Stock Option And Incentive Plan	3 Months Ended
Mar. 31, 2012
Stock Option And Incentive Plan [Abstract]
Stock Option And Incentive Plan	11. Stock Option and Incentive Plan On January 25, 2012, the Compensation Committee of the Board of Directors of the Company approved outperformance awards under the Company's 1997 Stock Option and Incentive Plan (the "1997 Plan") to certain officers of the Company. These awards (the "2012 OPP Awards") are part of a broad-based, long-term incentive compensation program designed to provide the Company's management team with the potential to earn equity awards subject to the Company "outperforming" and creating shareholder value in a pay-for-performance structure. 2012 OPP Awards utilize total return to shareholders ("TRS") over a three-year measurement period as the performance metric and include two years of time-based vesting after the end of the performance measurement period (subject to acceleration in certain events) as a retention tool. Recipients of 2012 OPP Awards will share in an outperformance pool if the Company's TRS, including both share appreciation and dividends, exceeds absolute and relative hurdles over a three-year measurement period from February 7, 2012 to February 6, 2015, based on the average closing price of a share of the Company's common stock of $106.69 for the five trading days prior to and including February 7, 2012. The aggregate reward that recipients of all 2012 OPP Awards can earn, as measured by the outperformance pool, is subject to a maximum cap of $40.0 million. The outperformance pool will consist of (i) two percent (2%) of the excess total return above a cumulative absolute TRS hurdle of 24% over the full three-year measurement period (equivalent to 8% per annum) (the "Absolute TRS Component") and (ii) two percent (2%) of the excess or deficient excess total return above or below a relative TRS hurdle equal to the total return of the SNL Equity REIT Index over the three-year measurement period (the "Relative TRS Component"). In the event that the Relative TRS Component is potentially positive because the Company's TRS is greater than the total return of the SNL Equity REIT Index, but the Company achieves a cumulative absolute TRS below 24% over the three-year measurement period (equivalent to 8% per annum), the actual contribution to the outperformance pool from the Relative TRS Component will be subject to a sliding scale factor as follows: (i) 100% of the potential Relative TRS Component will be earned if the Company's TRS is equal to or greater than a cumulative 24% over three years, (ii) 0% will be earned if the Company's TRS is 0% or less, and (iii) a percentage from 0% to 100% calculated by linear interpolation will be earned if the Company's cumulative TRS over three years is between 0% and 24%. For example, if the Company achieves a cumulative absolute TRS of 18% over the full three-year measurement period (equivalent to a 6% absolute annual TRS), the potential Relative TRS Component would be prorated by 75%. The potential Relative TRS Component before application of the sliding scale factor will be capped at $40.0 million. In the event that the Relative TRS Component is negative because the Company's TRS is less than the total return of the SNL Equity REIT Index, any outperformance reward potentially earned under the Absolute TRS Component will be reduced dollar for dollar, provided that the potential Absolute TRS Component before reduction for any negative Relative TRS Component will be capped at $40.0 million. The algebraic sum of the Absolute TRS Component and the Relative TRS Component determined as described above will never exceed $40.0 million. Each employee's 2012 OPP Award was designated as a specified percentage of the aggregate outperformance pool. Assuming the applicable absolute and/or relative TRS thresholds are achieved at the end of the measurement period, the algebraic sum of the Absolute TRS Component and the Relative TRS Component will be calculated and then allocated among the 2012 OPP Award recipients in accordance with each individual's percentage. If there is a change of control prior to February 6, 2015, the measurement period will end on the change of control date and both the Absolute TRS Component (using a prorated absolute TRS hurdle) and the Relative TRS Component will be calculated and, assuming the applicable absolute and/or relative TRS thresholds are achieved over the shorter measurement period, allocated among the 2012 OPP Award recipients as of that date. Rewards earned with respect to 2012 OPP Awards (if any) will vest 25% on February 7, 2015, 25% on February 7, 2016 and 50% on February 7, 2017, based on continued employment. Vesting will be accelerated in the event of a change in control of the Company, termination of employment without cause, termination of employment by the award recipient for good reason, death, disability or retirement, although restrictions on transfer will continue to apply in certain of these situations. All determinations, interpretations and assumptions relating to the calculation of performance and vesting relating to 2012 OPP Awards will be made by the Compensation Committee. 