Real Estate Investments, Acquisitions and Dispositions (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended
	Dec. 31, 2014 acre	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 acre	Dec. 31, 2013	Dec. 31, 2012	Dec. 19, 2013 sqft Storey	Oct. 17, 2013 sqft	Jun. 14, 2013 sqft	Apr. 07, 2014	Jul. 18, 2012 sqft	Jun. 22, 2012 sqft	Mar. 22, 2012 sqft	Jan. 17, 2012 sqft	Jun. 28, 2013 sqft	Jun. 19, 2013 sqft	Feb. 19, 2014 Properties Storey sqft acre	Apr. 25, 2013 acre	Apr. 03, 2014	Oct. 16, 2013	Nov. 19, 2013 acre	Mar. 27, 2014 acre	Apr. 16, 2014 acre	Aug. 05, 2013 acre	Feb. 25, 2013 sqft Properties	Oct. 17, 2014 sqft Real_Estate_Investments	Jul. 31, 2014 Properties
Significant Acquisitions and Disposals [Line Items]
Provision for impairment on assets held for sale									$ 1,765,000	$ 0	$ 0
Business Acquisition, Pro Forma Revenue										610,979,000	592,753,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual										3,400,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual										200,000
Net gain (loss) on sale of undepreciated real estate									458,000	6,866,000	0
Land	669,635,000				680,513,000				669,635,000	680,513,000
Adjustment to Record Land Acquisition to Fair Value									0	7,752,000	0
Payments to Acquire Real Estate									18,443,000	161,604,000	77,555,000
Gains (Losses) on Sales of Investment Real Estate									4,901,000	0	0
Equity Method Investments	225,004,000				180,512,000				225,004,000	180,512,000	193,555,000
Secured Debt	654,590,000				670,151,000				654,590,000	670,151,000
Balance of the Financing Obligation	37,558,000				32,923,000				37,558,000	32,923,000
Gain (Loss) on Sale of Properties									900,000	3,382,000	34,774,000
Net gain (loss) on sale of undepreciated real estate									1,184,000	(137,000)	0
Area Owned By Real Estate Venture Of Undeveloped Parcels Of Land	3.0								3.0
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax										21,805,000	(60,011,000)
Business Acquisition, Pro Forma Net Income (Loss)										25,957,000	(16,970,000)
Continuing operations (in dollars per share)									$ (0.01)	$ 0.20	$ (0.36)
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax, Per Share, Basic										$ 0.14	$ (0.42)
Income (Loss) from Continuing Operations, Per Diluted Share									$ (0.01)	$ 0.20	$ (0.36)
Business Acquisition, Pro Forma Income (Loss) from Continuing Operations before Changes in Accounting and Extraordinary Items, Net of Tax, Per Share, Diluted										$ 0.14	$ (0.42)
Earnings Per Share, Basic	$ (0.02)	$ 0.04	$ 0.00	$ (0.03)	$ 0.12	$ 0.06	$ 0.03	$ 0.01	$ 0.00	$ 0.23	$ (0.06)
Pro Forma, Earnings Per Share, Basic										$ 0.17	$ (0.12)
Earnings Per Share, Diluted	$ (0.02)	$ 0.04	$ 0.00	$ (0.03)	$ 0.12	$ 0.06	$ 0.03	$ 0.01	$ 0.00	$ 0.23	$ (0.06)
Pro Forma Earnings Per Share, Diluted										$ 0.17	$ (0.12)
Other assets	65,111,000				62,377,000				65,111,000	62,377,000
One and Two Commerce Square [Member]
Significant Acquisitions and Disposals [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment												255,705,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage												99.00%
Net gain (loss) on sale of undepreciated real estate												981,000
Number of floors of a building												41
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds												331,800,000
Business Combination, Assumption of Existing Mortgage Debt												237,100,000
Lease percentage of acquired property					86.70%					86.70%
Net rentable space of property acquired												1,896,142
Acquisition related costs												900,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles												85,036,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other												(8,637,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net												332,104,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt												(238,082,000)
Business Combination, return of capital on equity method investment												(30,424,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other												10,423,000
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value												(946,000)
Business Combination, Total Cash Payment at Settlement												73,075,000
Four Points Centre [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land												22.3
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds												47,300,000
Lease percentage of acquired property												99.20%
Business Acquisition Purchase Price Allocation Intangible Assets												6,500,000
Business Acquisition Purchase Price Allocated To Market Lease Liabilities												1,000,000
Net rentable space of property acquired												192,396
Acquisition related costs												100,000
Business Acquisition Purchase Price Allocation Building												36,000,000
Business Acquisition Purchase Price Allocation, Land Portion												5,800,000
Cira Ground Land Parcel [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land																										0.8
Ground Lease Buy-out, Total Cost																										24,600,000
