Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Reportable_Segments		Dec. 31, 2013		Dec. 31, 2012	Oct. 17, 2014 sqft Real_Estate_Investments	Jul. 31, 2014 Properties	Apr. 03, 2014	Dec. 19, 2013 Storey
Segment Reporting Information [Line Items]
Number of Reportable Segments											7
Real estate investments, at cost:
Operating properties	$ 4,603,692					$ 4,669,289					$ 4,603,692		$ 4,669,289		$ 4,726,169
Real Estate Held-for-sale	27,436	[1]				0	[1]				27,436	[1]	0	[1]	0
Real Estate Investment Property, at Cost, Gross of Held For Sale	4,631,128					4,669,289					4,631,128		4,669,289		4,726,169
Construction-in-progress	201,360					74,174					201,360		74,174
Land inventory	90,603					93,351					90,603		93,351
Total revenue	147,810		146,558	150,500	152,114	138,658		143,354	140,664	139,554	596,982		562,210		535,679
Property operating expenses, real estate taxes and third party management expenses											(235,965)		(221,769)		(210,848)
Net operating income											361,017		340,441		324,831
Equity Method Investments	225,004					180,512					225,004		180,512		193,555
Equity in income (loss) of real estate ventures											(790)		3,664		2,741
Pennsylvania Suburbs [Member]
Real estate investments, at cost:
Operating properties	1,178,470					1,199,105					1,178,470		1,199,105		1,178,730
Total revenue											160,630		153,426		150,075
Property operating expenses, real estate taxes and third party management expenses											(55,062)		(54,506)		(52,657)
Net operating income											105,568		98,920		97,418
Equity Method Investments	17,385					17,272					17,385		17,272		33,160
Equity in income (loss) of real estate ventures											(777)		925		520
Philadelphia CBD [Member]
Real estate investments, at cost:
Operating properties	1,338,655					1,300,666					1,338,655		1,300,666		988,590
Total revenue											201,809		146,081		131,592
Property operating expenses, real estate taxes and third party management expenses											(75,262)		(55,702)		(50,787)
Net operating income											126,547		90,379		80,805
Equity Method Investments	27,137					19,975					27,137		19,975		27,859
Equity in income (loss) of real estate ventures											46		1,547		1,113
Metropolitan, D.C. [Member]
Real estate investments, at cost:
Operating properties	1,183,652					1,214,965					1,183,652		1,214,965		1,193,200
Total revenue											113,834		116,048		107,656
Property operating expenses, real estate taxes and third party management expenses											(43,399)		(42,641)		(41,485)
Net operating income											70,435		73,407		66,171
Equity Method Investments	73,127					59,905					73,127		59,905		49,169
Equity in income (loss) of real estate ventures											(317)		130		(648)
New Jersey/ Delaware [Member]
Real estate investments, at cost:
Operating properties	392,581					414,716					392,581		414,716		546,644
Total revenue											60,403		60,262		59,671
Property operating expenses, real estate taxes and third party management expenses											(31,650)		(29,981)		(28,506)
Net operating income											28,753		30,281		31,165
Equity Method Investments	0					0					0		0		17,294
Equity in income (loss) of real estate ventures											989		1,245		1,803
Richmond, Virginia [Member]
Real estate investments, at cost:
Operating properties	317,076					310,397					317,076		310,397		309,923
Total revenue											34,180		35,058		35,701
Property operating expenses, real estate taxes and third party management expenses											(15,399)		(14,916)		(14,484)
Net operating income											18,781		20,142		21,217
Equity Method Investments	1,574					1,400					1,574		1,400		1,245
Equity in income (loss) of real estate ventures											349		381		269
CALIFORNIA
Real estate investments, at cost:
Operating properties	193,258					192,584					193,258		192,584		223,736
Total revenue											19,388		18,369		17,463
Property operating expenses, real estate taxes and third party management expenses											(10,165)		(9,411)		(9,043)
Net operating income											9,223		8,958		8,420
Austin, Texas [Member]
Real estate investments, at cost:
Operating properties	0					36,856					0		36,856		285,346
Total revenue											5,610		31,451		32,379
Property operating expenses, real estate taxes and third party management expenses											(3,223)		(13,298)		(13,951)
Net operating income											2,387		18,153		18,428
Equity Method Investments	105,781					81,960					105,781		81,960		64,828
Equity in income (loss) of real estate ventures											(1,080)		(564)		(316)
Corporate [Member]
Real estate investments, at cost:
Construction-in-progress	201,360					74,174					201,360		74,174		48,950
Land inventory	90,603					93,351					90,603		93,351		102,439
Total revenue											1,128		1,515		1,142
Property operating expenses, real estate taxes and third party management expenses											(1,805)		(1,314)		65
Net operating income											(677)		201		1,207
Operating Segments [Member]
Real estate investments, at cost:
Operating properties	4,603,692					4,669,289					4,603,692		4,669,289		4,726,169
Assets Held-for-sale [Member]
Real estate investments, at cost:
Real Estate Held-for-sale	27,436					0					27,436		0		0
BRANDYWINE OPERATING PARTNERSHIP, L.P.
Real estate investments, at cost:
Operating properties	4,603,692					4,669,289					4,603,692		4,669,289
Construction-in-progress	201,360					74,174					201,360		74,174
Land inventory	90,603					93,351					90,603		93,351
Total revenue											596,982		562,210		535,679
Equity Method Investments	225,004					180,512					225,004		180,512
Equity in income (loss) of real estate ventures											(790)		3,664		2,741
Austin Joint Venture [Member]
Segment Reporting Information [Line Items]
Net Rentable Space																590,881
Number of Real Estate Properties																7	2
Real estate investments, at cost:
Equity Method Investments	40,374										40,374
Equity in income (loss) of real estate ventures											$ (574)
Durham, NC [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties	0										0
Four Points Centre [Member]
Segment Reporting Information [Line Items]
Number of floors of a building																		3	3
Net Rentable Space																		192,396
Number of Real Estate Properties																		2
1000 Atrium Way and Libertyview [Member] [Member]
Segment Reporting Information [Line Items]
Number of Real Estate Properties	2										2

[1] (a)Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation or other assets on the balance sheets of the properties held for sale.