Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended				3 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 02, 2010	Dec. 31, 2012 Restatement Adjustment [Member]	Sep. 30, 2012 Restatement Adjustment [Member]	Jun. 30, 2012 Restatement Adjustment [Member]	Dec. 31, 2011 Restatement Adjustment [Member]	Dec. 31, 2013 The Grove at Cira Centre South [Member]	Dec. 31, 2013 PJP VII [Member]	Dec. 31, 2013 Subsidiaries [Member]	Dec. 31, 2013 TB-BDN Plymouth Apartments [Member]
Summary of Significant Accounting Policies [Line Items]
Tax Basis of Assets, Cost for Income Tax Purposes											$ 4,000,000,000
Summary Of Significant Accounting Policies (Textuals) [Abstract]
Guarantor Obligations, Current Carrying Value									24,700,000	500,000		3,200,000
Revenue increased by straight-line rent adjustment	17,700,000	21,100,000	17,900,000
Increased revenue due to amortization of deferred rent	2,400,000		2,400,000
Decrease in revenue due to amortization of lease incentives	700,000	800,000	1,600,000
Increase in shares due to amendments in plan, shares solely available for options and share appreciation rights	2,983,569			3,600,000
Increase in Common shares available for future awards				6,000,000
Common shares available for future awards	5,195,177
Options awarded, term	one to ten-year
Award vesting term, minimum	1 year
Award vesting term, maximum	10 years
Stock-based compensation expense	8,300,000	8,600,000	6,400,000
Stock-based compensation expense, capitalized	1,400,000	2,600,000	1,500,000
Out of period stock compensation expense adjustment					600,000
Overstatement (Understatement) of Expense due to Out of Period Adjustment					$ 600,000	$ (200,000)	$ (300,000)	$ (100,000)
Treasury Stock, Shares		0