Summary of Significant Accounting Policies (Textual) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 USD ($) Customer	Dec. 31, 2014 USD ($) Customer	Jan. 31, 2017 USD ($)	Jun. 10, 2016 USD ($)	Jun. 02, 2010 shares
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties	$ 997,466,000	$ 794,571,000
Revenue increased by straight-line rent adjustment	26,300,000	21,600,000	$ 13,700,000
Increased revenue due to amortization of deferred rent	2,100,000	2,000,000	2,400,000
Decrease in revenue due to amortization of lease incentives	2,000,000	1,800,000	1,500,000
Share-based compensation expense	5,600,000	7,300,000	6,100,000
Share-based compensation expense, capitalized	1,000,000	1,900,000	$ 1,700,000
Variable interest entity, assets	417,100,000	422,900,000
Variable interest entity, liabilities	$ 254,600,000	$ 258,200,000
Common shares available for future awards | shares	4,295,559
Increase in Common shares available for future awards | shares						6,000,000
Employee Stock Option And Share Appreciation Rights
Summary Of Significant Accounting Policies (Textual) [Abstract]
Common shares available for future awards | shares	2,377,778					3,600,000
Customer Concentration Risk [Member] | Rental Revenue [Member]
Summary Of Significant Accounting Policies (Textual) [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 (Textual) [Abstract]
Property, Plant and Equipment, Useful Life	55 years
Tenant Improvements Useful Lives	16 years
Minimum [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Property, Plant and Equipment, Useful Life	5 years
Tenant Improvements Useful Lives	1 year
TB-BDN Plymouth Apartments [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Guarantees, maximum exposure amount	$ 3,200,000
Construction Loan	56,000,000
TB-BDN Plymouth Apartments [Member] | Subsequent Event [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Sale of ownership interest percentage				50.00%
Guarantee obligations cancelled				$ 3,200,000
1919 Venture [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Guarantees, maximum exposure amount	88,900,000
Unconsolidated Real Estate Ventures [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties	997,466,000
Capitalized interest	1,900,000	$ 2,000,000	$ 2,000,000
evo at Cira Centre South Venture [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Guarantor obligations, current carrying value	52,500,000
Construction Loan					$ 97,800,000
PJP VII [Member]
Summary Of Significant Accounting Policies (Textual) [Abstract]
Real estate ventures aggregate indebtedness to third parties	4,956,000	$ 5,621,000
Guarantees, maximum exposure amount	$ 400,000