Investment in Unconsolidated Real Estate Ventures (Textual) (Details)																										1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
		Jan. 10, 2018 USD ($) Real_Estate_Investment	Oct. 18, 2017 USD ($) ft² property	Oct. 17, 2017 USD ($) property	Sep. 14, 2017 USD ($) ft² property	Jan. 31, 2017 USD ($) property	Sep. 30, 2016 USD ($) ft² Apartment_unit NumberofCar.	Sep. 22, 2016 USD ($) ft²	Aug. 31, 2016 USD ($)	Aug. 19, 2016 USD ($)	Jun. 30, 2016 USD ($) ft²	Jun. 10, 2016 USD ($)	Mar. 02, 2016 USD ($)	Feb. 04, 2016 USD ($) ft² property	Jan. 29, 2016 USD ($)	Dec. 30, 2015 USD ($)	Jun. 22, 2015 USD ($) ft² a property Building	May 29, 2015 USD ($) a	Jan. 30, 2015 USD ($)	Oct. 21, 2014 USD ($)	Oct. 17, 2014 USD ($) ft² property	Oct. 15, 2014 USD ($)	Jul. 31, 2014 USD ($) ft² property Storey	Oct. 16, 2013 USD ($) ft² property	Jul. 31, 2013 USD ($) ft² a property	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) property	Dec. 31, 2016 USD ($) ft²	Jun. 30, 2016 USD ($) ft²	Sep. 30, 2017 USD ($) ft² property	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($) ft² property		Dec. 31, 2015 USD ($) ft² property Storey		Dec. 31, 2011 USD ($)	Dec. 31, 2017		Dec. 31, 2017 property	Dec. 31, 2017 ft²	Dec. 31, 2017 Real_Estate_Investment	Dec. 31, 2017 a	Dec. 31, 2017 Apartment_unit	Dec. 31, 2014 USD ($)	Oct. 27, 2014 Storey	Apr. 03, 2014 ft² property Storey	Dec. 31, 2013 USD ($)	Jan. 25, 2013 USD ($) a Storey Bed	Jul. 10, 2012 USD ($) ft² property	Dec. 20, 2011 property	Jan. 20, 2011 a
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											$ 194,621,000	$ 281,331,000				$ 194,621,000		$ 281,331,000		$ 241,004,000
Management fees																																28,345,000		26,674,000		18,764,000
Accounts receivable																											17,938,000	12,446,000				17,938,000		12,446,000
Property encumbered at the time of venture sale																											320,107,000					320,107,000
Proceeds from real estate venture sales																																145,416,000		21,022,000		6,100,000
Net gain on Real Estate Venture transactions																																80,526,000		20,000,000		7,229,000
Deconsolidated mortgage loan																																0		(20,582,000)		0
Deconsolidated financing liability																																0		(12,384,000)		0
Capital funded to venture for mortgage debt																																6,638,000		28,610,000		68,549,000
Repayment of mortgage debt																																4,931,000		357,151,000		222,836,000
Number of Properties | property																																									93
Cash proceeds after the payment of share of the debt and closing costs																																145,416,000		21,022,000		6,100,000
Advance received for refinancing																																341,000,000		195,000,000		89,000,000
Cash distribution from unconsolidated real estate ventures																																20,781,000		13,065,000		8,557,000
Proceeds from the sale of properties																																171,860,000		784,331,000		247,228,000
Gain (Loss) on Sale																																31,657,000		116,983,000		20,496,000
Amount funded by corporate funds																																72,523,000		20,406,000		150,472,000
Proceeds from repayment of mortgage notes receivable																																151,000		0		$ 88,000,000
Real estate ventures aggregate indebtedness to third parties																											768,912,000	$ 997,466,000				768,912,000		$ 997,466,000
Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																	1,112,236
Acreage of land | a																	66.0
Number of Property units | property																	7
Equity method investment percentage																	50.00%
Payments to Acquire Land																	$ 143,800,000
Encino Trace - Land [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																				320,000
Number of Properties | property																																				2
Number of floors of a building | Storey																																				4
Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																	50.00%
TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Gross sales price						$ 100,500,000
Proceeds from real estate venture sales						27,200,000
Net gain on Real Estate Venture transactions						$ 14,600,000
Sale of ownership interest percentage						50.00%
Allocated gross sales value of ownership interest, percentage						50.00%
Number of Properties Sold | property						398
Guarantee obligations cancelled						$ 3,200,000
Cash proceeds after the payment of share of the debt and closing costs						27,200,000
TB-BDN Plymouth Apartments [Member] | Pennsylvania [Member]
Schedule Of Equity Method Investments [Line Items]
Construction Loan						54,000,000
Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | property																																																2
Number of floors of a building | Storey																																																3
Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																												5,239,632						5,239,632		2,649,926
Gross sales price																												$ 820,000,000						$ 820,000,000		$ 374,600,000
Number of Properties | property																																									81
Number of Properties Sold | property																																		66		27
Proceeds from the sale of properties																																		$ 769,799,000		$ 340,098,000
