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Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details) | Feb. 04, 2016 USD ($) shares | Jan. 25, 2016 USD ($) yr indices tiers | Feb. 06, 2015 USD ($) shares
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2016 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 |  | 3 |
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 |  | $ 17,300,000 |
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
2012 OPP Units Forfeited | shares |  |  | 174,549
Outperformance awards earned |  |  | $ 32,100,000
Potential maximum amount of Outperformance Awards earned (percent) |  |  | 80.00%
2013 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Value of MYLTIP Awards | $ 13,500,000 |  |
Final awards percentage of target | 109.50% |  |
2013 MYLTIP Units Forfeited | shares | 205,762 |  |
Cohen & Steers Realty Majors Portfolio Index [Member] | 2016 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] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Weighted Percentage of Index Used to Compare to TSR |  | 50.00% |
Threshold [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Amount of Each Tier |  | $ 9,900,000 |
Target [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Amount of Each Tier |  | 19,700,000 |
High [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Amount of Each Tier |  | 49,300,000 |
Maximum [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Potential Awards Earned |  | 49,300,000 |
Minimum [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Potential Awards Earned |  | $ 0 |
MYLTIP vesting 2019 [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting Percentage |  | 50.00% |
MYLTIP vesting 2020 [Member] | 2016 MYLTIP [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting Percentage |  | 50.00% |

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