Investment in Unconsolidated Ventures (Textual) (Details) $ in Thousands													12 Months Ended
		Dec. 30, 2015 USD ($)	May. 29, 2015 USD ($) a	Jan. 30, 2015 USD ($)	Oct. 21, 2014 USD ($)	Oct. 17, 2014 USD ($) ft² property	Jul. 31, 2014 USD ($) ft² property Storey	Apr. 03, 2014 USD ($) ft² property Storey	Feb. 19, 2014 USD ($) ft² Floor	Oct. 16, 2013 USD ($) ft² property	Jul. 31, 2013 USD ($) ft² a	Jun. 19, 2013 USD ($)	Dec. 31, 2015 USD ($) ft² a property Storey Real_Estate_Ventures Building Apartment_unit		Dec. 31, 2014 USD ($) ft² property		Dec. 31, 2013 USD ($) ft² property Storey	Dec. 31, 2011 USD ($)	Jun. 22, 2015	Mar. 26, 2013 USD ($)	Jan. 25, 2013 USD ($) a Storey Bed	Jan. 20, 2011 a	Dec. 19, 2007 ft² property
Schedule Of Equity Method Investments [Line Items]
Number of unconsolidated investments in Real Estate Ventures | Real_Estate_Ventures													16
Equity Method Investments including net liabilities													$ 239,874		$ 223,790
Company's share of equity (Company's basis)													$ 241,004		225,004		$ 180,512
Number of negative investment real estate ventures | Real_Estate_Ventures													1
Rentable Square Feet | ft²													4,300,000
Number of real estate ventures that owns undeveloped land | Real_Estate_Ventures													2
Area owned by real estate venture of undeveloped parcels of land | a													4.3
Number of real estate ventures that owns land under development | Real_Estate_Ventures													3
Area owned by real estate venture in parcels of land under development | a													2.2
Number of real estate Investments in residential towers | Real_Estate_Ventures													1
Number of apartment units in a real estate Venture | Apartment_unit													345
Number of real estate investments in apartment complex | Real_Estate_Ventures													1
Number of apartment complex in a real estate Venture | Apartment_unit													398
Minimum percentage of unconsolidated equity method investment ownership													20.00%
Maximum percentage of unconsolidated equity method investment ownership													70.00%
Ownership percentage	[1]												0.00%
Proceeds from Equity Method Investment, Dividends or Distributions													$ 6,100		0		16,963
Carrying value of assets													$ 422,900
Number of Properties | property													179
Net gain on sale of undepreciated real estate													$ 0		8,212		0
Acquisition of properties													150,472		18,443		161,604
Proceeds from repayment of mortgage notes receivable													88,000		7,026		200
Payments to Acquire Equity Method Investments													68,549		46,098		33,069
Net gain from remeasurement of investments in real estate ventures													758		458		6,866
Net gain on real estate venture transactions													7,418		$ (417)		$ 3,683
TB-BDN Plymouth Apartments [Member]
Schedule Of Equity Method Investments [Line Items]
Guarantor obligations, current carrying value													3,200
1919 Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Guarantor obligations, current carrying value													$ 88,900
Encino Trace - Land [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²									320,000				320,000
Payments to Acquire Land									$ 14,000
Number of Properties | property													2
Number of floors of a building									4				4
Office Building [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²													2,649,926		645,273		2,472,036
Number of Properties | property													27		8		21
Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²																	192,396
Number of Properties | property								2									2
Number of floors of a building | Storey								3									3
Four Points Centre [Member] | Office Building [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²															192,396
Number of Properties | property															2
Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage																			50.00%
Coppell Associates [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)	[2]												$ 1,130		$ 1,214
Ownership percentage	[1],[2]												50.00%
Real Estate Ventures Owned Office Buildings [Member]
Schedule Of Equity Method Investments [Line Items]
Number of real estate ventures that owns buildings | Real_Estate_Ventures													9
Number of office buildings in Real Estate Ventures | Building													31
Residence Inn Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)		$ 900											$ 0	[3]	723	[3]
Ownership percentage		50.00%											0.00%	[1],[3]
Proceeds from Equity Method Investment, Dividends or Distributions		$ 6,100
Gain on sale of its interest in the real estate venture		$ 5,200
51 N 50 Patterson [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)													$ 16,725		0
Area owned by real estate venture of undeveloped parcels of land | a			0.9
Ownership percentage			70.00%										70.00%	[1]
Payments to Acquire Land			$ 15,200
51 N 50 Patterson [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage			30.00%
Payments to Acquire Land			$ 6,500
1250 First Street Office [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)													$ 14,312		0
Area owned by real estate venture of undeveloped parcels of land | a			0.5
Ownership percentage			70.00%										70.00%	[1]
Payments to Acquire Land			$ 13,200
1250 First Street Office [Member] | JBG [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage			30.00%
Payments to Acquire Land			$ 5,700
25 M Street [Member]
Schedule Of Equity Method Investments [Line Items]
Carrying value of assets													$ 20,500
GI Interchange Office LLC (DRA — N. PA) [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)	[3]												$ 0		0
Rentable Square Feet | ft²																							1,611,961
Ownership percentage	[1],[3]												0.00%
Number of Properties | property																							29
GI Interchange Office LLC (DRA — N. PA) [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage																							20.00%
Brandywine Nineteen Nineteen Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)	[4],[5]												$ 29,086		12,823
Area owned by real estate venture of undeveloped parcels of land | a																						1
Ownership percentage													50.00%	[1],[4],[5]								50.00%
Payments to Acquire Land																		$ 9,300
Brandywine Nineteen Nineteen Ventures [Member] | LCOR/Calstrs [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage					50.00%