Gain (Loss) on Sale																																		116,983,000	[1]	22,002,000	[2],[3]
Office Properties [Member] | Broadmoor Austin Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | Building																	7
Office Properties [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																										587,317
Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees																																6,400,000		6,700,000		4,400,000
Accounts receivable																											900,000	$ 1,400,000				900,000		1,400,000
Real Estate Venture [Member] | Lease Commission Income [Member]
Schedule Of Equity Method Investments [Line Items]
Management fees																																4,500,000		$ 3,800,000		$ 2,100,000
Unconsolidated Real Estate Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											13
Investment in Real Estate Ventures, equity method																											194,600,000					194,600,000
Equity method investment percentage																												0.00%						0.00%		0.00%			0.00%
Equity method investment other than temporary impairment charge	[4]																															4,844,000
Real estate ventures aggregate indebtedness to third parties																											768,912,000					768,912,000
Unconsolidated Real Estate Ventures [Member] | TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Equity in income (loss) of Real Estate Ventures						$ 12,600,000
Unconsolidated Real Estate Ventures [Member] | Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																												20.00%						20.00%		20.00%			20.00%
Unconsolidated Real Estate Ventures [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																												70.00%						70.00%		70.00%			70.00%
Unconsolidated Real Estate Ventures [Member] | Land Under Active Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											1
Acreage of land | a																																												1.3
Unconsolidated Real Estate Ventures [Member] | Seven Real Estate Ventures [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											7
Rentable Square Feet | ft²																																										6,700,000
Unconsolidated Real Estate Ventures [Member] | Three Real Estate Ventures [Member] | Land Held For Development [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures | Real_Estate_Investment																																											3
Acreage of land | a																																												4.4
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower One [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures																																											1		1
Number of Property units																																									345				345
Unconsolidated Real Estate Ventures [Member] | Two Other Real Estate Ventures [Member] | Residential Tower Two [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Unconsolidated Investments in Real Estate Ventures																																											1		1
Number of Property units																																									321				321
BDN - Al Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[5],[6]																										43,560,000	$ 67,809,000				43,560,000		$ 67,809,000
Rentable Square Feet | ft²					874,479
Equity method investment percentage																												50.00%						50.00%		50.00%			50.00%	[5],[6],[7]												50.00%
Number of office properties owned | property					5																									5
Cost of equity method investment																														$ 49,100,000
Equity method investment other than temporary impairment charge																														4,800,000		4,844,000	[4]
Cost of equity method investment after recordation of impairment charge																														$ 44,300,000
Impairment Hold Period																														10 years
Residual Capitalization Rates																														7.50%
Effective interest rate	[5],[6]																																						3.94%
Real estate ventures aggregate indebtedness to third parties	[5],[6]																										93,117,000	$ 131,539,000				93,117,000		$ 131,539,000
BDN - Al Venture [Member] | Current Creek Investments, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																																				50.00%
BDN - Al Venture [Member] | 7101 Wisconsin Property Sale [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²					230,904																									239,904
Equity method investment percentage					50.00%
Gross sales price					$ 105,700,000																									$ 105,700,000
Property encumbered at the time of venture sale					37,400,000
Debt instrument prepayment penalty					800,000
Cash proceeds received from sale of venture					63,600,000
Proceeds from real estate venture sales					31,800,000
Net gain on Real Estate Venture transactions					13,800,000
Cash proceeds after the payment of share of the debt and closing costs					$ 31,800,000
BDN - Al Venture [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method									$ 12,600,000
Deconsolidated net assets									45,600,000
Deconsolidated mortgage loan									20,600,000
Deconsolidated financing liability									$ 12,400,000
Recognizing gain or loss on sale																													$ 0
Capital funded to venture for mortgage debt																										$ 10,300,000
Repayment of mortgage debt																												20,600,000
BDN - Al Venture [Member] | Station Square [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																																			497,896
