Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details)	Feb. 06, 2015 USD ($) shares	Jan. 21, 2015 USD ($) yr tiers indices
2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TRS Measurement, Years | yr		3
Indices Used to Compare TRS | indices		2
Number of Tiers | tiers		3
Percentage of annualized TRS 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%
Distributions Percent Before Measurement Date		10.00%
Value of MYLTIP Awards		$ 15,700,000
MYLTIP Value Amortized Into Earnings, Years | yr		4
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 (in shares) | shares	174,549
Cohen & Steers Realty Majors Portfolio Index [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TRS		50.00%
NAREIT Office Index adjusted [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TRS		50.00%
Target [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		$ 16,300,000
Threshold [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		8,200,000
High [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount of Each Tier		40,800,000
Maximum [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		40,800,000
Minimum [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		$ 0
MYLTIP Vesting 2018 [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%
Vesting Date		Feb. 04, 2018
MYLTIP vesting 2019 [Member] | 2015 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%
Vesting Date		Feb. 04, 2019