Stock Option and Incentive Plan (Narrative) (Details)				12 Months Ended
	Feb. 06, 2015 USD ($) shares	Jan. 21, 2015 USD ($) yr tiers indices	May. 15, 2012 yr shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 shares	Apr. 02, 2013 shares	Mar. 11, 2013 USD ($)
OPP Units 2012 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned	$ 40,000,000
Outperformance awards earned	$ 32,100,000
Potential maximum amount of Outperformance Awards earned (percent)	80.00%
2012 OPP Units forfeited | shares	174,549
2012 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Additional Shares Authorized | shares			13,000,000
Other Than Stock Options Awards Conversion Ratio			2.32
Stock Option Awards Conversion Ratio			1.0
Stock Option and Incentive Plan Term Period | yr			10
MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Tiers | tiers		3
TSR measurement (in years) | yr		3
Distributions percent before measurement date		10.00%
Indices Used to Compare TSR | indices		2
Percentage of annualized TSR for Reduction of Earned Awards		0.00%
Percentage to Cause Some Awards to be Earned Even if on a Relative Basis it Would Not Result in any Earned Awards		12.00%
MYLTIP units issued | shares						375,000
Value of MYLTIP Awards		$ 15,700,000
MYLTIP Value Amortized Into Earnings, Years | yr		4
Minimum [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		$ 0
Maximum [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		40,800,000
Threshold [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		8,200,000
Target [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		16,300,000
High [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		$ 40,800,000
Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
LTIP units issued (in shares) | shares							24,231
MYLTIP units issued | shares							38,926
Non-qualified stock options issued (in shares) | shares							50,847
Board of Directors Chairman [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash Payment Related to Transition Agreement								$ 6,700,000
Target Equity Award Compensation Associated with Transition Agreement								$ 11,100,000
Compensation Expense associated with Transition Agreement				$ 3,900,000	$ 13,800,000
Acceleration of Stock Based Compensation in Association with Transition Agreement					$ 12,900,000
Cohen & Steers Realty Majors Portfolio Index [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR		50.00%
NAREIT Office Index adjusted [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR		50.00%
MYLTIP Vesting 2018 [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%
MYLTIP vesting 2019 [Member] | MYLTIP 2015 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%