Equity method investment percentage																																																			50.00%
Cost of equity method investment																																																			$ 120,600,000
Equity method investment other than temporary impairment charge																															$ 5,200,000
Provision for impairment of investment in real estate ventures																															10,400,000
Number of Properties | property																																																			3
BDN - Al Venture [Member] | Remaining Properties in Real Estate Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment other than temporary impairment charge																																0
BDN - Al Venture [Member] | Minimum [Member]
Schedule Of Equity Method Investments [Line Items]
Discount Rates																														7.80%
BDN - Al Venture [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Discount Rates																														8.50%
BDN - Al Venture [Member] | Office Properties [Member] | 3141 Fairview Park Drive [Member]
Schedule Of Equity Method Investments [Line Items]
Number of office properties owned | property																																																				3
PJP V [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage								25.00%
Proceeds from real estate venture sales								$ 3,400,000
Net gain on Real Estate Venture transactions								3,200,000
Cash proceeds after the payment of share of the debt and closing costs								3,400,000
Equity in income (loss) of Real Estate Ventures								$ 200,000
PJP V [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²								73,997
Invesco Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Net gain on Real Estate Venture transactions										$ 7,000,000
Equity in income (loss) of Real Estate Ventures										0
Amount of proceeds, net of closing costs										$ 7,000,000
1000 Chesterbrook [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage											50.00%																		50.00%
Gross sales price											$ 32,100,000																		$ 32,100,000
Proceeds from real estate venture sales											9,800,000
Net gain on Real Estate Venture transactions											3,200,000
Cash proceeds after the payment of share of the debt and closing costs											9,800,000
Debt assumed by buyer											$ 23,200,000
Working capital contribution							$ 200,000																			$ 200,000					$ 200,000
1000 Chesterbrook [Member] | One Real Estate Venture [Member] | Office Properties [Member]
Schedule Of Equity Method Investments [Line Items]
Area of Real Estate Property | ft²											172,286																		172,286
evo at Cira Centre South Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method													$ 28,300,000
Equity method investment percentage													50.00%																																					30.00%
Cost of equity method investment																																																		$ 4,000,000
Construction Loan												$ 97,800,000
Number of floors of a building | Storey																																																		33
Student housing bed capacity | Bed																																																		850
Area of developed parcels of land (in acres) owned by a Real Estate Venture | a																																																		1
Equity Method Investment, Underlying Equity in Net Assets																																																		$ 8,500,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																																																		$ 4,500,000
Cash paid to acquire real estate ventures													$ 12,800,000
Equity method investment percentage of interests acquired by the Company and HSRE													30.00%
Debt instrument maturity date												Jul. 25, 2016
Cash distribution from unconsolidated real estate ventures												$ 6,300,000
Guarantees, maximum exposure amount																											55,400,000					55,400,000
Guarantor obligations, current carrying value																											55,400,000					$ 55,400,000
evo at Cira Centre South Venture [Member] | Secured Debt [Member]
Schedule Of Equity Method Investments [Line Items]
Debt instrument maturity date												Oct. 31, 2019
Term loans												$ 117,000,000
Debt instrument, description of variable rate basis																																LIBOR + 2.25
Debt instrument optional extended maturity date												Jun. 30, 2021
Advance received for refinancing												$ 105,000,000
Additional capacity under the term loan may be funded if certain criterion relating to the operating performance of the student housing tower are met												$ 12,000,000
evo at Cira Centre South Venture [Member] | Secured Debt [Member] | LIBOR [Member]
Schedule Of Equity Method Investments [Line Items]
Debt instrument, basis spread on variable rate												2.25%
evo at Cira Centre South Venture [Member] | Campus Crest Properties, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																																		30.00%
evo at Cira Centre South Venture [Member] | HSRE, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage													50.00%																																					40.00%
Cash paid to acquire real estate ventures													$ 6,600,000
evo at Cira Centre South Venture [Member] | Maximum [Member] | Secured Debt [Member]
Schedule Of Equity Method Investments [Line Items]
Effective interest rate												5.25%
