Investments In Unconsolidated Joint Ventures (Investments In Unconsolidated Joint Ventures) (Details)	9 Months Ended
	Sep. 30, 2011
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	50.00%
Properties	Market Square North
The Metropolitan Square Associates LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	51.00%
Properties	Metropolitan Square
BP/CRF 901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	25.00%	[1]
Properties	901 New York Avenue	[1]
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	33.30%	[2]
Properties	Wisconsin Place Land and Infrastructure	[2]
RBP Joint Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	50.00%	[3]
Properties	Eighth Avenue and 46th Street	[3]
Boston Properties Office Value-Added Fund, L.P. [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	37.60%	[1],[4]
Properties	300 Billerica Road and Mountain View Research and Technology Parks	[1],[4]
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	50.00%	[5]
Properties	Annapolis Junction	[5]
Number of real estate properties	1
Parcels of undeveloped land	2
Annapolis Junction NFM, LLC [Member] | Under Construction [Member]
Schedule of Equity Method Investments [Line Items]
Number of real estate properties	1
767 Venture, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	60.00%
Properties	The General Motors Building
2 GCT Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	60.00%
Properties	Two Grand Central Tower
540 Madison Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	60.00%
Properties	540 Madison Avenue
125 West 55th Street Venture, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	60.00%
Properties	125 West 55th Street
500 North Capitol LLC [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	30.00%
Properties	500 North Capitol Street, NW
300 Billerica Road [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	25.00%
Mountain View Research And Technology Park [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	39.50%
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Nominal % Ownership	33.30%

[1] The Company's economic ownership can increase based on the achievement of certain return thresholds.

[2] The Company's wholly-owned entity that owns the office component of the project owns a 33.3% interest in the entity owning the land and infrastructure of the project.

[3] This property consists of assembled land.

[4] Represents the Company's effective ownership interest. The Company has a 25.0% interest in the 300 Billerica Road property and a 39.5% interest in the Mountain View Research and Technology Park properties.

[5] Comprised of one building, one building under construction and two undeveloped land parcels.