Stock Option and Incentive Plan	3 Months Ended
Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Option and Incentive Plan	10. Stock Option and Incentive Plan On January 21, 2015, the Company's Compensation Committee approved the 2015 Multi-Year, Long-Term Incentive Program awards under the Company's 2012 Plan to certain officers and employees of the Company. The 2015 MYLTIP awards utilize TRS over a three-year measurement period, on an annualized, compounded basis, as the performance metric. Earned awards will be based on the Company's TRS relative to (i) the Cohen & Steers Realty Majors Portfolio Index (50% weight) and (ii) the NAREIT Office Index adjusted to exclude the Company (50% weight). Earned awards will range from $0 to a maximum of approximately $40.8 million depending on the Company's TRS relative to the two indices, with three tiers (threshold: approximately $8.2 million; target: approximately $16.3 million; high: approximately $40.8 million) and linear interpolation between tiers. Earned awards measured on the basis of relative TRS performance are subject to an absolute TRS component in the form of relatively simple modifiers that (A) reduce the level of earned awards in the event the Company's annualized TRS is less than 0% and (B) cause some awards to be earned in the event the Company's annualized TRS is more than 12% even though on a relative basis alone the Company's TRS would not result in any earned awards. Earned awards (if any) will vest 50% on February 4, 2018 and 50% on February 4, 2019, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by the Company without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 4, 2018, earned awards will be calculated based on TRS performance up to the date of the change of control. The 2015 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units. Under the FASB's Accounting Standards Codification (“ASC”) 718 “Compensation-Stock Compensation,” the 2015 MYLTIP awards have an aggregate value of approximately $15.7 million, which amount will generally be amortized into earnings over the four-year plan period under the graded vesting method. On February 6, 2015, the measurement period for the Company’s 2012 OPP Unit awards ended and the Company’s TRS performance was sufficient for employees to earn and therefore become eligible to vest in a portion of the 2012 OPP Unit awards. The final outperformance pool was determined to be approximately $32.1 million, or approximately 80% of the total maximum outperformance pool of $40.0 million. As a result, 174,549 2012 OPP Units were automatically forfeited. During the three months ended March 31, 2015, the Company issued 30,965 shares of restricted common stock, 183,789 LTIP Units (including 85,962 LTIP Units issued on January 1, 2015 to Mortimer B. Zuckerman, non-executive Chairman of the Board, pursuant to the Transition Benefits Agreement dated March 10, 2013) and 375,000 2015 MYLTIP Units to employees and non-employee directors under the 2012 Plan. Employees and non-employee directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit and 2015 MYLTIP 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 to employees 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, 2015 were valued at approximately $4.4 million ($141.81 per share). The LTIP Units granted(excluding the number issued to Mr. Zuckerman, as discussed above) were valued at approximately $12.7 million ($129.75 per unit weighted-average fair value) using a Monte Carlo simulation method model. The per unit fair values of the LTIP Units granted were estimated on the dates of grant and for a substantial majority of such units were valued using the following assumptions: an expected life of 5.7 years, a risk-free interest rate of 1.47% and an expected price volatility of 26%. The value of the LTIP Units issued to Mr. Zuckerman was expensed between March 2013 and July 2014, in accordance with the vesting schedule set forth in the Transition Benefits Agreement. As the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units 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, 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units was approximately $10.1 million and $9.9 million for the three months ended March 31, 2015 and 2014, respectively. At March 31, 2015, there was $26.2 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $27.2 million of unrecognized compensation expense related to unvested 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units that is expected to be recognized over a weighted-average period of approximately 3.1 years.