MAP Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[8]																										15,450,000	20,893,000				$ 15,450,000		20,893,000
Equity method investment percentage	[7],[8]																																						50.00%
Real estate ventures aggregate indebtedness to third parties	[8]																										180,800,000	180,800,000				180,800,000		180,800,000
MAP Venture [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²														3,924,783
Equity method investment percentage														50.00%
Gross sales price														$ 398,100,000
Number of Properties Sold | property														58
Percentage of fee interests in land sold														100.00%
Ground lease annual payments																																$ 11,900,000
Ground lease annual rent expense increase percentage																																							2.50%
Reassessment period for change in ground lease annual payments																																10 years
Ground Lease Terms																																Annual payments by the MAP Venture, as tenant under the Ground Leases, initially total $11.9 million and increase 2.5% annually through November 2025.
Non-Recourse Debt														$ 180,800,000
Proceeds from the sale of properties														354,000,000
Ownership percentage value														$ 25,200,000
Coppell Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage															50.00%
Proceeds from real estate venture sales															$ 4,600,000
Cash proceeds after the payment of share of the debt and closing costs															4,600,000
Gain (Loss) on Sale															5,700,000
Coppell Associates [Member] | Other Liabilities [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method															$ 1,100,000
Residence Inn Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																$ 900,000
Equity method investment percentage																50.00%
Proceeds from real estate venture sales																$ 6,100,000
Cash proceeds after the payment of share of the debt and closing costs																6,100,000
Gain (Loss) on Sale																$ 5,200,000
51 N 50 Patterson [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											21,212,000	20,318,000				$ 21,212,000		20,318,000
Equity method investment percentage																		70.00%																					70.00%	[7]
Payments to Acquire Land																		$ 15,200,000
Area owned by real estate venture of undeveloped parcels of land | a																		0.9
Real estate ventures aggregate indebtedness to third parties																											0	0				0		0
51 N 50 Patterson [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																		30.00%
Payments to Acquire Land																		$ 6,500,000
1250 First Street Office [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											17,867,000	17,304,000				17,867,000		17,304,000
Equity method investment percentage																		70.00%																					70.00%	[7]
Payments to Acquire Land																		$ 13,200,000
Area owned by real estate venture of undeveloped parcels of land | a																		0.5
Real estate ventures aggregate indebtedness to third parties																											0	0				0		0
1250 First Street Office [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																		30.00%
Payments to Acquire Land																		$ 5,700,000
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[9],[10]																										22,268,000	27,462,000				$ 22,268,000		27,462,000
Equity method investment percentage																																							50.00%	[7],[9],[10]													50.00%
Number of floors of a building | Storey																																															29
Area of developed parcels of land (in acres) owned by a Real Estate Venture | a																																																					1
Debt instrument, description of variable rate basis																																LIBOR + 1.75
Payments to Acquire Land																																						$ 9,300,000
Remeasurement gain or loss on investments																						$ 0
Square foot of contemporary glass tower development | ft²							455,000
Number of luxury apartments | Apartment_unit							321
Square feet of commercial space | ft²							24,000
Number of Car Structured Parking Facility | NumberofCar.							215
Real estate ventures aggregate indebtedness to third parties	[9],[10]																										88,860,000	79,250,000				$ 88,860,000		79,250,000
Brandywine Nineteen Nineteen Ventures [Member] | LCOR/CalSTRS [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																				50.00%
Aggregate gross sales price of a joint venture																				$ 16,400,000
General Partners' Contributed Capital																				5,200,000
Net gain on sale of undepreciated real estate																				$ 8,200,000
Outstanding construction loan																											88,900,000					88,900,000
Equity method investments, Cash contributions																																29,600,000
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											14,000,000					14,000,000
Rentable Square Feet | ft²			1,164,496																		590,881		232,274																			1,570,123
Equity method investment percentage			50.00%
Gross sales price			$ 333,250,000
Proceeds from real estate venture sales			172,742,000
Net gain on Real Estate Venture transactions			$ 40,092,000																								$ 52,200,000
Number of office properties owned | property																																									11
