Mortgage Notes Payable (Notes)	9 Months Ended
Sep. 30, 2016
Mortgage Notes Payable [Abstract]
Mortgage Notes Payable Disclosure [Text Block]	5. Mortgage Notes Payable On April 11, 2016, the Company used available cash to repay the mortgage loan collateralized by its Fountain Square property located in Reston, Virginia totaling approximately $211.3 million. The mortgage loan bore interest at a fixed rate of 5.71% per annum and was scheduled to mature on October 11, 2016. There was no prepayment penalty. On September 1, 2016, the Company used a portion of the net proceeds from Boston Properties Limited Partnership’s offering of senior unsecured notes (See Note 6) and available cash to repay the mortgage loan collateralized by its 599 Lexington Avenue property located in New York City totaling $750.0 million. The mortgage loan bore interest at a fixed rate of 5.57% per annum (5.41% per annum including the impact of financing costs and interest rate hedges) and was scheduled to mature on March 1, 2017. There was no prepayment penalty. The Company recognized a gain from early extinguishment of debt totaling approximately $0.4 million consisting of the acceleration of the remaining balance related to the effective portion of a previous interest rate hedging program included within accumulated other comprehensive loss, offset by the write-off of unamortized deferred financing costs. On September 1, 2016, the Company used a portion of the net proceeds from Boston Properties Limited Partnership’s offering of senior unsecured notes (See Note 6) and available cash to repay the mortgage loan collateralized by its Embarcadero Center Four property located in San Francisco, California totaling approximately $344.8 million. The mortgage loan bore interest at a fixed rate of 6.10% per annum (7.02% per annum including the impact of financing costs and interest rate hedges)and was scheduled to mature on December 1, 2016. There was no prepayment penalty. The Company recognized a loss from early extinguishment of debt totaling approximately $0.7 million consisting of the write-off of unamortized deferred financing costs and the acceleration of the remaining balance related to the effective portion of a previous interest rate hedging program included within accumulated other comprehensive loss.

5. Mortgage Notes Payable

On April 11, 2016, the Company used available cash to repay the mortgage loan collateralized by its Fountain Square property located in Reston, Virginia totaling approximately $211.3 million. The mortgage loan bore interest at a fixed rate of 5.71% per annum and was scheduled to mature on October 11, 2016. There was no prepayment penalty.

On September 1, 2016, the Company used a portion of the net proceeds from Boston Properties Limited Partnership’s offering of senior unsecured notes (See Note 6) and available cash to repay the mortgage loan collateralized by its 599 Lexington Avenue property located in New York City totaling $750.0 million. The mortgage loan bore interest at a fixed rate of 5.57% per annum (5.41% per annum including the impact of financing costs and interest rate hedges) and was scheduled to mature on March 1, 2017. There was no prepayment penalty. The Company recognized a gain from early extinguishment of debt totaling approximately $0.4 million consisting of the acceleration of the remaining balance related to the effective portion of a previous interest rate hedging program included within accumulated other comprehensive loss, offset by the write-off of unamortized deferred financing costs.

On September 1, 2016, the Company used a portion of the net proceeds from Boston Properties Limited Partnership’s offering of senior unsecured notes (See Note 6) and available cash to repay the mortgage loan collateralized by its Embarcadero Center Four property located in San Francisco, California totaling approximately $344.8 million. The mortgage loan bore interest at a fixed rate of 6.10% per annum (7.02% per annum including the impact of financing costs and interest rate hedges)and was scheduled to mature on December 1, 2016. There was no prepayment penalty. The Company recognized a loss from early extinguishment of debt totaling approximately $0.7 million consisting of the write-off of unamortized deferred financing costs and the acceleration of the remaining balance related to the effective portion of a previous interest rate hedging program included within accumulated other comprehensive loss.