Partners Equity of the Operating Partnership (Details Textuals) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended		12 Months Ended			0 Months Ended	9 Months Ended	36 Months Ended
	Apr. 10, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Sep. 30, 2012 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Dec. 31, 2012 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Oct. 18, 2013 BRANDYWINE OPERATING PARTNERSHIP, L.P.	May 30, 2013 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Jul. 15, 2013 6.90% Series E-linked Preferred Units [Member] BRANDYWINE OPERATING PARTNERSHIP, L.P.	Sep. 30, 2013 6.90% Series E-linked Preferred Units [Member] BRANDYWINE OPERATING PARTNERSHIP, L.P.	Mar. 10, 2013 Offering Program [Member]	Mar. 10, 2013 Offering Program [Member] BRANDYWINE OPERATING PARTNERSHIP, L.P.
Earnings per Common Partnership Unit [Line Items]
Stock Issued During Period, Shares, New Issues	12,650,000
Additional shares granted under option to purchase in public offering	1,650,000
Proceeds from Issuance of Common Stock	$ 181,700	$ 181,527	$ 0		$ 181,527	$ 0
Distribution Declared Per Common Partnership Unit									$ 0.15
Distributions payable		25,579		23,652	25,579		23,652	23,800
Preferred Stock, Dividend Rate, Percentage		6.90%		6.90%	6.90%		6.90%				6.90%
Preferred Stock, Liquidation Preference Per Share											$ 25.00
Dividends, Preferred Stock, Cash		$ 5,175	$ 7,832							$ 1,700
Stock Issued During Period, Shares, Other												6,421,553	6,421,553
Average Sales Price Per Share												$ 12.50