Number of Properties | property																					7		2
Number of Properties Sold | property			8	7																							8
Cash proceeds after the payment of share of the debt and closing costs			$ 172,742,000
Amount of proceeds, net of closing costs			86,371,000
Equity method investments, Cash contributions																					$ 18,900,000		$ 12,800,000
Equity method investments, Closing costs																					200,000		100,000
Equity method investment, Consideration transferred																							48,200,000
Mortgage loans outstanding																							$ 34,500,000
Mortgage loans interest rate																							3.87%
Equity Method Investments Purchase Adjustments																							$ 900,000
Business acquisition cost of acquired entity transaction costs borne by seller																							600,000
Amount funded by corporate funds																					128,100,000
Short-term Bank Loans and Notes Payable																					$ 88,000,000
Real estate ventures aggregate indebtedness to third parties			150,968,000	$ 151,000,000
Cash proceeds after the payment of mortgage debt, closing costs and prorations			86,400,000
Deferred gain on sale			$ 12,072,000
Austin Joint Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																							50.00%
Area of Real Estate Property | ft²																								1,398,826
Aggregate gross sales price of a joint venture																								$ 330,000,000
Equity method investments, Cash contributions																							$ 6,400,000
Number of properties contributed to a joint venture | property																								7
Equity method investment, agreement to pay future capital expenditures																								$ 5,200,000																									$ 800,000
Equity Method Investment, Additional Distribution Rights																																							10.00%
Austin Joint Venture [Member] | DRA Advisors LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment percentage																																							50.00%
Non-Recourse Debt																								230,600,000
Equity Method Investment, Distribution, Net of Initial Funding Agreement																								266,300,000
Amount Of Participant Contribution																								49,700,000
Equity method investments, Closing costs																								1,900,000
Closing Prorations and Lender Holdbacks																								6,900,000
Proceeds from Equity Method Investment, Dividends or Distributions																								$ 271,500,000
Austin Joint Venture [Member] | Office Properties [Member] | Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																																																192,396
Austin, Texas [Member]
Schedule Of Equity Method Investments [Line Items]
Number of floors of a building | Storey																							3
Austin, Texas [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, agreement to pay future capital expenditures																																														$ 4,400,000
River Place [Member]
Schedule Of Equity Method Investments [Line Items]
Proceeds from repayment of mortgage notes receivable																			$ 88,000,000
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method	[11]																										$ 37,179,000	$ 36,356,000				37,179,000		$ 36,356,000
Equity method investment percentage																												50.00%						50.00%					50.00%	[7],[11]
Capital funded to venture for mortgage debt																																6,700,000
Area owned by real estate venture of undeveloped parcels of land | a																									1.3
Real estate ventures aggregate indebtedness to third parties	[11]																										6,664,000	$ 1,004,000				6,664,000		$ 1,004,000
Additional borrowing fund to tenant improvements and leasing commissions																											150,000,000					150,000,000
Guarantees, maximum exposure amount																											41,300,000					41,300,000
4040 Wilson Venture [Member] | Mixed Use Property [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Properties | property																									8
Area of Real Estate Property | ft²																									427,500
4040 Wilson Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Cash paid to acquire real estate ventures																									$ 36,000,000
Capital contribution to venture																											36,900,000					36,900,000
4040 Wilson Venture [Member] | Ashton Park
Schedule Of Equity Method Investments [Line Items]
Capital contribution to venture																											36,900,000					36,900,000
PJP VII [Member]
Schedule Of Equity Method Investments [Line Items]
Investment in Real Estate Ventures, equity method																											1,156,000	980,000				1,156,000		980,000
Equity method investment percentage	[7]																																						25.00%
Real estate ventures aggregate indebtedness to third parties																											4,792,000	$ 4,956,000				4,792,000		$ 4,956,000
Guarantees, maximum exposure amount																											$ 400,000					$ 400,000
Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Number of Investments in Real Estate Ventures | Real_Estate_Investment		10
Subsequent Event [Member] | Evo at Cira Disposition [Member]
Schedule Of Equity Method Investments [Line Items]
Gross sales price		$ 197,500,000
Proceeds from real estate venture sales		$ 43,000,000
Sale of ownership interest percentage		50.00%
Cash proceeds after the payment of share of the debt and closing costs		$ 43,000,000

