Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details)	12 Months Ended
	Dec. 31, 2012
Square 407 Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Market Square North
Equity Method Investment, Ownership Percentage	50.00%
The Metropolitan Square Associates LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Metropolitan Square
Equity Method Investment, Ownership Percentage	51.00%
BP/CRF 901 New York Avenue LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	901 New York Avenue	[1]
Equity Method Investment, Ownership Percentage	25.00%	[1]
WP Project Developer LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Wisconsin Place Land and Infrastructure	[2]
Equity Method Investment, Ownership Percentage	33.30%	[2]
RBP Joint Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Eighth Avenue and 46th Street	[3]
Equity Method Investment, Ownership Percentage	50.00%	[3]
Boston Properties Office Value-Added Fund, L.P. [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Mountain View Research and Technology Parks	[1]
Equity Method Investment, Ownership Percentage	39.50%	[1]
Annapolis Junction NFM, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Annapolis Junction	[4]
Equity Method Investment, Ownership Percentage	50.00%	[4]
Number of real estate properties	1
Number of buildings under construction	2
Parcels of undeveloped land	2
767 Venture, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	767 Fifth Avenue (The GM Building)
Equity Method Investment, Ownership Percentage	60.00%
2 GCT Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Two Grand Central Tower	[5]
Equity Method Investment, Ownership Percentage	60.00%	[5]
540 Madison Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	540 Madison Avenue
Equity Method Investment, Ownership Percentage	60.00%
125 West 55th Street Venture LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	125 West 55th Street
Equity Method Investment, Ownership Percentage	60.00%
500 North Capitol LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	500 North Capitol Street, NW
Equity Method Investment, Ownership Percentage	30.00%	[6]
Entity Owning Land And Infrastructure Of Project [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	33.30%
Transit Tower Site LLC [Member]
Schedule of Equity Method Investments [Line Items]
Properties	Transbay Tower
Equity Method Investment, Ownership Percentage	50.00%	[7]

[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 also owns a 33.3% interest in the entity owning the land, parking and infrastructure of the project.

[3] This property is not in operation and consists of assembled land.

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

[5] The property was sold on October 25, 2011. As of December 31, 2012, the investment is comprised of working capital and a portion of undistributed sale proceeds.

[6] This property has been partially placed in-service.

[7] See Note 20.