Stock Option and Incentive Plan Stock Option and Incentive Plan (Narrative) (Details) $ in Millions	Feb. 09, 2019 USD ($) shares	Feb. 05, 2019 USD ($) yr shares
2019 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Measurement, Years | yr		3
Distributions Percent Before Measurement Date		10.00%
Value of MYLTIP Awards | $		$ 13.5
MYLTIP Value Amortized Into Earnings, Years | yr		4
2016 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Value of MYLTIP Awards | $	$ 13.6
Final awards percentage of target	69.50%
2016 MYLTIP Units Forfeited	364,980
Nareit Office Index adjusted [Member] | 2019 MYLTIP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Minimum earned awards		0
Maximum Earned Awards		220,734
Target Tier		110,367