	Dec. 31, 2013 USD ($) Customer	Jun. 02, 2010 shares
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Revenue increased by straight-line rent adjustment	$ 21,600,000	$ 13,700,000	$ 17,700,000
Increased revenue due to amortization of deferred rent	2,000,000	2,400,000	2,400,000
Decrease in revenue due to amortization of lease incentives	$ 1,800,000	1,500,000	700,000
Common shares available for future awards | shares	4,295,559
Increase in Common shares available for future awards | shares				6,000,000
Stock-based compensation expense	$ 7,300,000	6,100,000	8,300,000
Stock-based compensation expense, capitalized	1,900,000	1,700,000	1,400,000
Variable interest entity, assets	422,900,000
Variable interest entity, liabilities	$ 258,200,000
Employee Stock Option And Share Appreciation Rights
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Common shares available for future awards | shares	2,624,067			3,600,000
Options [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Stock-based compensation expense	$ 0	0	700,000
Stock-based compensation expense, capitalized	$ 0	$ 0	$ 100,000
Customer Concentration Risk [Member] | Rental Revenue [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Number of tenant accounted for 10% or more of the Company’s rents | Customer	0	0	0
Maximum [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life	55 years
Tenant Improvements Useful Lives	16 years
Maximum [Member] | Options [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Share based compensation, term	10 years
Minimum [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life	5 years
Tenant Improvements Useful Lives	1 year
Minimum [Member] | Options [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Share based compensation, term	1 year
The Grove at Cira Centre South [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Guarantor obligations, current carrying value	$ 24,700,000
TB-BDN Plymouth Apartments [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Guarantor obligations, current carrying value	3,200,000
PJP VII [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Guarantor obligations, current carrying value	500,000
Unconsolidated Real Estate Ventures [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Capitalized interest	2,000,000	$ 2,000,000	$ 600,000
1919 Venture [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Guarantor obligations, current carrying value	$ 88,900,000
New Accounting Pronouncement, Early Adoption Effect [Member]
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Deferred financing costs reclassified from the deferred costs line and netted against the debt liability		$ 24,000,000