Subsequent Events	12 Months Ended
Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	19. Subsequent Events On January 10, 2019, the Company acquired land parcels at its Carnegie Center property located in Princeton, New Jersey for a purchase price of approximately $42.9 million. The Company also agreed to pay the seller additional amounts aggregating approximately $8.6 million, which are payable in the future and contingent on the development or sale of each of the parcels. The land parcels will support approximately 1.7 million square feet of development. On January 18, 2019, the Company and its partner in the consolidated entity that owns Salesforce Tower located in San Francisco, California amended the venture agreement. Per the amendment, the partner exercised its right to cause the Company to purchase on April 1, 2019 its 5% ownership interest and promoted profits interest in the venture for cash totaling approximately $210.9 million, which amount shall be reduced by approximately $24.1 million consisting of the repayment of the Company's preferred equity and preferred return as provided for in the venture agreement. As part of the original agreement, the partner was required to contribute 5% of the equity and was entitled to receive an additional promoted payment based on the success of the property (See Note 10). On January 24, 2019, the Company completed the sale of its 2600 Tower Oaks Boulevard property located in Rockville, Maryland for a gross sales price of approximately $22.7 million. 2600 Tower Oaks Boulevard is an approximately 179,000 net rentable square foot Class A office property (See Note 3). On January 24, 2019, a joint venture in which the Company has a 50% interest extended the loan collateralized by its Annapolis Junction Building Six property. At the time of the extension, the outstanding balance of the loan totaled approximately $13.0 million and was scheduled to mature on November 17, 2019, with one, one-year extension option, subject to certain conditions. The extended loan has a total commitment amount of approximately $14.3 million, bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on November 17, 2020. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet located in Annapolis, Maryland (See Note 5). On January 24, 2019, the ground lessor under the Company's 65-year ground lease for land totaling approximately 5.6 acres at Platform 16 located in San Jose, California made available for lease to the Company the remaining land parcels. As a result, the Company recognized the remaining portion of the capital lease asset and liability (See Note 3). On February 1, 2019 and February 5, 2019, Boston Properties, Inc. issued an aggregate of 23,083 shares of restricted common stock and Boston Properties Limited Partnership issued an aggregate of 172,166 LTIP units under the 2012 Plan to certain employees of Boston Properties, Inc. On February 5, 2019, Boston Properties, Inc.’s Compensation Committee approved the 2019 Multi-Year Long-Term Incentive Program (the “2019 MYLTIP”) awards under Boston Properties, Inc.’s 2012 Plan to certain officers and employees of Boston Properties, Inc. Earned awards will range from zero to a maximum of 220,734 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the FTSE Nareit Office Index, adjusted to include Vornado Realty Trust, with a target of approximately 110,367 LTIP Units and linear interpolation between zero and maximum. Under ASC 718, the 2019 MYLTIP awards have an aggregate value of approximately $13.5 million, which amount will generally be amortized into earnings over the four-year plan period under the graded vesting method. On February 9, 2019, the measurement period for the Company’s 2016 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 69.5% of target or an aggregate of approximately $13.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 364,980 2016 MYLTIP Units that had been previously granted were automatically forfeited. On February 14, 2019, the Company announced that it had entered into a 15-year lease with Google, LLC for approximately 362,000 net rentable square feet of Class A office space in a build-to-suit development project to be located at the Company’s 325 Main Street property at Kendall Center in Cambridge, Massachusetts. 325 Main Street currently consists of an approximately 115,000 net rentable square foot Class A office property that will be demolished and developed into an approximately 400,000 net rentable square foot Class A office property, including approximately 38,000 net rentable square feet of retail space. There can be no assurance that the project will commence.

19. Subsequent Events

On January 10, 2019, the Company acquired land parcels at its Carnegie Center property located in Princeton, New Jersey for a purchase price of approximately $42.9 million. The Company also agreed to pay the seller additional amounts aggregating approximately $8.6 million, which are payable in the future and contingent on the development or sale of each of the parcels. The land parcels will support approximately 1.7 million square feet of development.

On January 18, 2019, the Company and its partner in the consolidated entity that owns Salesforce Tower located in San Francisco, California amended the venture agreement. Per the amendment, the partner exercised its right to cause the Company to purchase on April 1, 2019 its 5% ownership interest and promoted profits interest in the venture for cash totaling approximately $210.9 million, which amount shall be reduced by approximately $24.1 million consisting of the repayment of the Company's preferred equity and preferred return as provided for in the venture agreement. As part of the original agreement, the partner was required to contribute 5% of the equity and was entitled to receive an additional promoted payment based on the success of the property (See Note 10).

On January 24, 2019, the Company completed the sale of its 2600 Tower Oaks Boulevard property located in Rockville, Maryland for a gross sales price of approximately $22.7 million. 2600 Tower Oaks Boulevard is an approximately 179,000 net rentable square foot Class A office property (See Note 3).

On January 24, 2019, a joint venture in which the Company has a 50% interest extended the loan collateralized by its Annapolis Junction Building Six property. At the time of the extension, the outstanding balance of the loan totaled approximately $13.0 million and was scheduled to mature on November 17, 2019, with one, one-year extension option, subject to certain conditions. The extended loan has a total commitment amount of approximately $14.3 million, bears interest at a variable rate equal to LIBOR plus 2.00% per annum and matures on November 17, 2020. Annapolis Junction Building Six is a Class A office property with approximately 119,000 net rentable square feet located in Annapolis, Maryland (See Note 5).

On January 24, 2019, the ground lessor under the Company's 65-year ground lease for land totaling approximately 5.6 acres at Platform 16 located in San Jose, California made available for lease to the Company the remaining land parcels. As a result, the Company recognized the remaining portion of the capital lease asset and liability (See Note 3).

On February 1, 2019 and February 5, 2019, Boston Properties, Inc. issued an aggregate of 23,083 shares of restricted common stock and Boston Properties Limited Partnership issued an aggregate of 172,166 LTIP units under the 2012 Plan to certain employees of Boston Properties, Inc.

On February 5, 2019, Boston Properties, Inc.’s Compensation Committee approved the 2019 Multi-Year Long-Term Incentive Program (the “2019 MYLTIP”) awards under Boston Properties, Inc.’s 2012 Plan to certain officers and employees of Boston Properties, Inc. Earned awards will range from zero to a maximum of 220,734 LTIP Units depending on Boston Properties, Inc.’s TSR relative to the FTSE Nareit Office Index, adjusted to include Vornado Realty Trust, with a target of approximately 110,367 LTIP Units and linear interpolation between zero and maximum. Under ASC 718, the 2019 MYLTIP awards have an aggregate value of approximately $13.5 million, which amount will generally be amortized into earnings over the four-year plan period under the graded vesting method.

On February 9, 2019, the measurement period for the Company’s 2016 MYLTIP awards ended and, based on Boston Properties, Inc.’s relative TSR performance, the final awards were determined to be 69.5% of target or an aggregate of approximately $13.6 million (after giving effect to voluntary employee separations). As a result, an aggregate of 364,980 2016 MYLTIP Units that had been previously granted were automatically forfeited.

On February 14, 2019, the Company announced that it had entered into a 15-year lease with Google, LLC for approximately 362,000 net rentable square feet of Class A office space in a build-to-suit development project to be located at the Company’s 325 Main Street property at Kendall Center in Cambridge, Massachusetts. 325 Main Street currently consists of an approximately 115,000 net rentable square foot Class A office property that will be demolished and developed into an approximately 400,000 net rentable square foot Class A office property, including approximately 38,000 net rentable square feet of retail space. There can be no assurance that the project will commence.