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Stock Option and Incentive Plan (Narrative) (Details) $ in Millions | Feb. 06, 2018 USD ($) yr | Feb. 04, 2018 USD ($) shares | Feb. 03, 2017 USD ($) shares | Feb. 04, 2016 USD ($) shares | May 15, 2012 yr shares
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MYLTIP 2013 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards | $ |  |  |  | $ 13.5 |
MYLTIP Units forfeited | shares |  |  |  | 205,762 |
Final awards percentage of target |  |  |  | 109.50% |
2012 Stock Option and Incentive Plan [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Number of Additional Shares Authorized | shares |  |  |  |  | 13,000,000
Other Than Stock Options Awards Conversion Ratio |  |  |  |  | 2.32
Stock Option Awards Conversion Ratio |  |  |  |  | 1.0
Stock Option and Incentive Plan Term Period | yr |  |  |  |  | 10
MYLTIP 2018 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
TSR measurement (in years) | yr | 3 |  |  |  |
Distributions percent before measurement date | 10.00% |  |  |  |
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% |  |  |  |
Value of MYLTIP Awards | $ | $ 13.3 |  |  |  |
MYLTIP Value Amortized Into Earnings, Years | yr | 4 |  |  |  |
MYLTIP 2014 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards | $ |  |  | $ 3.5 |  |
MYLTIP Units forfeited | shares |  |  | 447,386 |  |
Final awards percentage of target |  |  | 27.70% |  |
MYLTIP 2015 [Member] |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Value of MYLTIP Awards | $ |  | $ 3.6 |  |  |
MYLTIP Units forfeited | shares |  | 337,847 |  |  |
Final awards percentage of target |  | 22.00% |  |  |
Cohen & Steers Realty Majors Portfolio Index [Member] | MYLTIP 2018 |  |  |  |  |
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] | MYLTIP 2018 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Weighted Percentage of Index Used to Compare to TSR | 50.00% |  |  |  |
MYLTIP vesting 2021 | MYLTIP 2018 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting Percentage | 50.00% |  |  |  |
MYLTIP vesting 2022 | MYLTIP 2018 |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Vesting Percentage | 50.00% |  |  |  |

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