Stock Option and Incentive Plan Stock option and incentive plan (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended			0 Months Ended													9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Mar. 11, 2013	Jan. 28, 2013 MYLTIP [Member] indices Y	Jan. 28, 2013 MYLTIP [Member] Cohen & Steers Realty Majors Portfolio Index [Member]	Jan. 28, 2013 MYLTIP [Member] NAREIT Office Index adjusted [Member]	Jan. 28, 2013 MYLTIP [Member] Minimum [Member]	Jan. 28, 2013 MYLTIP [Member] Maximum [Member]	Jan. 28, 2013 MYLTIP [Member] Threshold [Member]	Jan. 28, 2013 MYLTIP [Member] Target [Member]	Jan. 28, 2013 MYLTIP [Member] Exceptional [Member]	Jan. 28, 2013 MYLTIP [Member] High [Member]	Jan. 28, 2013 MYLTIP Vesting 2016 [Member] MYLTIP [Member]	Jan. 28, 2013 MYLTIP Vesting 2017 [Member] MYLTIP [Member]	Jan. 28, 2013 MYLTIP Vesting 2018 [Member] MYLTIP [Member]	Apr. 02, 2013 Chief Executive Officer [Member]	Sep. 30, 2013 Board of Directors Chairman [Member]	Jul. 01, 2014 Board of Directors Chairman [Member]	Oct. 01, 2013 Board of Directors Chairman [Member]	Mar. 11, 2013 Board of Directors Chairman [Member]	Mar. 10, 2013 Board of Directors Chairman [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 6,200,000	$ 6,400,000	$ 38,100,000	$ 23,800,000
Non-qualified stock options issued																		50,847
TRS Measurement, Years						3
Weighted Percentage of Index Used to Compare to TRS							50.00%	50.00%
Potential Awards Earned									0	30,700,000
Indices Used to Compare TRS						2
Number of Tiers						4
Amount of Each Tier											5,100,000	10,200,000	30,700,000	20,500,000
Percentage of annualized TRS for Reduction of Earned Awards						2.00%
Percentage to Cause Some Awards to be Earned Even if on a Relative Basis it Would Not Result in any Earned Awards						10.00%
Vesting Percentage															25.00%	25.00%	50.00%			33.33333%	33.33333%		33.33333%
Vesting Date															Feb. 04, 2016	Feb. 04, 2017	Feb. 04, 2018
Distributions Percent Before Measurement Date						10.00%
Value of MYLTIP Awards						9,200,000
MYLTIP Value Amortized Into Earnings, Years						5
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																			11,800,000
Acceleration of Stock Based Compensation in Association with Transition Agreement																			$ 12,900,000
LTIP units issued (in shares)																		24,231