2012 OPP Awards will be in the form of LTIP Units. LTIP Units will be issued prior to the determination of the outperformance pool, but will remain subject to forfeiture depending on the extent of rewards earned with respect to 2012 OPP Awards. The number of LTIP Units issued initially to recipients of the 2012 OPP Awards is an estimate of the maximum number of LTIP Units that they could earn, based on certain assumptions. The number of LTIP Units actually earned by each award recipient will be determined at the end of the performance measurement period by dividing his or her share of the outperformance pool by the average closing price of a REIT Share for the 15 trading days immediately preceding the measurement date. Total return for the Company and for the SNL Equity REIT Index over the three-year measurement period and other circumstances will determine how many LTIP Units are earned by each recipient; if they are fewer than the number issued initially, the balance will be forfeited as of the performance measurement date. Prior to the measurement date, LTIP units issued on account of 2012 OPP Awards will be entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of LTIP Units, both vested and unvested, which 2012 OPP Award recipients have earned based on the establishment of an outperformance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit. LTIP Units are designed to qualify as "profits interests" in the Operating Partnership for federal income tax purposes. As a general matter, the profits interests characteristics of the LTIP Units mean that initially they will not be economically equivalent in value to an OP Unit. If and when events specified by applicable tax regulations occur, LTIP Units can over time increase in value up to the point where they are equivalent to OP Units on a one-for-one basis. After LTIP Units are fully vested, and to the extent the special tax rules applicable to profits interests have allowed them to become equivalent in value to OP Units, LTIP Units may be converted on a one-for-one basis into OP Units. OP Units in turn have a one-for-one relationship in value with Boston Properties, Inc. common stock, and are exchangeable on such one-for-one basis for cash or, at the election of the Company, Boston Properties, Inc. common stock. The 2012 OPP Units were valued, in accordance with ASC 718 "Compensation—Stock Compensation," at an aggregate of approximately $7.7 million utilizing a Monte Carlo simulation to estimate the probability of the performance vesting conditions being satisfied. The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times. For each simulation, the payoff is calculated at the settlement date, which is then discounted to the award date at a risk-free interest rate. The average of the values over all simulations is the expected value of the unit on the award date. Assumptions used in the valuations included (1) factors associated with the underlying performance of the Company's stock price and total shareholder return over the term of the performance awards including total stock return volatility and risk-free interest and (2) factors associated with the relative performance of the Company's stock price and total shareholder return when compared to the SNL Equity REIT Index. The valuation was performed in a risk-neutral framework, so no assumption was made with respect to an equity risk premium. The fair value of the 2012 OPP Units is based on the sum of: (1) the present value of the expected payoff to the OPP Award on the measurement date, if the TRS over the applicable measurement period exceeds performance hurdles of the Absolute and the Relative Components; and (2) the present value of the distributions payable on the 2012 OPP Units. The ultimate reward realized on account of the OPP Award by the holders of the 2012 OPP Units is contingent on the TRS achieved on the measurement date, both in absolute terms and relative to the TRS of the SNL Equity REIT Index. The per unit fair value of each 2012 OPP Unit was estimated on the date of grant using the following assumptions in the Monte Carlo valuation: expected price volatility for the Company and the SNL Equity REIT index of 31% and 30%, respectively; a risk free rate of 0.35%; and total dividend payments over the measurement period of $7.28 per share. On February 13, 2012, E. Mitchell Norville announced that he would resign as Executive Vice President, Chief Operating Officer of the Company effective on February 29, 2012. In connection with his resignation, Mr. Norville entered into a separation agreement (the "Separation Agreement") with the Company. Under the Separation Agreement, the Company agreed to pay Mr. Norville cash payments totaling approximately $1,533,333 (less applicable deductions) in