v2.4.0.8

Investments in Unconsolidated Joint Ventures (Investments in Unconsolidated Joint Ventures) (Details) | 6 Months Ended
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Jun. 30, 2013
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 | N/A | [4]
Equity Method Investment, Ownership Percentage | 39.50% | [4]
Annapolis Junction NFM, LLC [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Properties | Annapolis Junction | [5]
Equity Method Investment, Ownership Percentage | 50.00% | [5]
Number of real estate properties | 2 |
Number of buildings under construction | 1 |
Parcels of undeveloped land | 2 |
2 GCT Venture LLC [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Properties | N/A | [6]
Equity Method Investment, Ownership Percentage | 60.00% | [6]
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 | N/A | [7]
Equity Method Investment, Ownership Percentage | 60.00% | [7]
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% |
Entity Owning Land And Infrastructure Of Project [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Equity Method Investment, Ownership Percentage | 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 also owns a 33.3% interest in the entity owning the land and infrastructure of the project.
[3] | See Note 14.
[4] | The Company acquired Mountain View Research Park and Mountain View Technology Park from the Value-Added Fund on April 10, 2013 (See Note 3). As of June 30, 2013, the investment is comprised of undistributed cash.
[5] | Comprised of two buildings, one building under construction and two undeveloped land parcels.
[6] | Two Grand Central Tower was sold on October 25, 2011. As of June 30, 2013, the investment is comprised of undistributed cash.
[7] | 125 West 55th Street was sold on May 30, 2013. As of June 30, 2013, the investment is comprised of undistributed cash.

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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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