10. Stock Option and Incentive Plan

On January 21, 2015, the Company's Compensation Committee approved the 2015 Multi-Year, Long-Term Incentive Program awards under the Company's 2012 Plan to certain officers and employees of the Company. The 2015 MYLTIP awards utilize TRS over a three-year measurement period, on an annualized, compounded basis, as the performance metric. Earned awards will be based on the Company's TRS relative to (i) the Cohen & Steers Realty Majors Portfolio Index (50% weight) and (ii) the NAREIT Office Index adjusted to exclude the Company (50% weight). Earned awards will range from $0 to a maximum of approximately $40.8 million depending on the Company's TRS relative to the two indices, with three tiers (threshold: approximately $8.2 million; target: approximately $16.3 million; high: approximately $40.8 million) and linear interpolation between tiers. Earned awards measured on the basis of relative TRS performance are subject to an absolute TRS component in the form of relatively simple modifiers that (A) reduce the level of earned awards in the event the Company's annualized TRS is less than 0% and (B) cause some awards to be earned in the event the Company's annualized TRS is more than 12% even though on a relative basis alone the Company's TRS would not result in any earned awards.

Earned awards (if any) will vest 50% on February 4, 2018 and 50% on February 4, 2019, based on continued employment. Vesting will be accelerated in the event of a change in control, termination of employment by the Company without cause, or termination of employment by the award recipient for good reason, death, disability or retirement. If there is a change of control prior to February 4, 2018, earned awards will be calculated based on TRS performance up to the date of the change of control. The 2015 MYLTIP awards are in the form of LTIP Units issued on the grant date which (i) are subject to forfeiture to the extent awards are not earned and (ii) prior to the performance measurement date are only entitled to one-tenth (10%) of the regular quarterly distributions payable on common partnership units.

Under the FASB's Accounting Standards Codification (“ASC”) 718 “Compensation-Stock Compensation,” the 2015 MYLTIP awards have an aggregate value of approximately $15.7 million, which amount will generally be amortized into earnings over the four-year plan period under the graded vesting method.

On February 6, 2015, the measurement period for the Company’s 2012 OPP Unit awards ended and the Company’s TRS performance was sufficient for employees to earn and therefore become eligible to vest in a portion of the 2012 OPP Unit awards. The final outperformance pool was determined to be approximately $32.1 million, or approximately 80% of the total maximum outperformance pool of $40.0 million. As a result, 174,549 2012 OPP Units were automatically forfeited.

During the three months ended March 31, 2015, the Company issued 30,965 shares of restricted common stock, 183,789 LTIP Units (including 85,962 LTIP Units issued on January 1, 2015 to Mortimer B. Zuckerman, non-executive Chairman of the Board, pursuant to the Transition Benefits Agreement dated March 10, 2013) and 375,000 2015 MYLTIP Units to employees and non-employee directors under the 2012 Plan. Employees and non-employee directors paid $0.01 per share of restricted common stock and $0.25 per LTIP Unit and 2015 MYLTIP 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 to employees 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, 2015 were valued at approximately $4.4 million ($141.81 per share). The LTIP Units granted(excluding the number issued to Mr. Zuckerman, as discussed above) were valued at approximately $12.7 million ($129.75 per unit weighted-average fair value) using a Monte Carlo simulation method model. The per unit fair values of the LTIP Units granted were estimated on the dates of grant and for a substantial majority of such units were valued using the following assumptions: an expected life of 5.7 years, a risk-free interest rate of 1.47% and an expected price volatility of 26%. The value of the LTIP Units issued to Mr. Zuckerman was expensed between March 2013 and July 2014, in accordance with the vesting schedule set forth in the Transition Benefits Agreement. As the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units are subject to both a service condition and a market condition, the Company recognizes the compensation expense related to the 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units 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, 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units was approximately $10.1 million and $9.9 million for the three months ended March 31, 2015 and 2014, respectively. At March 31, 2015, there was $26.2 million of unrecognized compensation expense related to unvested restricted stock and LTIP Units and $27.2 million of unrecognized compensation expense related to unvested 2012 OPP Units, 2013 MYLTIP Units, 2014 MYLTIP Units and 2015 MYLTIP Units that is expected to be recognized over a weighted-average period of approximately 3.1 years.