addition to his cash bonus for 2011, which was $950,000. In addition, Mr. Norville agreed to provide consulting services to the Company for at least two months following the effective date of his resignation for which he will receive $20,000 per month. Under the Separation Agreement, Mr. Norville is entitled to accelerated vesting with respect to 23,502 LTIP units in the Operating Partnership and stock options to purchase 4,464 shares of common stock at an exercise price of $92.71 and 5,117 shares of common stock at an exercise price of $104.47. Mr. Norville will also retain approximately 36% of his 2011 outperformance award, which will remain subject to the performance-based vesting criteria originally established for the 2011 outperformance awards. Mr. Norville agreed to one-year non-competition, non-solicitation and non-interference provisions, and provided the Company with a general release of claims. The Company recognized approximately $4.5 million of expense during the three months ended March 31, 2012 in connection with Mr. Norville's resignation. During the three months ended March 31, 2012, the Company issued 19,521 shares of restricted common stock, 186,007 non-qualified stock options, 169,301 LTIP Units and 400,000 2012 OPP Units to employees and non-employee directors under the 1997 Plan. Employees and directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit and OPP Unit. An LTIP Unit is generally the economic equivalent of a share of restricted stock in the Company. The aggregate value of the LTIP Units is included in noncontrolling interests in the Consolidated Balance Sheets. Grants of restricted stock and LTIP Units vest in four equal annual installments. Restricted stock is measured at fair value on the date of grant based on the number of shares granted, as adjusted for forfeitures, and the closing price of the Company's Common Stock on the date of grant as quoted on the New York Stock Exchange. Such value is recognized as an expense ratably over the corresponding employee service period. The shares of restricted stock granted during the three months ended March 31, 2012 were valued at approximately $2.1 million ($107.57 per share). The non-qualified stock options granted during the three months ended March 31, 2012 had a weighted-average fair value on the date of grant of $19.50 per option, which was computed using the Black-Scholes option-pricing model utilizing the following weighted-average assumptions: an expected life of 5.4 years, a risk-free interest rate of 0.92%, an expected price volatility of 28.4% and an expected dividend yield of 2.9%. The weighted-average exercise price of the options is $107.23, which was the weighted-average closing price of the Company's common stock on the date of grant. The LTIP Units granted during the three months ended March 31, 2012 were valued at approximately $16.8 million ($98.94 per unit fair value weighted-average) using a Monte Carlo simulation method model. The weighted-average per unit fair value of each LTIP Unit granted was estimated on the date of grant using the following assumptions: an expected life of 5.8 years, a risk-free interest rate of 0.94% and an expected price volatility of 29.1%. As the 2011 OPP Awards and 2012 OPP Awards are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2011 OPP Awards and 2012 OPP Awards under the graded vesting attribution method. Under the graded vesting attribution method, each portion of the award that vests at a different date is accounted for as a separate award and recognized over the period appropriate to that portion so that the compensation cost for each portion should be recognized in full by the time that portion vests. Dividends paid on both vested and unvested shares of restricted stock are charged directly to Dividends in Excess of Earnings in the Consolidated Balance Sheets. Aggregate stock-based compensation expense associated with restricted stock, non-qualified stock options, LTIP Units, 2008 OPP Units, 2011 OPP Units and 2012 OPP Units was approximately $10.9 million and $11.6 million for the three months ended March 31, 2012 and 2011, respectively. For the three months ended March 31, 2012, stock-based compensation expense includes approximately $2.7 million consisting of the acceleration of vesting of the Company's Chief Operating Officer's stock-based compensation awards associated with his resignation. Upon the conclusion of the three-year measurement period in February 2011, the 2008 OPP Awards were not earned, the program was terminated and the Company accelerated the then remaining unrecognized compensation expense totaling approximately $4.3 million during the three months ended March 31, 2011. At March 31, 2012, there was $34.4 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $11.4 million of unrecognized compensation expense related to unvested 2011 OPP Units and 2012 OPP Units that is expected to be recognized over a weighted-average period of approximately 3.0 years.