Accrued Rent																										12,100,000
Acquisition related costs																										1,400,000
Rob Roy - Land [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land																											16.8
Sales price of properties sold																											3,500,000
Net gain (loss) on sale of undepreciated real estate									1,200,000
1000 Atrium Way and Libertyview [Member] [Member]
Significant Acquisitions and Disposals [Line Items]
Number of Real Estate Properties	2								2
Valleybrooke Office Park [Member]
Significant Acquisitions and Disposals [Line Items]
Disposal group, number of properties held for sale	5								5
Net rentable square feet of properties sold	279,934								279,934
Sales price of properties sold	37,900,000								37,900,000
Campus Pointe [Member]
Significant Acquisitions and Disposals [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal									4,700,000
Net rentable square feet of properties sold		172,943
Sales price of properties sold		42,500,000
West Point II Land [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land																												5.3
Sales price of properties sold																												1,600,000
1000 Atrium Way [Member]
Significant Acquisitions and Disposals [Line Items]
Net rentable space of property acquired	99,668								99,668
875 First Avenue [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties												100,000
Net rentable square feet of properties sold												50,000
Sales price of properties sold												3,800,000
1336 Enterprise Drive [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties													200,000
Net rentable square feet of properties sold													39,330
Sales price of properties sold													2,600,000
Dabney Land, East [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land																													8
Sales price of properties sold																													500,000
Net gain (loss) on sale of undepreciated real estate										(100,000)
Pacific View Plaza [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties														(500,000)
Net rentable square feet of properties sold														51,695
Sales price of properties sold														10,300,000
Princeton Pike Corporate Center [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties										5,300,000					900,000
Number of flex/office properties sold																														8
Net rentable square feet of properties sold																														800,546
Sales price of properties sold																														121,000,000
Oaklands Corporate Center [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																9,900,000
Number of flex/office properties sold																11
Net rentable square feet of properties sold																466,719
Sales price of properties sold																52,700,000
Pacific Ridge Corporate Center [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																	(2,800,000)
Net rentable square feet of properties sold																	121,381
Sales price of properties sold																	29,000,000
South Lake at Dulles Corner [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																		14,500,000
Net rentable square feet of properties sold																		268,240
Sales price of properties sold																		91,100,000
304 Harper Drive [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																			200,000
Net rentable square feet of properties sold																			32,978
Sales price of properties sold																			3,000,000
The Bluffs [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																				(900,000)
Net rentable square feet of properties sold																				68,708
Sales price of properties sold																				18,000,000
100 Arrandale Boulevard [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																				(400,000)
Net rentable square feet of properties sold																				34,931
Sales price of properties sold																				3,500,000
1700 Paoli Pike [Member]
Significant Acquisitions and Disposals [Line Items]
Gain (Loss) on Sale of Properties																					(400,000)
Net rentable square feet of properties sold																					28,000
Sales price of properties sold																					2,700,000
Four Points Centre [Member]
Significant Acquisitions and Disposals [Line Items]
Number of floors of a building												3												3
Net rentable space of property acquired																								192,396
Number of Real Estate Properties																								2
Libertyview [Member]
Significant Acquisitions and Disposals [Line Items]
Net rentable space of property acquired	121,737								121,737
Austin Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Equity Method Investments	40,374,000								40,374,000
Company's Ownership Percentage in the Real Estate Venture	50.00%								50.00%
Net rentable space of property acquired																															590,881
Number of Real Estate Properties																															7	2
