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Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details) | Feb. 03, 2017 USD ($) shares | Jan. 25, 2017 USD ($) yr tiers indices
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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%

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