11. Stock Option and Incentive Plan

On January 25, 2012, the Compensation Committee of the Board of Directors of the Company approved outperformance awards under the Company's 1997 Stock Option and Incentive Plan (the "1997 Plan") to certain officers of the Company. These awards (the "2012 OPP Awards") are part of a broad-based, long-term incentive compensation program designed to provide the Company's management team with the potential to earn equity awards subject to the Company "outperforming" and creating shareholder value in a pay-for-performance structure. 2012 OPP Awards utilize total return to shareholders ("TRS") over a three-year measurement period as the performance metric and include two years of time-based vesting after the end of the performance measurement period (subject to acceleration in certain events) as a retention tool. Recipients of 2012 OPP Awards will share in an outperformance pool if the Company's TRS, including both share appreciation and dividends, exceeds absolute and relative hurdles over a three-year measurement period from February 7, 2012 to February 6, 2015, based on the average closing price of a share of the Company's common stock of $106.69 for the five trading days prior to and including February 7, 2012. The aggregate reward that recipients of all 2012 OPP Awards can earn, as measured by the outperformance pool, is subject to a maximum cap of $40.0 million.

The outperformance pool will consist of (i) two percent (2%) of the excess total return above a cumulative absolute TRS hurdle of 24% over the full three-year measurement period (equivalent to 8% per annum) (the "Absolute TRS Component") and (ii) two percent (2%) of the excess or deficient excess total return above or below a relative TRS hurdle equal to the total return of the SNL Equity REIT Index over the three-year measurement period (the "Relative TRS Component"). In the event that the Relative TRS Component is potentially positive because the Company's TRS is greater than the total return of the SNL Equity REIT Index, but the Company achieves a cumulative absolute TRS below 24% over the three-year measurement period (equivalent to 8% per annum), the actual contribution to the outperformance pool from the Relative TRS Component will be subject to a sliding scale factor as follows: (i) 100% of the potential Relative TRS Component will be earned if the Company's TRS is equal to or greater than a cumulative 24% over three years, (ii) 0% will be earned if the Company's TRS is 0% or less, and (iii) a percentage from 0% to 100% calculated by linear interpolation will be earned if the Company's cumulative TRS over three years is between 0% and 24%. For example, if the Company achieves a cumulative absolute TRS of 18% over the full three-year measurement period (equivalent to a 6% absolute annual TRS), the potential Relative TRS Component would be prorated by 75%. The potential Relative TRS Component before application of the sliding scale factor will be capped at $40.0 million. In the event that the Relative TRS Component is negative because the Company's TRS is less than the total return of the SNL Equity REIT Index, any outperformance reward potentially earned under the Absolute TRS Component will be reduced dollar for dollar, provided that the potential Absolute TRS Component before reduction for any negative Relative TRS Component will be capped at $40.0 million. The algebraic sum of the Absolute TRS Component and the Relative TRS Component determined as described above will never exceed $40.0 million.

Each employee's 2012 OPP Award was designated as a specified percentage of the aggregate outperformance pool. Assuming the applicable absolute and/or relative TRS thresholds are achieved at the end of the measurement period, the algebraic sum of the Absolute TRS Component and the Relative TRS Component will be calculated and then allocated among the 2012 OPP Award recipients in accordance with each individual's percentage. If there is a change of control prior to February 6, 2015, the measurement period will end on the change of control date and both the Absolute TRS Component (using a prorated absolute TRS hurdle) and the Relative TRS Component will be calculated and, assuming the applicable absolute and/or relative TRS thresholds are achieved over the shorter measurement period, allocated among the 2012 OPP Award recipients as of that date.

