Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details)	Feb. 03, 2017 USD ($) shares	Jan. 25, 2017 USD ($) yr indices tiers
2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Measurement, Years | yr		3
Indices Used to Compare TSR | indices		2
Number of Tiers | tiers		4
Threshold Tier		$ 10,700,000
Target Tier		21,300,000
High Tier		32,000,000
Exceptional Tier		$ 42,700,000
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%
Distributions Percent Before Measurement Date		10.00%
Value of MYLTIP Awards		$ 17,700,000
MYLTIP Value Amortized Into Earnings, Years | yr		4
MYLTIP 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards	$ 3,500,000
Final awards percentage of target	27.70%
2014 MYLTIP Units Forfeited | shares	447,386
Cohen & Steers Realty Majors Portfolio Index [Member] | 2017 MYLTIP [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] | 2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted Percentage of Index Used to Compare to TSR		50.00%
Minimum [Member] | 2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		$ 0
Maximum [Member] | 2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Potential Awards Earned		$ 42,700,000
MYLTIP vesting 2020 [Member] | 2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%
MYLTIP vesting 2021 [Member] | 2017 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage		50.00%