Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013 Reportable_Segments	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Pennsylvania Suburbs [Member]	Dec. 31, 2012 Pennsylvania Suburbs [Member]	Dec. 31, 2011 Pennsylvania Suburbs [Member]	Dec. 31, 2013 Philadelphia CBD [Member]	Dec. 31, 2012 Philadelphia CBD [Member]	Dec. 31, 2011 Philadelphia CBD [Member]	Dec. 31, 2013 Metropolitan, D.C. [Member]	Dec. 31, 2012 Metropolitan, D.C. [Member]	Dec. 31, 2011 Metropolitan, D.C. [Member]	Dec. 31, 2013 New Jersey/ Delaware [Member]	Dec. 31, 2012 New Jersey/ Delaware [Member]	Dec. 31, 2011 New Jersey/ Delaware [Member]	Dec. 31, 2013 Richmond, Virginia [Member]	Dec. 31, 2012 Richmond, Virginia [Member]	Dec. 31, 2011 Richmond, Virginia [Member]	Dec. 31, 2013 Austin, Texas [Member]	Dec. 31, 2012 Austin, Texas [Member]	Dec. 31, 2011 Austin, Texas [Member]	Dec. 31, 2013 California [Member]	Dec. 31, 2012 California [Member]	Dec. 31, 2011 California [Member]	Dec. 31, 2013 Corporate [Member]	Dec. 31, 2012 Corporate [Member]	Dec. 31, 2011 Corporate [Member]	Dec. 31, 2013 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Dec. 31, 2012 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Dec. 31, 2011 BRANDYWINE OPERATING PARTNERSHIP, L.P.	Dec. 31, 2013 Austin Joint Venture [Member]	Oct. 16, 2013 Brandywine Realty Trust [Member] Austin Joint Venture [Member] Properties
Segment Reporting Information [Line Items]
Equity Method Investment, Ownership Percentage																																							50.00%	50.00%
Number of reportable segments									7
Real estate investments, at cost:
Operating properties	$ 4,669,289				$ 4,726,169				$ 4,669,289	$ 4,726,169	$ 4,793,080	$ 1,199,105	$ 1,178,730	$ 1,218,071	$ 1,300,666	$ 988,590	$ 953,870	$ 1,214,965	$ 1,193,200	$ 1,255,803	$ 414,716	$ 546,644	$ 545,657	$ 310,397	$ 309,923	$ 307,698	$ 36,856	$ 285,346	$ 257,694	$ 192,584	$ 223,736	$ 254,287	$ 0	$ 0	$ 0	$ 4,669,289	$ 4,726,169
Construction-in-progress	74,174				48,950				74,174	48,950	25,083																						74,174	48,950	25,083	74,174	48,950
Land inventory	93,351				102,439				93,351	102,439	109,008																						93,351	102,439	109,008	93,351	102,439
Total revenue	138,658	143,354	140,644	139,554	136,395	134,238	131,530	133,516	562,210	535,679	538,568	153,426	150,075	148,887	146,081	131,592	125,366	116,048	107,656	119,255	60,262	59,671	58,960	35,058	35,701	36,789	31,451	32,379	30,894	18,369	17,463	16,692	1,515	1,142	1,725	562,210	535,679	538,568
Property operating expenses, real estate taxes and third party management expenses									221,769	210,848	216,791	54,506	52,657	54,734	55,702	50,787	48,831	42,641	41,485	45,135	29,981	28,506	30,564	14,916	14,484	14,739	13,298	13,951	13,034	9,411	9,043	9,407	1,314	(65)	347
Net operating income									340,441	324,831	321,777	98,920	97,418	94,153	90,379	80,805	76,535	73,407	66,171	74,120	30,281	31,165	28,396	20,142	21,217	22,050	18,153	18,428	17,860	8,958	8,420	7,285	201	1,207	1,378
Equity Method Investments	180,512				193,555				180,512	193,555	115,807	17,272	33,160	5,264	19,975	27,859	13,397	59,905	49,169	24,671	0	17,294	6,168	1,400	1,245	1,163	81,960	64,828	65,144	0	0	0	0	0	0	180,512	193,555		17,262
Equity in income of real estate ventures									$ 3,664	$ 2,741	$ 3,775	$ 925	$ 520	$ 1,861	$ 1,547	$ 1,113	$ 466	$ 130	$ (648)	$ (277)	$ 1,245	$ 1,803	$ 1,157	$ 381	$ 269	$ 510	$ (564)	$ (316)	$ 58	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 3,664	$ 2,741	$ 3,775	$ (434)
Number of properties contributed to a joint venture																																								7