Rewards earned with respect to 2012 OPP Awards (if any) will vest 25% on February 7, 2015, 25% on February 7, 2016 and 50% on February 7, 2017, based on continued employment. Vesting will be accelerated in the event of a change in control of the Company, termination of employment without cause, termination of employment by the award recipient for good reason, death, disability or retirement, although restrictions on transfer will continue to apply in certain of these situations. All determinations, interpretations and assumptions relating to the calculation of performance and vesting relating to 2012 OPP Awards will be made by the Compensation Committee. 2012 OPP Awards will be in the form of LTIP Units. LTIP Units will be issued prior to the determination of the outperformance pool, but will remain subject to forfeiture depending on the extent of rewards earned with respect to 2012 OPP Awards. The number of LTIP Units issued initially to recipients of the 2012 OPP Awards is an estimate of the maximum number of LTIP Units that they could earn, based on certain assumptions. The number of LTIP Units actually earned by each award recipient will be determined at the end of the performance measurement period by dividing his or her share of the outperformance pool by the average closing price of a REIT Share for the 15 trading days immediately preceding the measurement date. Total return for the Company and for the SNL Equity REIT Index over the three-year measurement period and other circumstances will determine how many LTIP Units are earned by each recipient; if they are fewer than the number issued initially, the balance will be forfeited as of the performance measurement date. Prior to the measurement date, LTIP units issued on account of 2012 OPP Awards will be entitled to receive per unit distributions equal to one-tenth (10%) of the regular quarterly distributions payable on an OP Unit, but will not be entitled to receive any special distributions. After the measurement date, the number of LTIP Units, both vested and unvested, which 2012 OPP Award recipients have earned based on the establishment of an outperformance pool, will be entitled to receive distributions in an amount per unit equal to distributions, both regular and special, payable on an OP Unit. LTIP Units are designed to qualify as "profits interests" in the Operating Partnership for federal income tax purposes. As a general matter, the profits interests characteristics of the LTIP Units mean that initially they will not be economically equivalent in value to an OP Unit. If and when events specified by applicable tax regulations occur, LTIP Units can over time increase in value up to the point where they are equivalent to OP Units on a one-for-one basis. After LTIP Units are fully vested, and to the extent the special tax rules applicable to profits interests have allowed them to become equivalent in value to OP Units, LTIP Units may be converted on a one-for-one basis into OP Units. OP Units in turn have a one-for-one relationship in value with Boston Properties, Inc. common stock, and are exchangeable on such one-for-one basis for cash or, at the election of the Company, Boston Properties, Inc. common stock.

The 2012 OPP Units were valued, in accordance with ASC 718 "Compensation—Stock Compensation," at an aggregate of approximately $7.7 million utilizing a Monte Carlo simulation to estimate the probability of the performance vesting conditions being satisfied. The Monte Carlo simulation used a statistical formula underlying the Black-Scholes and binomial formulas and such simulation was run approximately 100,000 times. For each simulation, the payoff is calculated at the settlement date, which is then discounted to the award date at a risk-free interest rate. The average of the values over all simulations is the expected value of the unit on the award date. Assumptions used in the valuations included (1) factors associated with the underlying performance of the Company's stock price and total shareholder return over the term of the performance awards including total stock return volatility and risk-free interest and (2) factors associated with the relative performance of the Company's stock price and total shareholder return when compared to the SNL Equity REIT Index. The valuation was performed in a risk-neutral framework, so no assumption was made with respect to an equity risk premium. The fair value of the 2012 OPP Units is based on the sum of: (1) the present value of the expected payoff to the OPP Award on the measurement date, if the TRS over the applicable measurement period exceeds performance hurdles of the Absolute and the Relative Components; and (2) the present value of the distributions payable on the 2012 OPP Units. The ultimate reward realized on account of the OPP Award by the holders of the 2012 OPP Units is contingent on the TRS achieved on the measurement date, both in absolute terms and relative to the TRS of the SNL Equity REIT Index. The per unit fair value of each 2012 OPP Unit was estimated on the date of grant using the following assumptions in the Monte Carlo valuation: expected price volatility for the Company and the SNL Equity REIT index of 31% and 30%, respectively; a risk free rate of 0.35%; and total dividend payments over the measurement period of $7.28 per share.