Aggregate gross sales price of a joint venture					$ 16,400
General Partners' Contributed Capital					5,200
Net gain on sale of undepreciated real estate					$ 8,200
Outstanding construction loan													$ 19,400
Equity method investments, Cash contributions													29,600
Austin Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)	[4]												$ 60,427		40,374
Rentable Square Feet | ft²						590,881	232,274
Ownership percentage	[1],[4]												50.00%
Number of Properties | property						7	2
Equity method investments, Cash contributions						$ 18,900	$ 12,800
Equity method investments, Closing costs						200	100
Equity method investment, Consideration transferred							48,200
Mortgage loans outstanding							$ 34,500
Mortgage loans interest rate							3.87%
Equity Method Investments Purchase Adjustments							$ 900
Business acquisition cost of acquired entity transaction costs borne by seller							600
Acquisition of properties						128,100
Short-term Bank Loans and Notes Payable						$ 88,000
Austin Joint Venture [Member] | Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Non-Recourse Debt								$ 29,000
Austin Joint Venture [Member] | Four Points Centre [Member] | Office Building [Member]
Schedule Of Equity Method Investments [Line Items]
Rentable Square Feet | ft²								192,396
Austin Joint Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage													50.00%
Aggregate gross sales price of a joint venture										$ 330,000
Equity method investments, Cash contributions							$ 6,400
Number of properties contributed to a joint venture | property										7
Area of Real Estate Property | ft²										1,398,826
Equity method investment, agreement to pay future capital expenditures										$ 5,200							$ 800
Equity Method Investment, Additional Distribution Rights													10.00%
Net gain (loss) on real estate venture transactions																	25,900
Austin Joint Venture [Member] | Brandywine Realty Trust [Member] | Four Points Centre [Member]
Schedule Of Equity Method Investments [Line Items]
Aggregate gross sales price of a joint venture								$ 41,500
Amount Of Participant Contribution								5,900
Proceeds from Equity Method Investment, Dividends or Distributions								$ 34,400
Austin Joint Venture [Member] | DRA Advisors LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage													50.00%
Equity Method Investment, Distribution, Net of Initial Funding Agreement										266,300
Amount Of Participant Contribution										49,700
Equity method investments, Closing costs										1,900
Closing Prorations and Lender Holdbacks										6,900
Proceeds from Equity Method Investment, Dividends or Distributions										271,500
Non-Recourse Debt										$ 230,600
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
River Place [Member]
Schedule Of Equity Method Investments [Line Items]
Proceeds from repayment of mortgage notes receivable				$ 88,000
4040 Wilson Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)													$ 36,626		27,415
Area owned by real estate venture of undeveloped parcels of land | a											1.3
Ownership percentage	[1]												50.00%
Area of Real Estate Property | ft²											426,900
Equity Method Investment, Budgeted Total Project Cost											$ 194,600
Payments to Acquire Equity Method Investments											72,000
4040 Wilson Venture [Member] | Brandywine Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Payments to Acquire Interest in Joint Venture											36,000		$ 35,600
4040 Wilson Venture [Member] | Ashton Park [Member]
Schedule Of Equity Method Investments [Line Items]
Fair value of land, net of amount encumbered											$ 36,000
Six Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Net gain from remeasurement of investments in real estate ventures																	7,800
Fair Value of Contingent Consideration												$ 24,500
Business Acquisition Purchase Price Allocation Building												14,800
Business Acquisition Purchase Price Allocation Land Portion												6,900
Business Acquisition Purchase Price Allocation Intangible Assets												3,300
Business Acquisition Purchase Price Allocated To Market Lease Liabilities												500
Two Tower Bridge [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)												(100)
Investments, Fair Value Disclosure												$ 3,600
Net gain on real estate venture transactions																	$ 3,700
The Grove at Cira Centre South [Member]
Schedule Of Equity Method Investments [Line Items]
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
Guarantor obligations, current carrying value													24,700
Equity Method Investment, Aggregate Cost																					4,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity																					$ 4,500
The Grove at Cira Centre South [Member] | Campus Crest Properties, LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage																					30.00%
The Grove at Cira Centre South [Member] | HSRE, LLC [Member] [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership percentage																					40.00%
BDN Beacon Venture LLC [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)																				$ 17,000
Ownership percentage																				20.00%
PJP VII [Member]
Schedule Of Equity Method Investments [Line Items]
Company's share of equity (Company's basis)													$ 872		$ 911
Ownership percentage	[1]												25.00%
Guarantor obligations, current carrying value													$ 500

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

[2] Carrying amount represents the negative investment balance of the venture and is included in other liabilities.

[3] The ownership interest in Invesco, L.P. was sold prior to December 31, 2014. The Company purchased the remaining 50% interest in Broadmoor Austin Associates on June 22, 2015. The ownership interest in DRA-N. PA was disposed of on August 12, 2015. The ownership interest in Residence Inn Tower Bridge was sold on December 30, 2015. See below for further detail on 2015 dispositions.

[4] 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).

[5] The stated rate for the construction loan is LIBOR + 2.25%. The interest rate spread decreases to 2.00% upon receipt of certificate of occupancy. It is further reduced to 1.75% upon stabilization. To fulfill interest rate protection requirements an interest rate cap was purchased at 4.50%.