Austin Joint Venture [Member] | Four Points Centre [Member]
Significant Acquisitions and Disposals [Line Items]
Non-Recourse Debt																								29,000,000
Brandywine - Al Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Equity Method Investments	45,712,000								45,712,000
Company's Ownership Percentage in the Real Estate Venture	50.00%								50.00%
Encino Trace - Land [Member]
Significant Acquisitions and Disposals [Line Items]
Number of potential development properties																						2
Number of floors of a building																						4
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds																						14,000,000
Total potential development capacity																						320,000
Land			4,600,000
Escrow Deposit																						1,000,000
Construction in Progress, Gross																						8,400,000
Lease percentage of acquired property																						75.00%
Area Owned by Company of Undeveloped Parcels Of Land																						54.1
Three Logan Square [Member]
Significant Acquisitions and Disposals [Line Items]
Area of Land																							1.8
Ground Lease Buy-out, Total Cost																							20,800,000
Adjustment to Record Land Acquisition to Fair Value																							4,300,000
Acquisition related costs																							100,000
Secured Debt [Member]
Significant Acquisitions and Disposals [Line Items]
Long-term Debt, Gross	655,934,000				669,762,000				655,934,000	669,762,000
Secured Debt	654,590,000				670,151,000				654,590,000	670,151,000
Secured Debt [Member] | Two Commerce Square [Member]
Significant Acquisitions and Disposals [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate												3.96%
Long-term Debt, Fair Value												107,900,000
Long-term Debt, Gross												112,000,000
Secured Debt [Member] | One Commerce Square [Member]
Significant Acquisitions and Disposals [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate												5.67%
Long-term Debt, Fair Value												130,200,000
Long-term Debt, Gross												125,100,000
Subsidiaries [Member]
Significant Acquisitions and Disposals [Line Items]
Provision for impairment on assets held for sale									1,765,000	0	0
Net gain (loss) on sale of undepreciated real estate									458,000	6,866,000	0
Adjustment to Record Land Acquisition to Fair Value									0	7,752,000
Payments to Acquire Real Estate									18,443,000	161,604,000	77,555,000
Gains (Losses) on Sales of Investment Real Estate									4,901,000	0	0
Equity Method Investments	225,004,000				180,512,000				225,004,000	180,512,000
Secured Debt	654,590,000				670,151,000				654,590,000	670,151,000
Balance of the Financing Obligation	37,558,000				32,923,000				37,558,000	32,923,000
Gain (Loss) on Sale of Properties									900,000	3,382,000	34,774,000
Net gain (loss) on real estate venture transactions									(417,000)	3,683,000	0
Net gain (loss) on sale of undepreciated real estate									1,184,000	(137,000)	0
Continuing operations (in dollars per share)									$ (0.01)	$ 0.20	$ (0.36)
Income (Loss) from Continuing Operations, Per Diluted Share									$ (0.01)	$ 0.20	$ (0.36)
Earnings Per Share, Basic									$ 0.00	$ 0.23	$ (0.06)
Earnings Per Share, Diluted									$ 0.00	$ 0.23	$ (0.06)
Other assets	65,111,000				62,377,000				65,111,000	62,377,000
Brandywine Realty Trust [Member] | Austin Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Company's Ownership Percentage in the Real Estate Venture	50.00%								50.00%
Aggregate gross sales price of a joint venture																									330,000,000
Brandywine Realty Trust [Member] | Austin Joint Venture [Member] | Four Points Centre [Member]
Significant Acquisitions and Disposals [Line Items]
Aggregate gross sales price of a joint venture																								41,500,000
Amount Of Participant Contribution																								5,900,000
Net gain (loss) on real estate venture transactions									(200,000)
Proceeds from Equity Method Investment, Dividends or Distributions																								34,400,000
DRA Advisors LLC [Member] | Austin Joint Venture [Member]
Significant Acquisitions and Disposals [Line Items]
Company's Ownership Percentage in the Real Estate Venture	50.00%								50.00%
Non-Recourse Debt																									230,600,000
Amount Of Participant Contribution																									49,700,000
Proceeds from Equity Method Investment, Dividends or Distributions																									271,500,000
DRA Advisors LLC [Member] | Austin Joint Venture [Member] | Four Points Centre [Member]
Significant Acquisitions and Disposals [Line Items]
Amount Of Participant Contribution																								5,900,000
Encino Trace - Building I [Member]
Significant Acquisitions and Disposals [Line Items]
Construction in Progress, Gross	38,800,000								38,800,000
Valleybrooke Office Park [Member]
Significant Acquisitions and Disposals [Line Items]
Provision for impairment on assets held for sale									1,765,000
Gains (Losses) on Sales of Investment Real Estate									$ 200,000