On February 13, 2012, E. Mitchell Norville announced that he would resign as Executive Vice President, Chief Operating Officer of the Company effective on February 29, 2012. In connection with his resignation, Mr. Norville entered into a separation agreement (the "Separation Agreement") with the Company. Under the Separation Agreement, the Company agreed to pay Mr. Norville cash payments totaling approximately $1,533,333 (less applicable deductions) in addition to his cash bonus for 2011, which was $950,000. In addition, Mr. Norville agreed to provide consulting services to the Company for at least two months following the effective date of his resignation for which he will receive $20,000 per month. Under the Separation Agreement, Mr. Norville is entitled to accelerated vesting with respect to 23,502 LTIP units in the Operating Partnership and stock options to purchase 4,464 shares of common stock at an exercise price of $92.71 and 5,117 shares of common stock at an exercise price of $104.47. Mr. Norville will also retain approximately 36% of his 2011 outperformance award, which will remain subject to the performance-based vesting criteria originally established for the 2011 outperformance awards. Mr. Norville agreed to one-year non-competition, non-solicitation and non-interference provisions, and provided the Company with a general release of claims. The Company recognized approximately $4.5 million of expense during the three months ended March 31, 2012 in connection with Mr. Norville's resignation.

During the three months ended March 31, 2012, the Company issued 19,521 shares of restricted common stock, 186,007 non-qualified stock options, 169,301 LTIP Units and 400,000 2012 OPP Units to employees and non-employee directors under the 1997 Plan. Employees and directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit and OPP Unit. An LTIP Unit is generally the economic equivalent of a share of restricted stock in the Company. The aggregate value of the LTIP Units is included in noncontrolling interests in the Consolidated Balance Sheets. Grants of restricted stock and LTIP Units vest in four equal annual installments. Restricted stock is measured at fair value on the date of grant based on the number of shares granted, as adjusted for forfeitures, and the closing price of the Company's Common Stock on the date of grant as quoted on the New York Stock Exchange. Such value is recognized as an expense ratably over the corresponding employee service period. The shares of restricted stock granted during the three months ended March 31, 2012 were valued at approximately $2.1 million ($107.57 per share). The non-qualified stock options granted during the three months ended March 31, 2012 had a weighted-average fair value on the date of grant of $19.50 per option, which was computed using the Black-Scholes option-pricing model utilizing the following weighted-average assumptions: an expected life of 5.4 years, a risk-free interest rate of 0.92%, an expected price volatility of 28.4% and an expected dividend yield of 2.9%. The weighted-average exercise price of the options is $107.23, which was the weighted-average closing price of the Company's common stock on the date of grant. The LTIP Units granted during the three months ended March 31, 2012 were valued at approximately $16.8 million ($98.94 per unit fair value weighted-average) using a Monte Carlo simulation method model. The weighted-average per unit fair value of each LTIP Unit granted was estimated on the date of grant using the following assumptions: an expected life of 5.8 years, a risk-free interest rate of 0.94% and an expected price volatility of 29.1%. As the 2011 OPP Awards and 2012 OPP Awards are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2011 OPP Awards and 2012 OPP Awards under the graded vesting attribution method. Under the graded vesting attribution method, each portion of the award that vests at a different date is accounted for as a separate award and recognized over the period appropriate to that portion so that the compensation cost for each portion should be recognized in full by the time that portion vests. Dividends paid on both vested and unvested shares of restricted stock are charged directly to Dividends in Excess of Earnings in the Consolidated Balance Sheets. Aggregate stock-based compensation expense associated with restricted stock, non-qualified stock options, LTIP Units, 2008 OPP Units, 2011 OPP Units and 2012 OPP Units was approximately $10.9 million and $11.6 million for the three months ended March 31, 2012 and 2011, respectively. For the three months ended March 31, 2012, stock-based compensation expense includes approximately $2.7 million consisting of the acceleration of vesting of the Company's Chief Operating Officer's stock-based compensation awards associated with his resignation. Upon the conclusion of the three-year measurement period in February 2011, the 2008 OPP Awards were not earned, the program was terminated and the Company accelerated the then remaining unrecognized compensation expense totaling approximately $4.3 million during the three months ended March 31, 2011. At March 31, 2012, there was $34.4 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $11.4 million of unrecognized compensation expense related to unvested 2011 OPP Units and 2012 OPP Units that is expected to be recognized over a weighted-average period of approximately 3.0 years.