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Investments In Unconsolidated Joint Ventures (Investments In Unconsolidated Joint Ventures) (Details)
 3 Months Ended
Mar. 31, 2012
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
Number of buildings under construction 1
Parcels of undeveloped land 2
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% [6]
Properties Two Grand Central Tower [6]
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% [7]
Properties 500 North Capitol Street, NW [7]
Entity Owning Land And Infrastructure Of Project [Member]
  
Schedule of Equity Method Investments [Line Items]  
Nominal % Ownership 33.30%
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%
[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 is not in operation and 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.
[6] The property was sold on October 25, 2011. As of March 31, 2012, the investment is comprised of working capital and a portion of the sale proceeds.
[7] This property is under construction.