[1] Gain/(Loss) on Sale is net of closing and other transaction related costs.

[2] Gain on Sale is net of closing and other transaction related costs.

[3] Total gain on sale does not include a deferred gain of $0.5 million related to a prior sale.

[4] See “Brandywine - AI Venture: Other Than Temporary Impairment” section below.

[5] On October 18, 2017, the DRA (G&I) Austin venture sold eight office properties in Austin, Texas containing 1,164,496 square feet and encumbered by $151.0 million of mortgage debt for a gross sales price of $333.3 million. On September 14, 2017, the BDN-AI Venture completed the sale of 7101 Wisconsin Avenue, an office property containing 239,904 rentable square feet, located in Bethesda, Maryland, for a gross sales price of $105.7 million. On January 31, 2017, the Company sold its 50% interest in TB-BDN Plymouth Apartments, LP. On September 22, 2016, the Company liquidated its 25% ownership interest in PJP V. On June 30, 2016, the Company liquidated its 50% ownership interest in the venture known as 1000 Chesterbrook. The ownership interest in Invesco, L.P. was sold prior to December 31, 2015, and on August 19, 2016, the Company assigned its residual profits interest to the general partner of Invesco. See below for further detail on these dispositions.

[6] See “Brandywine - AI Venture: 7101 Wisconsin Avenue” and “Brandywine - AI Venture: Other Than Temporary Impairment” sections below for information discussing activity that occurred during 2017 relating to this venture.

[7] Ownership percentage represents the Company’s entitlement to residual distributions after payments of priority returns, where applicable.

[8] In order to fulfill interest rate protection requirements, a LIBOR interest rate cap of 1.75% was purchased, effective February 3, 2016 and maturing February 9, 2018, for a notional amount of $200.8 million. There are three options to extend the maturity date of the debt for three successive terms, each year representing a separate option.

[9] The basis differences associated with these ventures are allocated between cost and the underlying equity in the net assets of the investee and is accounted for as if the entity were consolidated (i.e., allocated to the Company’s relative share of assets and liabilities with an adjustment to recognize equity in earnings for the appropriate depreciation/amortization). The Company increased its ownership interest in the HSRE-BDN I, LLC venture (also referred to as the “evo at Cira South Venture”) to 50% on March 2, 2016. On June 10, 2016, HSRE-BDN I, LLC refinanced its debt. See “evo at Cira South Venture” section below for further details on these transactions. Also, see “Austin Venture” section below for information discussing this venture’s sale of eight office properties during 2017. Subsequent to December 31, 2017, the Company disposed of its interest in the evo at Cira South Venture. See Note 20, “Subsequent Events,” to the consolidated financial statements for further information.

[10] The stated rate for the construction loan is LIBOR + 1.75%. To fulfill interest rate protection requirements, an interest rate cap was purchased at 4.50%.

[11] During the fourth quarter of 2017, 4040 Wilson obtained a secured construction loan with a total borrowing capacity of $150.0 million.